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2. 0 0 0 .6 , "0f" 3. - 4. William J. Bacha, Jr., PhDProfessor Emeritus Department of Biology Rutgers University Camden College of Arts and Sciences Camden, New Jersey Linda M. Bacha, MS, VMD Assistant Professor of BiologyDepartment of Biology Camden County College Blackwood, New Jersey/LIpPINCOTT WILLIAMS & WILKINSA Wolters Kluwer CompanyPhiladelphia Baltimore New York LondonBuenos Aires Hong Kong Sydney Tokyo , 5. Editor: Donna BaladoManaging Editor: Dana BattagliaMarketing Manager: Anne SmithProduction Editor: Jennifer D. WeirCopyright 2000 Lippincott Williams & Wilkins351 West Camden StreetBaltimore, Maryland 21201-2436530 Walnut StreetPhiladelphia, Pennsylvania 19106-3621All rights reserved. This book is protected by copyright. No part of thisbook may be reproduced in any form or by any means, including pho-tocopying, or utilized by any information storage and retrieval systemwithout written permission from the copyright owner.The publisher is not responsible (as a matter of product liability, negli-gence, or otherwise) for any injury resulting from any material con-tained herein. This publication contains information relating to generalprinciples of medical care which should not be construed as specific in-structions for individual patients. Manufacturers product informationand package inserts should be reviewed for current information, in-cluding contraindications, dosages and precautions.Printed in the United States of AmericaFirst Edition, 1990Library of Congress Cataloging-in-Publication DataBacha, William J.Color atlas of veterinary histology / William J. Bacha, Jr., Linda M.Bacha. 2nd ed. p. cm.Includes bibliographical references (p.).ISBN 0-683-30618-91. Veterinary histology Atlases. 1. Bacha, Linda M. II. Title.SF757.3.B332000636.0891018 dc2199-046388The publishers have made every effort to trace the copyright holders forborrowed material. If they have inadvertently overlooked any, they willbe pleased to make the necessary arrangements at the first opportunity.To purchase additional copies of this book, call our customer service de-partment at (800) 638-3030 or fax orders to (301) 824-7390. Interna-tional customers should call (301) 714-2324. 05 065 6 7 8 9 10 6. THIS BOOIS DEDICATED TO~v 7. e wish to thank those who have dred others. Four of the original black andused the first edition for their white line drawings have also been re-suggestions. We believe the in-drawn. Also, a glossary of nearly 750corporation of many of these recommen- words has been added.dations will make this edition even moreThe style, format, and . purpose of thishelpful to the user. edition remain essentially unchanged from To this end, we have updated the mate-the first edition. We continue to view therial for the second edition by scanning all of atlas as a useful, benchside reference forthe original kodachromes and relabelingthose interested in understanding and in-the art. We have added thirteen new pho- terpreting histologic and cytologic prepa-tographs and have enlarged over one hun- ratIOns. VII 8. lthough we have written this atlas All photomicrographs and drawingsprimarily to fulfill a need of the stu- are original. Some drawings were donedent of veterinary medicine, we be- freehand, while others were made with thelieve that clinicians, private practitioners, aid of a camera lucida. Light microscopyand researchers will find it a useful refer-and colored photomicrographs have beenence for normal tissues and organs. Cur-used exclusively. We have chosen colorrently, students rely heavily, if not exclu-rather than black and white because of itssively, on atlases of human histology for correspondence to stained preparations.guidance in the laboratory. There are, of With the exception of the few histologiccourse, similarities between organs and preparations loaned to us by generoustissues of domestic animals and those ofdonors or purchased from a dealer, slideshumans. There are also differences, how-were prepared by the authors. Fresh organever, and these are rarely encountered in samples were obtained from a slaughter-atlases dealing specifically with human house or from animals that were eutha-histology.nized for various reasons. With the excep- Our aim has been to compare the his- tion of smear preparations (blood, bonetologic structure of organs in a variety of marrow, and vaginal), mesenteric spreads,domestic animals. We have used represen-ground bone, and a single plastic section,tative examples in instances where tissuesslides were prepared using the paraffinand organs from different animals share a method. All slides were stained with hema-common structure. Wherever differencestoxylin and eosin unless otherwise noted.exist, we have tried to provide examplesMagnifications of photomicrographs arethat are characteristic of a particular group total magnifications (enlargement of pho-of animals. Our selection of animals in-tograph X objective X projector lens).cludes the dog, cat, horse, cow, sheep, goat, Throughout the atlas, hollow structures,pig, and chicken because they are most fre- for example, blood vessels, kidney tubules,quently referenced in veterinary school cur-and alveoli, are usually identified by label-ricula. ing the lumen of the structure. VIII 9. , Help is often just around the corner. Dr. nary Medicine: Mr. Richard Aucamp andHenry Stempen, whose office was down Mrs. Kathy Aucamp, who provided usthe hall from ours at Rutgers University inwith specimens, slides, advice, and assis-Camden, New Jersey, stopped by one day tance in a variety of other ways; Dr. markand volunteered his artistic talents. Wed Haskins for kindly making available freshlike to thank him for his excellent pen andcanine and feline material; Dr. John Fyfeink drawings of various animal parts,and Dr. Vicki Meyers-Wallen for supplyingwhich are somewhat removed from theus with canine vaginal smears; Dr. andfungi he usually draws. Our gratitude also Mrs. Loren Evans and Dr. David McDevittto Ms. Kathleen Carr for her secretarial for lending us reference material; Dr. Peterservices. Special thanks are extended to Hand and Ms. Graziella Mann for provid-Dr. Edward Zambraski, Ms. Kathleen ing material on the nervous system; and Dr.OHagan, and Ms. Gail Thomas of Cook Helen Acland, Dr. Linda Bachin, Mr.College, Rutgers University, for makingJames Bruce, Dr. Sherrill Davison, Ms.fresh porcine material available to us; andDawn Dowling, Dr. Robert Dyer, Dr.to Dr. Barry Jesse and Dr. James HarnerRobert Eckroade, Dr. George Farnbach,for supplying us with sheep parts. Dr. David Freeman, Dr. Wendy Freeman, Without the unqualified use of the facil- Dr. Alan Kelly, Mr. Joseph McGrane, andities and equipment of the Biology De- Dr. Mary Sommer for their time and con-partment of Rutgers, our tissue processing sideration in helping us to obtain tissue and photomicrography could not havespeClmens.been accomplished. Our special thanks toWe are grateful to Dr. Carol Jacobsonthe Department for this courtesy.and the Department of Anatomy of the This book would never have had a be-Iowa State University College of Veteri-ginning were it not for the generosity of Dr.nary Medicine for providing valuable slideLeon Weiss, Department of Animal Biol- preparations and text material.ogy, University of Pennsylvania School of Our gratitude is also extended to HillsVeterinary Medicine, who invited us to Pet Products, Topeka, Kansas, andteach in the veterinary histology laboratory Pitman-Moore, Inc., Washington Cross-and kindly allowed us access to the slideing, New Jersey, for their generous finan-collection and facilities of the Department. cial assistance.We would also like to express appreciationMany thanks also to: Dr. Carolineto the following individuals from the Uni- Czarnecki of the University of Minnesota,versity of Pennsylvania School of Veteri-College of Veterinary Medicine, for pro-IX 10. viding copies of her informative labora- We are indebted to Mr. William]. Bacha,tory guide; Dr. Deborah Ganster, Dr.Sr., for building a super light box for us,James Lawhead, Dr. Virginia Pierce, Dr. and to Mr. Thomas H. Wood, Jr., for pro-Maria Salvaggio, Dr. Barbara Strock, andviding black and white prints of our pho-Dr. Cindi Ward for assisting us in obtain-tomicrographs, which saved us countlessing tissue samples; Mr. Jeff Bringhurst,hours of drudgery in the darkroom. ThanksBringhurst Brothers, Tansboro, New Jer- to Barbara Frasco, Esq., for her helpful ad-sey, for allowing us access to fresh largevice. Our hats are off also to Snuff, Chew,animal material; the Longenecker Hatch- Chapter Seat, Angel, Clyde, and all theery, Elizabethtown, Pennsylvania, for pro-other animals for their participation.viding chicken specimens; Ms. Susan Ul-We also wish to extend our gratitude torich, Cornell University Press, for lending all at Lippincott Williams & Wilkinsus a difficult-to-obtain reference; the help- whose efforts helped bring this second edi-ful people at Optical Apparatus Company tion into being. We are especially gratefulInc., Ardmore, Pennsylvania, for supplies to Carroll C. Cann and Jennifer D. Weirand for assistance with equipment for the for their professional advice, courtesy,microscope; and to Mr. Charles Behl and and assistance.Mr. James Durso of Webb and CompanyInc., Cherry Hill, New Jersey, for theirWilliam]. Bacha, Jrcourteous service and helpful advice. Linda M. Bachax 11. 1 General Principles of Histology 1 2 Epithelium 9 3 Connective Tissue Proper and Embryonal Connective Tissue 134 Cartilage195 Bone 21 6 Blood 27 7 Bone Marrow 37 8 Muscle41 9 Nervous System4510 Cardiovascular System 5711 Lymphatic System6912 Integument851 3 Digestive System11914 Urinary System 1631 5 Respiratory System17516 Endocrine System 1911 7 Male Reproductive System2031 8 Female Reproductive System22119 The Eye24520 The Ear261 Glossary 269 Bibliography 285 Index287 XI 12. PREPARATION OF HISTOLOGIC SECTIONShistologic section is a thin slice of tissue varying, usually, from 0.5 to 10 or moremicrometers (f-Lm) thick. In preparing such a section, a piece of tissue is either in- with a supporting medium or frozen and is then cut with an instrumentcalled a microtome. Sections obtained from tissue infiltrated with plastic can be as thin as0.5 f-Lm and show superior detaiL Excellent preparations as thin as 2 or 3 f-Lm can also bemade from tissue infiltrated with paraffin-based embedding media. Sections are affixed tomicroscope slides and colored with one or more stains to increase the visibility of variouscellular and intercellular components. Schematically, Figure 1.1 outlines various steps involved in producing a stained his-tologic slide using the paraffin procedure. After being removed from an animal, a tissueor organ is cut into pieces. These pieces are placed into a fixative such as buffered for-malin or Bouins, which, ideally, preserves normal morphology and facilitates further pro-cessing. After fixation, the specimen is dehydrated by transferring it through a series of al-cohols of increasing concentrations to 100% alcohoL Next, it is placed into a substancesuch as xylene, or xylene substitute, which is miscible with both 100% alcohol and paraf-fin. This intermediate step (called clearing) is essential before infiltrating the dehydratedtissue with paraffin because alcohol and paraffin do not mix. During infiltration, meltedparaffin completely replaces the xylene. This procedure is done in an oven at a tempera-ture just above the melting point of the paraffin. When infiltration is complete, the spec-imen is transferred to an embedding mold of fresh paraffin, which is allowed to harden.Then the mold is removed and excess paraffin is trimmed away. The block of paraffin is then secured to the microtome and oriented appropriatelywith respect to the knife. With each revolution of the microtome handle, the specimenmoves through the blade and a section of the desired thickness is produced. Each succes-sive section adheres to the preceding one, forming a continuous ribbon. Subsequently, oneor more sections are carefully separated from the ribbon and transferred to the surface of1 13. o 9. Coverslipping 8. Staining 1. Removing OrganSample 7. Drying on Warmer - - 6. Transferring Sections to Slide 2. Cutting Small Pieces5. Straightening Sectionl1s~_ _~====~ on Waterbath ____.-/ Fix 3. Preparing Specimensfor Sectioning Dehydrate 7 Clear()Embed 4. Sectioning with MicrotomeMold with Specimen Paraffin Block Trimmedin Melted Paraffin Removed from MoldBlock Figure 1.1. The various steps involved in producing a histologic slide using the paraffin method.2 COLOR ATLAS OF VETERINARY HISTOLOGY 14. warm water in a waterbath. This softens the paraffin andThe three-dimensional structure of organs and theirflattens the section, eliminating wrinkles. The flattened sec- components must also be considered when examining a tion is floated onto a slide, which is then placed on a warm- histologic preparation. Cells are three-dimensional objectsing table. As the preparation dries, the section adheres todiffering in size and shape. For example, some are long and the surface of the slide. thin, some cuboidal, and others ovoid. They may have aNext, the paraffin is removed with xylene or another random or specific arrangement within an organ. Howappropriate solvent and the specimen is rehydrated. It isthey appear depends on their shape, as well as how theythen stained, dehydrated, cleared (made transparent) withwere cut. Imagine how the spindle-shaped and tall colum-xylene, covered with a resinous mounting medium, and nar cells shown in Figure 1.2A would look if sectioned intopped with a cover-slip.various planes. Note that the nucleus mayor may not be in- Various stains are available to the histologist. Hema-cluded in a particular cut through a cell.toxylin and eosin (H&E) is a frequently used combinationThe histologist examines multicellular structures hav-of stains. Hematoxylin imparts a purple color to sub-ing a wide variety of shapes. Some are hollow, some branchstances, but must be linked to a metallic salt called a mor- repeatedly, some open onto surfaces, etc. Figure 1.2, Banddant before it can function effectively. This combination, C, and Figure 1.3 show a variety of three-dimensionalcalled a lake, carries a positive charge and behaves as a ba-structures and how they would appear if cut at differentsic (cationic) stain. The lake combines electrostatically with levels. Examine these carefully. They will help you to un-negatively charged radicals such as phosphate groups ofderstand situations you will encounter on actual slides.nucleoproteins. Substances that become colored by a basicstain are said to be basophilic. Methylene blue, toluidineblue, and basic fuchsin are basic stains. Unlike hema-toxylin, these stains have molecules that carry a positivecharge of their own and do not require a mordant. Acidic HELPFUL HINTS(anionic) stains carry a negative charge and color cell or tis-sue components that bear positive charges. Eosin is an acidBe sure that the lenses of your microscope are clean beforestain. It imparts an orange or red color to acidophilic sub- you begin examining slides. Use a piece of lens paper or astances. Other commonly used acid stains are orange G, soft, clean cloth such as an old (but clean) linen handker-phloxine, and aniline blue.chief. If the lenses have been coated with oil or another sub- In addition to the widely used H&E staining proce-stance, remove it using lens tissue moistened sparingly withdure, numerous other stain combinations and techniques a glass cleaner such as Windex. Slides should also beare available. Some are especially useful for identifying cer- cleaned using a soft, lint-free cloth or tissue moistened withtain tissue elements. For example, trichrome proceduresglass cleaner.such as Mallorys and Massons specifically stain collage-Every microscope should have a pointer in the ocular.nous fibers within connective tissue. Orcein and Weigerts This is usually supplied by the manufacturer, but can beresorcin fuchsin are stains used to color elastic fibers, pro- made from a short piece of hair. The latter is cemented intoviding a means of distinguishing them from other fibrous place inside the ocular with a dab of quick-drying glue orelements. Reticular fibers and nervous tissue components nail polish. Without a pointer, it is not possible to accu-such as neurons, myelin, and cells of the neuroglia can be rately indicate an object in the microscope field for anotherstained by procedures employing the use of silver. There observer.are also special histochemical and immunohistochemicalBefore beginning a session at the microscope, makeprocedures that make possible the localization of varioussure that the fine-adjustment knob is near the middle of itscarbohydrates, lipids, and proteins found in tissue. Lastly, range of rotation. If you do not, you may find that the knobstains such as Wrights and Giemsas (Romanovsky stains) is at the limit of its excursion when you are busily makingare available for differentiating the various cells found in observations. At that point, you must stop everything andblood and bone marrow.. correct It.It is also a good habit to examine your slide with the unaided eye before placing it on the stage of your micro- scope. If you do so, you will gain information about theINTERPRETING SECTIONSgross aspects of the specimen and be more likely to center it properly over the light source. Centering is especially im-One must know the gross structure of an organ before a portant for small specimens that might otherwise be diffi-histologic section from it can be comprehended. It is also cult to locate. Also, make sure that you put the slide on thehelpful to know how the section was cut, that is, whetherstage with the cover glass uppermost. If the slide is upsideit was a cross section (x.s.), a longitudinal section (los.), or down, you will not be able to focus on it with the high-an oblique slice through the organ. Was the cut made power lenses. Do not snicker. We have seen this happen of-through the entire organ or only through a portion of it?ten in the teaching laboratory!Frequently, prepared slides are labeled indicating the par- It is always a good idea to start your observations us-ticular orientation of the section. This is not important in ing the lowest power objective available on your micro-an asymmetric organ such as the spleen or liver becausescope. This is usually the 4x lens. The field of view will betheir appearance would be unaffected by the direction of large, enabling you to locate regions of special interestthe cut. Conversely, the small intestine is radially symmet- more easily. When you locate something you wish to ex-ric and its appearance is affected by the direction of the cut.amine at a higher magnification, center the object in theGENERAL PRINCIPLES OF HISTOLOGY3 15. A3 3 4........ . . ... .. .. ..2l2 "~ .,14 :::.:::: :; .. ........ . ,. .., . B 12 3: :/ 45 6l 2 3 00 4 5o 3c2 1 :: ...... ..... ....".. ..-,.......... ......... ........... ...~ .. . ........... ..;.",." ::.. :.,.-:: ...,:,_":~. .. : ........ : ........ ..".... ...... ..: ...-......", . ; .. ",..... , .. ...... " ,. .... ::.. : ........... ... ; . . ...." .. .... . .... ...... ..: .. ....... ;,;".... .....,"....,.. ".. ....... .,. ,......". .-.. -, 32 H $ TEMPEN l Figure 1.2. A. Slices, indicated by numbered planes, taken through two different types of cells would appear as iden - tified by the prime numbers. Only if the plane of the cut passes through the nucleus will the latter be seen. Band C. planes of section taken from different levels in four separate multicellular objects are illustrated. Note how the appear- ance of sections varies with the level of the cut.4 COLO R ATLAS OF VETERINARY HISTOLOGY 16. 2 3 I 3 .- 1 . . . ...; ~o . . .. ... ..;-.:,.o o . : .. .. ..... .. : ... .. . . . . .. , ::;. : . . . . ...o .- . . ~ .. o o , .... . . . .. . . . . . .. . . . .- . . ".. - . . . ". . .. . .. ,. . .. . .. . . . . " .. .. .;....;--ri--1 -- ~ ...:. "- --- .:....:..:.. . .o 2 o.- 5 o o ... .. ::::. o o o o o . .-. , 4 - 6 . : . .. ., o 056 o4 o Figure 1.3. The prime numbers illustrate sections resulting from transverse (4), oblique (1), and longitudinal (2,3,5,6) cuts made through a plate of cells bearin hollow rojections (above late) and invaginations (below plate). plane 3 tion 3appears as a plate of cel s rather than a hollow structure. You shoul also be aware that structures may often appear unrelated to a surface or another object, when in fact they are. Compare planes 5 and 6 with sections 5and 6 , where continuity of the invagination with the surface is evident only in 6 and 6. While not apparent from a single section, such continuity would be evident if an uninterrupted series of sections through the entire invagination were made and examined. GENERAL PRINCIPLES OF HISTOLOGY 5 17. middle of the field of view. Then, when you change to a for your eyes. Be sure that the condenser is raised to itsstronger lens, the object should be somewhere in the field. highest position, or close to it, when you do this. Now, re- Binocular microscopes often have at least one ocular move an ocular and look at the back aperture of the objec-that can be adjusted to accommodate your vision. It is im-tive. Close the aperture diaphragm fully and then open itportant that you adjust this properly if you want to have a until it is about 75% of being fully open. This will providecomfortable, headache-free session at the microscope. As- proper lighting for most purposes. If you should need moresuming that your microscope is of the binocular type andor less illumination, make adjustments only with the rheo-that it has at least one adjustable ocular, you should firststat or neutral density filter; do not use the aperture di-bring the specimen into focus with the ocular that is not ad- aphragm.justable by using the fine adjustment knob. When you haveTo get the most from a specimen, you must avoid be-done this, focus the other eye using the adjustable ocular. ing a passive microscopist, that is, one who finds an objectUse of this procedure will ensure a proper focus for both and then stares at it admiringly without making further ad-eyes and prevent eye strain.justments of the focus. Get into the habit of focusing con- Bright, even lighting is absolutely essential to effective tinuously with the fine adjustment as you peruse a slide, be-microscopy. The best way to achieve this is to use Kohler cause even though a tissue section may be only a fewillumination. This can be obtained with any microscopemicrometers thick, the depth of field of the higher powerthat is equipped with both a condenser aperture diaphragm objectives may be less than the thickness of the specimen.(the one in the condenser) and a field diaphragm (the one Therefore, if you do not focus repeatedly as you examine ain the light source). If you have such an instrument, proceed preparation, you will certainly miss seeing structural detailas follows: that might be important to your work. You might like to return to a particular location on 1. Center the light source, using the directions you re- your slide preparation at a future time. Remembering ceived with the microscope.landmarks in the vicinity of the object of interest will aid 2. Open both the field and aperture diaphragms fully.you in locating the object later. A more expedient way of 3. Raise the condenser to its uppermost position.relocating structures is by using verniers, which are 4. Place a specimen on the stage and focus on it using mounted on both the X and Y axes of the mechanical the lOX objective. stage. A vernier consists of two, parallel, graduated, slid- 5. Close the field diaphragm so that its leaves are clearlying scales, one long and one short. The smaller scale is 9 imaged in the field of view. millimeters (mm) long and is divided into 10 subdivisions 6. Center the image of the diaphragm by manipulating (0 to 10). The larger scale is several centimeters (cm) long the condenser centering screws, then open the fieldand is graduated in millimeters, for example, 0 to 80 or diaphragm until its leaves disappear just beyond the 100 to 160. To relocate an object on a slide, you must first edge of the field of view. center it in the microscope field. Once this has been done, 7. Remove an ocular and, while looking into the back you establish its location by reading each of the verniers (X aperture of the objective, close the aperture di-and Y). For example, the 0 point on the small scale of the aphragm completely and then open it until it is aboutvernier on the X axis might be located somewhere between 75% of being fully open. lines 42 and 43 on the larger scale (Fig. 1.4). To determine You now have Kohler illumination. If you want to in- its specific location, find the line on the small scale that co-crease or decrease the light intensity, use the rheostat or incides exactly with a line on the longer scale. Then count,neutral-density filters, but do not adjust the condenseron the smaller scale, the number of spaces between 0 andaperture diaphragm or field diaphragm. If the aperture di-the point of coincidence. This number is your decimalaphragm is open to excess, the image will lack some con-point. In the example given (Fig. 1.4), the decimal is 0.6trast and be flooded with light. If it is closed too far, there and you should read 42.6 as the vernier value. Do the samewill be a loss of resolution and increase in contrast. This in- for the other vernier (Y) and record the numbers for both.crease in contrast is often confused with sharpness or high In the future, if you want to return to the same location,resolution; this is a common error in microscopy. All of thesimply secure the slide to the mechanical stage and moveabove adjustments (except for centering the light source) the stage controls until the verniers are adjusted to themust be made each time a different objective is used. numbers you previously recorded. These manipulations If your microscope lacks a field diaphragm, you will will have returned the slide to its former position, and thenot be able to obtain Kohler illumination. You can still ac-object you are looking for should be somewhere within thequire good and useful lighting, however. Place a specimen microscope field.on the stage, open the aperture diaphragm fully, and adjustBy knowing the approximate diameter of a red bloodthe light intensity with the rheostat so that it is comfortable cell in a section, you can estimate the size of other tissue Figure 1.4. Small and large vernier scales.405060o106COLOR ATLAS OF VETERINARY HISTOLOGY 18. components. Therefore, it useful to know that in tissue tissues embedded in Paraplast X-TRA (Monoject Scientific,sections prepared by the paraffin method the average size Division of Sherwood Medical, St. Louis, MO 63103).of erythrocytes for each of the following animals is asfollows: Goat 2.4 /Lm diameter (smallest erythrocytes of theARTIFACTS domestic mammals) .Folds, knife marks, stain precipitate, spaces (where none Dog 4.9 /Lm diameter (largest erythrocytes of the do-belong), shrinkage, and air bubbles are examples of com- mestic mammals)monly occurring imperfections seen in slide preparations. Chicken 9.4 mm longThey were introduced during processing and are called ar- Each average value is based on a total of 20 to 30 cells tifacts. Figures 1.5 through 1.9 are examples of such arti-that were measured from five different slide preparations offacts.,GENERAL PRINCIPLES OF HISTOLOGY 7 19. , . .t -- ~ 3":""--- ,Figure 1.5.x 62.5Figure 1.9.x 62.5 KEY1. Dermis4. Knife mark 2. Epidermis5. Separation artifact 3. Fold 6. Stain precipitate Figure 1.5. Stain Precipitate, Cartilage, Dog. Occasionally, solu- tion s accumulate precipitate that may stick to the surface of tissue sections du ring the stai ning procedure. Figure 1.6. Separation (space) Artifact, Skin, Dog. Tissues may be subjected to excessive pressures, tensions, or shrinkage during processing, resulting in separations within otherwise intact tissue. Figure 1.7. Crackling Artifact, Thymus, Horse. Highly cellular tis-Figure 1.6.x 62.5sues, for example, thymus, liver, pancreas, and spleen, often show numerous tiny cracks throughout. Also note that this specimen is not in sharp focus. Figure 1.B. Knife Marks and Folds, Esophagus, Horse (Mas- son /51. Knife marks (scratches) in the tissue section may be caused by defects in the microtome knife or by accumulations of debris on the knife edge. folds occu r when the tissue sections fail to spread properly on the surface of the slide _ Figure 1.9. Fold, Aorta, Pig. In a tissue section, folds are raised areas that frequently overlap. Note that portions of this picture are not in sharp focus .Figure 1.7.x 62.5Figure 1.8. x 25BCOLOR ATLAS OF VETERINARY HISTOLOGY 20. - - he external and internal surfaces of the body and many of its parts are covered byone or more layers of cells. These cellular coverings or linings constitute a tissuecalled epithelium. Epithelial cells are supported by a basement membrane that sep-arates them from the underlying connective tissue. Cells are the principal components ofthe epithelium. Intercellular substance is sparse and is exemplified by the thin layer of ma-terial located between cells, which helps to hold them together. The free surface of ep-ithelial cells may possess cilia, microvilli, or stereocilia.Simple epithelia consist of a single layer of cells. The latter may have a squamous (flat- tened), cuboidal (more or less square), or columnar (tall and rectangular) shape when seen in profile. Pseudostratified columnar, a special category of simple epithelium, appears in profile to consist of several layers of cells. This is an illusion that results from nuclei being located at different levels within cells of different heights. In a sim- ple epithelium, all the cells are in contact with the basement membrane.Stratified epithelia contain two or more layers of cells. Only the bottom-most layer is in contact with the basement membrane. They are classified as stratified squamous, cuboidal, or columnar, depending on the shape of those cells in their outermost (sur- face) layer. A category called transitional is a special form of stratified epithelium lim- ited to the urinary system. The shape of its cells will vary with the amount of fluid pressure applied against it. All glands, endocrine or exocrine, are derived from an epithelium during develop-ment. Numerous examples of glands are presented in subsequent chapters . , 9 21. 7Figure 2.1x 250 Figure 2.5 x 125 KEY 1. Bosal cell 9. Hepatocyte2. Basement membrane10. Lamina proprio3. Columnar cell11. Lymphocyte4. Columnar cell , ciliated 12. Smooth muscle cell5. Connective ti ssue 13. Squamous cell, nucleus6. Cuboidal cell14. strotiRed squamous epithelium7. Esophagus, lumen 15. Striated border8. Goblet cellFigure 2.1. Simple Squamous Epithelium, Mesothelium, Uver,Cat. The surface of the liver is covered by a single layer of squa-mous cells that lie on a thin layer of connective tissue. The cyto-plasm of the squamous cells is sparse and generally only the nu-cleus is visible.Figure 2.2x 250Figure 2.2. Simple Cuboidal Epithelium, Kidney, Cow(Trichrome). The lining of these collecting tubules consists of alayer of cuboidal cells.Figure 2.3. Simple Columnar Epithelium, Jejunum, Dog. The ieiunum is lined by a simple columnar epithelium. A striated border,consisting of numerous microvilli, is evident. Goblet cells and mi -grating lymphocytes are present among the columnar cells.Figure 2.4. Ciliated Pseudostratified Columnar Epithelium, Tra-chea, Cow. In this epithelium the nuclei are at different levels, giv-ing the impression of stratification. All cells, however, contact thebasement membrane.Figure 2.5. Stratified Squamous Epithelium, Nonkeratinized,Esophagus, Cat. Only cells of the basal layer contact the basementmembrane. The name of thi s epithelium is derived from the squa-Figure 2.3x 250 mous cells of its outer layer.Figure 2.4x 25010COLOR ATLAS OF VETERINARY HISTOLOGY 22. -.-, " - - -. - ,, - - -- - , , -- - -- - - ---- -Figure 2.6 .,x 250 Figure 2.10 _ , .x 125KEY 1. Bistralified cuboidal 4. Smooth muscleepithelium5. Stratified columnar epithelium 2. Dermis6. Tronsitional epithelium 3. Keratinized cells Figure 2.6. Stratified Squamous Epithelium, Keratinized, Wat- tle, Pig. The wattl e is covered by a keratinized stratified squamous epithelium . Figure 2.7. Bistratilied Cuboidal Epithelium, Esophagus, Dog. Ducts of glands of the esophagus are lined by a bistratified cuboidal epithelium. Figure 2.8. Stratified Columnar Epithelium, Urethra, Goat. ThisFigure 2.7x 250portion of the urethra is lined by a stratified columnar epithelium. Figure 2.9. Transitional Epithelium, Un stretched, Urinary Blad der, Cat. Surface cells of the transitional epithelial lining are either balloonshoped or broadly cuboidal when not under tension . Figure 2.10. Transitional Epithelium, Stretched, Urinary Blad der, Cat. Surface cells of this epithelium are fiatlened and elan gated when the bladder is full.Figure 2.8x 250 ... , ,. o .0 , . # ... ~ - - _..Figure 2.9x 125EPITHELIUM11 23. onnective tissue binds together and supports other tissues. It is a composite of var-ious cells and fibers in an amorphous ground substance. The latter two compo-nents comprise the extracellular matrix, which typically predominates over the cel-lular elements. The ground substance, composed largely of glycoproteins and glycosaminoglycans,forms a well-hydrated gel that fills the spaces between cells, fibers, and vessels of connec-tive tissue. It acts as a reservoir for interstitial fluid, providing a medium through whichoxygen, nutrients, and metabolic by-products diffuse to and from cells of various tissuesand the vascular system. Collagenous, reticular, and elastic fibers occur in connective tissue. Collagenousfibers, composed of the fibrous protein collagen, are generally the most abundant. Theyare strong and flexible, yet able to resist stretch. They may be fine or coarse, and they arecharacteristically unbranched and somewhat wavy. In tissues stained with H&E, they ap-pear pink and refractile. Reticular fibers are also formed from the protein collagen. Theyare delicate, branching fibers that possess a coat of glycoproteins and proteoglycans. Theyare argyrophilic (silver-loving) and can be stained with silver to distinguish them fromother fibers of the connective tissue. They may also be selectively stained with Schiffsreagent. Elastic fibers, formed from the protein elastin, range in diameter from fine tocoarse and ordinarily cannot be distinguished from collagenous fibers without the use ofspecial stains such as orcein or Weigerts resorcin fuchsin. In some H&E preparations,however, they become colored more intensely by eosin than the collagenous fibers fromwhich they can therefore readily be distinguished. Fibroblasts are generally the most nu-merous of the cells found in connective tissue. They are responsible for the formation ofboth fibers and ground substance. Macrophages (histiocytes), derivatives of monocytes ofthe blood, are also common inhabitants of connective tissue. They are phagocytic cells .that can often be recognized by the presence of debris in their cytoplasm, which givesthem a dirty appearance. Other migrants from the blood that are found in connective tis-sue are neutrophils and eosinophils. Plasma cells, lymphocytes, adipocytes, mast cells, and13 24. globular leukocytes also occur in varying numbers in con-. ~t is helpful to know that there are no sharp lines of dis- nective tlssue. tlllctIOn between loose and dense irregular connective tis- All connective tissues are classified on the basis of thesue, or between dense irregular and regular connective tis-arrangement and proportions of their cellular and intercel- sue. It is n~t always possible therefore to classify these typeslular components. Connective tissue proper includes the of connectlve tlssues with great precision.general types of connective tissue, loose and dense as wellas the special types, reticular, elastic, and adipo;e. Mes-Reticular tissue is composed of numerous reticularenchyme and mucous connective tissue are classified as em-fibers. It forms a supportive network for thebryonal connective tissues. parenchyma of structures such as the spleen lymphnode, liver, kidney, and bone marrow. In loose (areolar) connective tissue, the ground sub- Elastic tissue is characterized by numerous regularly orstance predominates. It contains many scattered cells oflffeg~larly arranged elastic fibers. It is exemplified byvarious types, vessels, and a loose network of fine collage-nous, retlCular, and elastic fibers. Loose connective tissue is the lIgamentum nuchae of grazing animals and by thevocal ligaments.widespread throughout the body. It surrounds vessels andnerves. It is found in serous membranes such as mesenter-Adipose ti.ssue consists of groups of adipocytes (alsoies, the lamina propria of mucous membranes subcuta-called adIpose cells or fat cells) within the loose con-neous tissue, and the papillary (superficial) layer ~f the der- nective tissue of such places as mesenteries , subcutis ,and sheaths of vessels and nerves.mis, as well as other places. In contrast to loose connective tissue dense connective Mesenchyme tissue is found in the embryo. It consists oftissue. (often called fibrous tissue) is co~posed principallya loose arrangement of pale, star-shaped (stellate) cellswith interconnecting cytoplasmic processes. The mes-of thIck collagenous fibers. It contains fewer cells thanloose connective tissue, most of which are fibroblasts. Inenchyme cells are embedded in a jellylike, amorphous,dense irregular connective tissue, the collagenous fibers ground substance that accumulates fine fibers as devel-course in all directions, forming a compact three-dimen-opment progresses.SIOnal meshwork. Dense regular connective tissue is char-Mucous con~ective tissue, another type of embryonalconnectlve tIssue, surrounds the vessels of the umbili-a.cterized by closely packed, parallel bundles of collagenousflbers. Dense Irregular connective tissue occurs in suchcal cord. It also occurs in limited regions in adult ani-places as the reticular (deep) layer of the dermis, the sub-mals, for instance, the dermis of the comb and wattlemucosa of the digestive tract of some species, and the cap- of the chicken. It is composed of fibroblasts andsules of organs. Tendons, ligaments, and aponeuroses areloosely arranged, fine, collagenous fibers in an abun-formed by dense regular connective tissue.dant, amorphous ground substance.14 COLOR ATLAS OF VETERINARY HISTOLOGY 25. - - fi- - .-, , I~ f -7f .. ~ ,,.4 " .,- ~" , ,. .....~~ ,-, ...-1 ,J- ~,-9 }. .. 10-.~;_7 --9 " IFigure 3.1 ~x 250Figure 3.5- x 625 ,, ~ ... -KEY -, . r,~ 1. Amorphous ground substance7. Fibroblast nucleus , , ., -t; 7.,..., - ~ -I. - . 2. Collagenous fiber 3. Elastic ~ber8. lymphocyte9. Mast cell -4. Eosinophil10. Mesenchyme cellt - - 5. Epithelium, lip 6. Erylhrocytes in cap;Uary11 . Neutrophil12. Plasma cell - tI , r ----. 2. ,, , .,I , . J.;Figure 3.1 . Mesenchyme. 72-Hour Embryo. Chicken. Mes-, , , ..L,~... ...J1, ...., ". o, J_/ , ,, , ,f,- -, - r-( - { ...., / -< ,.--I , 1 " - , ; / I - ,II " , ... A / 1" ,Figure 3.11 x 125 Figure 3.15x 62.5KEY1. Adipocyte5. Reticular fiber2. Elastic fiber6. Tendon, x. s.3. Fibroblast nucleus 7. Tendon sheath, inner4. Lymphocyte 8. Tendon sheath, outer" f, ~, .Figure 3.11. Tendon and Tendon Sheath, x.s., Dog. The tendonsheath is actually made up of two sheaths. The inner sheath at-taches to the sur.ace of the tendon. The outer sheath forms a tubearound the tendon and attaches to peripheral structures. Thespace between the two sheaths is filled with synovial fluid in livingtissue. The space is not lined by an epithelium, but rather by col-lagenous fibers and cells of the connective tissue of the sheaths.Figure 3.12 x 62 .5 Figure 3.12. Elastic Tissue, Ligamentum Nuchae, I.s., Sheep., This section shows the parallel arrangement of the elastic fibers ,... ~ ." within the ligament.~(~ .. Figure 3.13. Elastic Tissue, Ligamentum Nuchae, x.s., Sheep,.-,. J (Orcein). Orcein selectively stains elastic fibers red.. Figure 3.14. Reticular Tissue, Lymph Node, Cow (Silver). Net-works of reticular fibers have been blackened by silver.Figure 3.15. Adipose Tissue, Soft Palate, Cow. Lipid content ofeach adipocyte (unilocular) was removed during processing, leav-ing an empty cavity surrounded by a thin rim o. cytoplasm. Nucleioccur at the periphery of adipocytes. It is sometimes difficult to dis-tinguish their nuclei .rom those of other cells of the connective tis-sue. See Figure 12.104 for an example of multilocular adipocytes.Figure 3.13 x 62 .5Figure 3.14 x 25018COL ATLAS OF VETERINARY HISTOLOGY OR 29. ,--.., artil age is a fo rm of connecti ve tiss ue. There are three basic types of cartil age: hya-line, elastic, and fibrous (fib roca rtilage). Each consists of chondrocytes embedded~ in an a mo rph o us, grou nd substance (matri x ), w hich is ti ch in sulfated gly-cosaminoglycans complexed with protein to fo rm macromolec ules called proteoglyca ns.The latter a te bo und electrostatica lly ro unit fibrils of collagen. The matrix is firm butfl exible. Hyaline cartilage is th e most common rype. It forms large parts of the developing ver-tebrate skeleton, and it is also fo und in epiphysea l discs, articular cartilages, the tra-chea, bronchi, an d elsewhere. Its ground subsrance is separable into pale and darkl ystained areas called interterritorial and territorial matrix, respectively. The higherconcentrati o n of sulfated glycosa minoglycans in rhe larrer is responsible fo r rh edarker sta ining. Chondrocytes a re confined to sma ll spaces (lacunae) within th e ma-trix. Small cl usters of chondrocytes, ca lled isogenous groups, a re frequentl y o bserved .They are the res ult of cell di vision of chond rocy tes. Cartilage matrix is usuall y in-ves ted by a perichondrium whose inner la yer is chondrogenic, containing cells withthe capacity to become chondroblasrs. Its outer portion is dense irregular connecti ve .tissue. Elastic cartilage is similar in structure to hya line ca rtilage. Its na me derives from thepresence of large amounts of elastic fibers embedded in the matrix . Amo ng oth erplaces, it is fo und in th e ep iglottis, parts of the larynx, and the pinna . Fibrous cartilage is unlike either of the other types. It is dense connective tissue withinwhich are distributed linear groupings of chondrocytes embedded in a small amOllntof matr ix. Fibrous cartilage is found in such places as the intervertebral discs and car-diac skeleton, as well as w ithin some tendons close to their attachment to bone. 19 30. KEY 1. Chondcocyte6. Matrix 2. Chondr~ein lacuna7. Perichondrium, chondrogenic 3. Collagenou~ fiber8. Perichondrium, fibrou~ 4. Elastic fiber9. Territorial matrix 5. Interterritorial matrixFigure 4.1. Hyaline Cartilage, Trachea, Cow. The perichondriumconsists of an outer fibrous and an inner chondrogenic layer.Isogenous groups and single chondrocytes are scattered through -out the matrix..Figure 4.2. Elastic Cartilage, Epiglottis, Dog. Pink elastic fiberscan be seen throughout the cartilage matrix.Figure 4.2x 250Figure 4.3. Elastic Cartilage, Wattle, Pig (Orcein). The elasticfibers are stained red with orcein .Figure 4.4. Fibrocartilage, Intervertebral Disc, Horse. Chondro-cytes are arranged in rows and framed by a hazy rim of pale bluematrix. C~lIagenous fibers are visible between rows of chondrocytes.Figure 4.5. Fibrocartilage, Claw, Chicken. Rows of chondrocytesare randomly scattered among collagenous fibers. Pale blue ma-trix is visible around some chondrocytes.Figure 4.3x 125 ..:# ..x 125, .Figure 4.420COLOR ATlAS OF VETERINARY HISTOLOGY 31. one is a livin g, dynamic connective tissue. Its hardness and strength are p rovided by a matrix consisting of hydroxyapa tites and collage n, respectively. It is admirably sui ted to its function as a skeleta l substance because of its high tensi le strength andrelatively light weight. The structure of bone is unrelated to its mode of develop ment; tha t is, the lamellae ofintramembranous bone have the same basic str ucture as thnse of endochondral (in-tracartilaginous) bone. Mature bone, however, contains fewer osteocytes tha n the imma-tu re bone it replaces. The woven fo rm of the latter contains n um~rous osteocytes and anorga nic mat.ri x of interlacing collageno us fibe rs. Its ma trix has a bl uish cast in prepara-tions stained with hematoxyli n and eosin. In contrast, the matrix of mature bone is un i-fo rmly acidoph ilic . ..Deposits of matrix may be dense, with few spaces between matrix elements (compactbone), or they may be in the fo rm of delicate three-dimensiona l latticeworks (spongybone) . Compact bone forms the outer shells of the diaphysis and epiphysis, while spongybone occurs in the interior of the epiphysis and the endosteal surface of portions of the di-aphysis. In the compact bone of the diap hysis, matrix appears as haversian systems, in-terstitial systems, a nd circumferentiallamel1ae.Altho ugh osteocytes are entrapped with in matr ix, they a re a ble to communicatephysically th rough canaliculi, whic h connect lac unae with each other. Osteoblasts a nd os-teoclasts lie free on the external surface of the matr ix. T he former secrete most of the ma-trix and eventua ll y become surrounded by it. They are then called osteocytes. Osteoclasts,large multi nuclea te cells de rived from monocytes, resorb matrix durin g bone remodelingor when the need for serum calcium arises. Bone matrix undergoes remarkable tra nsformations in size and sha pe dur ing devel-opment, T his process of bone re modeling is especia ll y well exemplified dur ing the for-mation of the skull and long bones. In both instances, transforma tions in shape and in-creases in size are accomplished through the processes of bone deposi tion and boneresor ption .An im porta nt aspect of the growth in length of long bones is the persistence of fu nc-tional epiphysea l discs. These plates of hyal ine cartilage perm it the process of intracarti-laginous ossification to cont.inue unt il full growth of the bone is ach ieved, at whic h timethe discs become replaced by bone and no furt her lengthening is possible. 21 32. ~-...-~:.... ....... :-~"1,/ ; ;4 . r:; .... _. __ "..7-7-"""< ~- .,. " """ . . -, ,"t,""....! lFigure 5.3 x 62.5"",,.. ... .. , .,""... ,"... .... .-." ,""" ,::... ,.,., ...... . . .. . oJ. . .... ,..... .. .- . ........ ~/.............. ~:"" . ...... ...... ". ....:",,-.,., ....... -.:"",", -~.,.,"::.:" y .::: . /.;.:- .. . ,"., ... . " :..:."::~".;., , " 1" )... ~~ ...:., ,."3.4.5.Central canalfluidfilled spoceGlycogen body 11. 12. 13. Nucleor bag fiber Nuclear chain fiber Outer core , . : oi II . . , ~ "~Ii ,:~~ .-::.:. ;!f.,,:.,!..~,~ i .~.~: &~~.o1;:.~ ..,j,:, ~,.~~. r, I"(;t , .. :" ,,. ;; ., ~~ f!~;" _,.or, . :f ~, .... , I i""X :I"F..,...~,..Q ... ..,.. , " .., ( .. ; , . 1 "":1 ........,- , !1!,$~~1: ,.... ... "Y , ~~- ..r ti;.f k... " "."Figure 9.32 x 62.5 Figure 9.36x 62.5 .. , ,KEY 1. Axon10. Muscle (moves feather)2. Bone11 .Gray matter ,3. Copsule of Herbst corpuscle 12. Multipolar neuron 154. Cell of glycogen body 13, Nerve , 5. Central canol6. Core 14. 15. Sharpey, fibers Space artifact , , 7. Dermis16. Unipolar neuron8. Dorsal root ganglion17. Ventral root , . -9. Epidermis 18. While maHer,. Figure 9.32. Glycogen Body, lumbosacral Enlargement, Spinal I Cord, x.s;, Chicken. Cells of the glycogen body in detail. See Fig ure 9.31 tor description.Figure 9.33 x 12.5 Figure 9.33. Dorsal Root Ganglion, lumbosacral Enlargement, Sr inal Cord, X.S. , Chicken. Portions of the spinal cord, ventral root o a spinal nerve, dorsal root ganglion , and vertebra. Figure 9.34. Dorsal Root Ganglion, lumbosacral Enlargement, Spinal Cord, x.s., Chicken. Neuron cell bodies of unipolar neu. ~:. rons and myelinated axons are shown. Figure 9.35. Herbst Corpuscle, Up~r Beak, x.s., Chicken. These encapsulated nerve endings occur frequently in the skin of the bird . They are similar to pacinian corpuscles of mammals and consist of an outer capsule of connective tissue, a laminated core, , and an axial sensory nerve ending. Figure 9.36. Herbst Corpuscle, Skin, Neck, Chicken. The Herb,t corpuscles associated with follicles of feathered skin are sausage- shaped.Figure 9.34 x 62.5Figure 9.35x 125 NERVOUS SYSTEM 55 66. ""1he heart pumps blood and conveys it to the tiss ues and organs rhrough blood ves- sels. Fluid rhat escapes from the blood is retu rn ed to the veno us system by lym- phatic vessels. Vessels of rhe cardiovascu lar sysrem are lined by an endothelium, which is, typica ll y,a single la yer of squamous cells. The smallest of the blood vessels, capillaries, are tin y en-dothelia l tubes . They are easily overlooked in histologic secrions, especiall y if rhey arecompressed or collapsed. The walls of arteries and veins are arranged into concentric la yers: the inner tunicaintima, middle tunka media, and o uter tunica adventitia. The compositi o n and th icknessof these layers vary wit h the size and type of vessel. The tun ica media is nor always pre-sent.Small arteries can be defi ned, arbitrari ly, as possessing up to eight or nine layers ofsmooth muscle cells in the tun ica media. The smallest of these vessels is usually termed anarteriole. Irs wall is composed of an endotheli um (tunica intima), one or two layers of c ir-cu larl y arranged smooth muscle cell s (tu nica media) , and a bit o f surround ing loose con-necti ve ti ssue (tunica adventitia). Some of rhe larger small arteries have an internal elasticmembrane. Small arteries are acco mpa nied by small veins. The sma llest veins a re calledven ules. These are simi lar to arteri o les, but have relativel y thin wall s and lack a tu nica me-dia of smooth muscle. An internal e lastic membrane is not fo und in small veins.As the diameter of a vessel increases, the tun ics become larger and more elaborate.For examp le, th e tun ica intima of a medium artery contains connective tissue interspersedbetween the endothelium and internal elastic membrane. The thick tunica media, withvarying proportions of smooth muscle and elastic fibers, comprises the bulk of the wall.The connect ive ti ssue o f th e tun ica advent itia contains co llagenous and elas tic fibers,small blood vessels (vasa vasorum ), and nerves. A medium vein, in contrast, has lesssmooth muscle and fewer elastic fibers in the ru nica media and possesses a thi cker tu nicaad ve ntitia.Arteries ordinari ly appea r round in cross section and have an obvious, rippled, inter-na l elastic membrane. Conversel y, acco mpan ying veins are larger in diam eter with an ir- 57 67. regu lar or collapsed lumen and th inner wa lls, and, exceptMany special vessels un iq ue to certain organs such asfor some of the largest, they have no internal elastic mem- the sinusoids of the liver, postcapilla ry venu les of lymp hbrane. T he lu mens of blood vessels in tissue sections often nodes, and helicine arte ries of the penis a re presented else-conta in blood cells, plasma, or both. Although it can be dif-where with their appropriate organ systems.ficult to distingu ish between veins and lymphati c vessels,The heart is a muscu la r organ whose wall is composedthe latter have thinner wa U tha n veins of simi.lar size ands of an endocardium, myocardium, and epicar d ium . Thenormally do not contain erythrocytes. Valves may occur in thick ness and composition of the wa ll vary, being thickestboth veins a nd lymphatic vessels.in the ventricles and thi nnest in the atria . T he middle layer There are several variat ions fro m the "typical" bloodof card iac muscle, the myocardi um, predominates . Valvesvessels: T he tun ica adventitia of large veins adjacent to the of connective tiss ue covered by an endothel ium, are exten-heart contains cardiac, rather than smooth, muscle. Somesions of the endocard ium . Regions of the heart, incl udi ngarteries have smooth muscle in the tu nica intima, as we ll asthe base of the aorta and pulmonary tr unk, as well as thethe tunica media. Smooth muscle may be oriented eitheratr ioventricular orifices and septum, a re supported by thelongitudina ll y or circ ul arl y. T he tu nica adventi tia of arter- cardiac skeleton. T his cardiac skeleton may be in the formies may be either ab unda nt or scam .of dense irregular connective tiss ue, fibrocart.ilage, hyal ine The arteries of arterioveno us an astomoses lac k an in- carrilage, .or bone and va ries with age and among ind ivid-ternal elastic membrane, but possess epithelioid (epithelial- ua ls.like) longitud inall y a rranged smooth muscle cells. Specia lA small amount of fl uid occurs in the pericard ial cav-structures, the aortic and carotid bodies, are closely associ-ity between the epicardium (viscera l perica rd iu m) and theated with the tun ica adventitia of their respective arteries.pa rietal pericardi um . 58COLOR ATlAS OF VETERINARY HISTOLOGY 68. :.....- 4 . , - .. .. ~ ,6/ ~, .. 10 - lO , . ... ... .....< s,. """ 10 -Figure 10.1 X 250 Figure 10.5 X 250KEY1. Arteriole, x.s.9. plasma cell2. (opilimy, I.s.10. Skeletal muscle cell, x.s.3. Capillary, x.s. 11 . Small artery, x.s.4. Endothelial cell, nucleus 12. Small vein4--5. Endothelial cell, surface cut 13. Smooth muscle cell , nucleus6. Erythrocytes14. Uterine gland7. Macrophage15. Venule8. Mast cellFigure 10.1. Capillaries, x.s. and I.s., Diaphragm, Dog. Exten-sive capillary networks occur around muscle cells.Figure 10.2. Capillary, I.s., Lamina Propria, Duodenum, Sheep.Erythrocytes fill the lumen of this capillary.Figure 10.2 X 625Figure 10.3. Arterioles and Venules, Eyelid, Pig. Small blood--- vessels of various sizes are present in the dermis.Figure 10.4. Arterioles, x.s., Endometrium, Uterus, Dog. Thesmallest of the arterioles shown have only one layer of smooth muscle in their walls.;CyOes 10. Meaullmy card 11 . Medullary sinus 12. Megakaryocyte 8 6. Granulocyte 13. Reticular cell7. Lymphatic nodule14. Subcapsular sinus1311., t- Figure 11.31 . Medulla, Lymph Node, Dog. Cell ular medullarycords surround medu llary sinuses that are lined incompletely byendothelial cells. A megakaryocyte is present in a medu llary cord. Figure 11 .32. Medulla, Lymph Node, Dog. Macrophoges con-taining phogocytized erythrocytes ore evident in the medullary si-nuses.Figure 11.33. Hemal Node, Sheep. The general organization ismuch li ke that of a lymph node, but the sinuses are filled withblood. Lymphatic nodules are scarce, and trabeculae of connec- tive tissue are not apparent .Figure 11 .34. Hemal Node, Sheep. The subcapsula r (ma rginoll sinus is fil led with blood. Reticular cells of the sinus contain p~agocytjzed material. 1Figure 11 .33x 25 87. 1-Figure 11 .35Figure 11.39 x 62 .5 KEY1. Capsule7. Mesothelium 2. Central artery8. Red pulp 3. Ellipsoid 9. Trabecula 4. Endothelial cell 10. Venous sinus 5. Lymphatic nodule 11. White pulp 6. Marginal zone Figure 11.35. Spleen, Dog. This drawing is of a small portion of the spleen. Figure 11.36. Spleen, Dog. The parenchyma of the spleen is or- ganized into red pulp and white pulp (periarterial lymphatic sheaths and lymphatic nodules). Trabeculae extend inward from the capsule and are seen throughout the red pulp.Figure 11.36 x 12.5 Figure 11.37. Spleen, Dog. Note the smooth muscle in the cap sule and trabeculae. The spleen of the dog is a sinusal spleen, con- taining venous sinuses (see Fig. 11 .38 ). Figure 11.38. Spleen, Dog. Venous sinuses are lined by longitu- dinally oriented, elongated endothelial cells. The nuclei mayor may not be apparent in cross sections of such lining cells. Ery- throcytes fill the sinuses and the spaces of the red pulp. Figure 11.39. Spleen, Dog. Ellipsoids can be seen in the marginal zone between the periarterial lymphatic sheath (white pulp) and the red pulp. They are also present in the red pulp.Figure 11 .37x 62 .510Figure 11.38 x 250 LYMPHATIC SYSTEM 79 88. Figure 11 .40x 125Figure 11.41 x 25 .. _ ..!~" !..,..tl: Figure 11.44x 62.5 ,~. - ....... _.... .,- ,.-... .. .. - I. Capillary lumenKEY 7. Periarterial lymphatic sheath. .. . , . I.... .. 2. Capsule8. Red pulp3. Central Artery 9. Serosa -- -- --- -4. Elastic fiber I O. Smooth muscle- - -- --....-.. 5. Ell;pso;d II. Trabecula -.. - . . . .. -- -: i~ ...... ~ 6. Marginal zone Figure 11.40. Spleen, Pig (Orcein). The capsule and trabeculae.... "are rich in elastic fibers (redbrown).Figure 11.41. Spleen, Pig (Mallorys). Ellipsoids are abundant inFigure 11 .42x 62.5 the pig. They are especially numerous in the vic inity of themarginal zone of a periarterial lymphatic sheath. See Figure11 .44 for details of ellipsoids.-. .- -FiBure 11.42. Capsule, Spleen, Horse. The capsule of the spleenof the horse and cow contains layers of smooth muscle oriented at .- - . , . . ..- .. .. . . . . ., - - ,J ~ :. " .- 0 .- - r . . ..,. . . . .,- . - ". . -_ ", "right angles to each other, rather than being interwoven as in car-nivores, pigs, sheep, and goats. In thi s preparation there are three .-.. . "distinct layers of muscle. Compare with Figures 11 .37, 11.43, and11.45 . .. . . ". .. . . . .,.. -, - ....... ...- Figure 11.43. Capsule, Spleen, Cow. The capsule contains two... ..., .. --.-.-.-,........ .. ..." . .~~->:.-.":""thick layers of smooth muscle oriented at right angles to each..other.Figure 11.44. Spleen, Pig. Ellipsoids are especially abundant inthe spleen of the pig. Each consists of macrophages and reticularfibers that surround a capillary.figure 11.43 X62.580 COLOR ATlAS OF VffiRINARY HISTOLOGY 89. - KEY .-. .... ,. . ,.._..,. . .::1. .. .... . ....~.~.. ... . - ,."-~ -- .~ 1. Capsule 2. Cortex7. Septum8. Serosa.-".- .!:~--~~-. -. --, 3. Elastic fiber9. Smooth mu~le -~4. Lymphatic vessel 10. Trabecula~-~5. MedullaII . White pulp6. Red pulpFigure 11.45. Capsule, Spleen, Sheep. In sheep the bulk of thecapsule contains many interwoven smooth muscle cells. Thesmooth muscle in the capsule of the spleen of carnivores Isee Fig.11 .37L pigs, and goats has a similar arrangement. In the horseIsee Fig. 11 .42) and cow Isee Fig. 11 .43) the muscle cells are ar-ranged in layers instead. Elastic fibers can be observed as faintpink spirals.Figure 11.45x 62 .5Figure 11.46. Spleen, Sheep. Note the thick trabecula. Charac-teristically, the spleens of cows and sheep have thick trabeculae.Compare with Figure 11 .4 1.Figure 11.47. Red Pulp, Spleen, Sheep. Wisps of smooth musclea re scaHered throughout the red pulp.Figure 11.48. Thymus, Puppy. A thin capsule of connective tissuecovers the thymus. Lobules, incompletely divided by connective-tis-sue septa, consist of an outer, dark cortex and an inner, palemedulla . The medulla is continuous between adjacent lobules.Figure 11.46x 25Figure 11 .47 x 125Figure 11.48x 12.5LYMPHATIC SYSTEM 81 90. Figure 11.49KEY 1. Cortex3. Medulla2. Hassolls corpuscleFigure 11.49. Thymus, Puppy. Portion of the medulla and cortex.The cortex consists predominantly of small lymphocytes. The lym-phocytes of the medulla are larger and less abundant. Themedulla contains concentrically arranged , swollen, and keratinized reticular cells that form Hassalls corpuscles, which arecharacteristic of the thymus .82COLOR ATLAS OF VETERINARY HISTOLOGY 91. , 1, . "- 1-.-.--.. ,., ,tFigure 12.49. Mammary Gland, Inactive, Cow. Lobules arecomposed of intralobular ducts and intralobular connective tissue, " ", :-: ., which is moderately rich in cell s. Thickenings at the terminations of .. intralobular ducts represent remnants or precursors of glandularepithelium. When these are cut in cross section, they cannot al-ways be distinguished from ducts.Figure 12.50. Mammary Gland, Active, Cow. In the activeFigure 12.48 x 25 gland, secretory parenchyma is well developed and connective tis-; jrF. J csue is reduced. Compare with Figure 12.48. The lumens of the secretory glands and ducts are fi lled with secretion (deep pink)....."",-,.,,. r- ,1 6 -_. -. -. ,I- ,~.~ J ,. .Figure 12.49 x l25102COL ATLAS OF VETERINARY HISTOLOGY OR 111. " ..} ..y~ . f. ".." ~.~ ... ~~~- Figure 12.51 x l25Figure 12.55x 12.5~~ -; KEY II~I . Connective tissue7. Secretory cen, nucleus.",2.Corpora omylaceo 8. Secretory unitt 3. Epidermis 9. Smooth muscle 4) 4. Intralobular connective tissue 10. Sweat gland5. Myoepithelial cell, nucleusII. Teot sinus6. SecretionFigure 12.51. Mammary Gland, Active, Cow. A portion of a lob-ule containing numerous tubuloacinar secretory units. Some of thealveoli contain round concretions of casein and cellular debriscalled corpora amylacea.Figure 12.52. Mammary Gland, Active, Cow. Many secretorycells have basally displaced nuclei and indistinct lateral cell bor-Figure 12.52 x 250ders. These cells appear pale because th eir cytoplasmic lipidshave been extracted. Sloughed cells, whose dork nuclei a re vis iblein the lumens, are part of the secretory product. Some of the flatnuclei su rrounding the alveoli belong to myoepithelial cells.Figure 12.53. Teot, x.s., Dog. A portion of the teat shows nu-merous si nuses among intermingling bundles of smooth muscleand fibroelastic connective tissue. Nonruminants have multipleteat sinuses and teat canals. Some glands and hairs are associ-ated with the skin of the teat of carnivores, horses, sheep, andgoats.Figure 12.54. Teot Sinus, x.s., Dog. Detoil of a teat si nus of Fig-ure 12.53 reveals a hi ghly folded lining. Glandular areos, com-posed of small secretory units, are associated with the wall of the smus.Figure 12.55. Teat Sinus, x.s., Cot. This cross section through aFigure 12.53 x 12.5 teat reveals five teat sinuses. Some of these contain a secretion that ~"f! . )"J is stained pink. " I I, " -"",,- "j. "". ... ....l.- i~ ., ," .7.~...,.., . .. . ... 1 , ~ " t~~ .~ I I , .".i" Ii .I " ~ll I f igure 12.54x 62.5 INTEGUMENT103 112. ,-L _Figure 12.56x 125Figure 12.59x 25KEY 1. Bistroti fied columnar epithelium 8. Hair follicle 2. Bistroti fied cuboidal epithelium 9, Lamina propria 3. B ve55el lood 10. Lymphatic vessel 4. Collagenous bandII. Sebaceous gland 5. Elastic fi bers 12. Smooth muscle 6. Epidermis 13. Sweot gland 7. Epithelium14. Teat sinus Figure 12.56. Teat Sinus, x.s., Horse (Orcein). A band of col- lagenous fibers lies befween the epitheli um and the underlyi ng fi broelastic connective tissue. Figure 12.57. Teat Sinus, x.s., Cow. The mucosa of the teat sinus blends with the middle layer of the teat. The latter contai ns well-Figure 12.57x 12.5 developed, longitudi nally oriented blood vessels (cut in x.s.); bun- d les a t smooth muscle; fibroelastic tissue; and lymphatic vessels. The outer layer, the ski n su rface, is not shown. Figure 12.58. Teot Sinus, x.s., Cow. The teat si nus is lined by a bistratified cuboi dal to columnar epithelium. Figure 12.59. Teot Sinus, x.s., Sheep, Male. The ski n of the teat 14conta ins ha irs, sebaceous gla nds, a nd sweat glands, except in the cow a nd pig. Compare with Figu re 12.63. / 2 ___ 1Figure 12.58x 180 113. KEY 1. Bistratified columnar epithelium8. Smooth muscle 2. Bistratified cuboidal epithelium9. Strati fied squamous 3. Blood vessel epithelium 4. Dermis 10. Stratum basale 5. Epidermis11. Stratum corneum 6. Epithelium 12. Stratum spinosum 7. Lamina proprio Figure 12.60. Teat Sinus and Canal, Junction, x.s., Horse. Patches of the bistratified epithelium (columnar and cuboidal) of th e teat si nus intermingle with the stratified squamous epithelium of the teat canal. Figure 12,61 , Teat Canal, x.s., Cow (Trichrome). The keratinizedFigure 12.60x 62.5 stratified squamous lining of the teat canal is encircled by a papil- lated layer (green) of connective tissue and bundles of smooth muscle {pa le yellow}..Figure 12,62, Teat Canal, x.s., Cow (Trichrome). Detail of the.~ thick keratinized stratified sq uamous epitheli um and the surround- ing connective tissue and smooth muscle shown in Figure 12.61 .,Figure 12.63. Skin Surface, Teat, x,s" Cow (Trichrome), The ski n su rface of the teat of the cow and pig is hairless., .....~I.tf.. ,Figure 12.61 IFigure 12.62figure 12,63 x 25INTEGUMENT105 114. , .- 11710Figure 12.64x 26 KEYI. Claw fold7.limiting Furrow 2. Dermis8.Merocrine sweat gland 3. Digital pod 9.Middle phalanx 4. Distal phalanx 10.Sole 5. Epidermis, digital pad I I. Wall 6. laminae Figure 12.64. Developing Claw, I.,., Fetu" Dog. The claw of car- nivores consists of a dorsal and lateral wall (body, claw plate) and a ventral sale of hard keratin that cover the distal pha lanx. The claw fold is the skin that covers the wall at the base of the claw. Endochondral bone formation has begun in the phalanges of this10 specimen .Figure 12.65x 12.5 Figure 12.65. Sale of Claw and Digital Pad, Dog. The limiting furrow separates the digital pad from the sale of the claw.11 Figure 12.66. Apex of Claw, I.,., Dog. The dermis of the wall bears laminae (lamellae) at the apex of the claw. -, " ,- . , Figure 12.66 -..x 12.5106COL ATLAS OF VETERINARY HISTOLOGY OR 115. IKEYl. Dermal papilla 6. Strotum basole~ 2. Dermis 7. Stratum corneum3. Hair follicle8. Stratum granulosum6) 4. Horn tubule 9. Stratum spinosum }5. Intertubular horn 72 IFigure 12.67. Horn, Cow. Horns of ruminants are composed of., j I bone ofthe cornual process covered by a dermis and epidermis. ( I.j .The epidermis wilh a thick slratum corneum of hard keralin (hornl, and a portion of the underlying papillated dermis are shown here. (Photograph of a histologic section borrowed from the College of jVeterinary Medicine, Iowa State University.) Figure 12.68. Chestnut, Horse. Junction of the hoiry skin ondFigure 12.67x 12.5chestnut. Chestnuts (ond ergotsl of horses are keratini zed thickenings of the epidermis composed of horn tubules (tubula r horn I andintertubular horn. Horn tubules arise from the cell s of the stratu mbosale thot cover the apex ond sides of dermal papilloe. Intertubular linterpapillory) horn arises from the cells ot the stratumbasale that are located between the bases of the dermal papillae.Only a small portion of the very thick stratum corneum of the chestnut is shown.Figure 12.69. Chestnut, Horse. Detail of a portion of the epidermls.Figure 12.70. Chestnut, Horse. The section was cut parallel to thesu rface of the chestn ut at the level of the stratum corneum. Horntubu les appear in cross section between intertubular horn.Figure 12.68x 12.5Figure 12.69x 62.5.- ,..5Figure 12.70x 125 INTEGUMENT 107 116. The equ ine hoof is th e keratinized portion of the epi-is characterized by the presence of fine, short papillae (1 todermis that covers the distal end of the digit. The various2 mm ).regions of t he hoof are dep icted in Figures 12.71 a ndThe germinal cells of the coronary epidermis form12 .72. The perioplic, coronary, and laminar regions com-horn tubules (tubular ho rn ) and intertubular horn t hat ex-prise the wa ll (the portion of the hoof that is visible whentend from the coronary region to the ground su rface, form-the d igit is on the grou nd ). The wall turns in ventrall y at an ing the bulk of the wa ll of th e hoof, the stratum medi um.acure angle to form the bars. The sole, w hich forms most of The horn tubules are oriented at an angle to the ground.the ventra l su rface of the hoof, is attached to the bars and They parallel the extern al surface of the hoof. The coro-the ad jacent, inner border of the wa ll. The frog, a cauda l, nary dermis is marked by long dermal papillae (4 to 6 mm ).wedge-s haped mass, lies between th e bars. The apex of the The laminar epidermis of the wa ll is in the form o f lam-frog merges with the sole craniall y. T he bulbs are the con-inae (lamell ae) that are arranged pa rall el to th e hornvex protuberances located above and behind th e frog.tubu les o f th e st rarum mediu m. They extend from th e deepThe kerat inized tissue comprising the hoof is in theedge o f th e coro na ry reg ion to th e sole. Each primary lam-form of tubular, intercubular, and lamin a.r horn (see Figs. ina bea rs nu merous secondary laminae (not presen t in th e12.75, 12.76, 12.79, a nd 12.80) . The underly ing, living hooves of pigs and rumi nants) that project at right angleslayers of rhe epide rmis include the stratum spin oslIm ,a long its length. The primary epiderm a l la minae are kera-whose cells arc undergoing keratinization, and the stratum tinized and fused wi th th e inner portion of the stratu mbasale. The stratu m basale borders on the dermis (corium ), medium of the wa ll. The secondary epidermal lami nae con-wh ich is rich in blood vessels and nerves. The dermis may sist of a core of cells of the stratum spinosum bordered bybe either papillated o r laminated, depe nd ing on whethe rcells of the stratum basa le. The epide rm a l laminae form thethe overlying epidermis con tain s tubular or laminatedstratum inrernum of the wa ll of the hoof. They interdigitatehorn, respectively . The dermis blends wi th underlyingw ith primary and secondary derma l lami nae of the laminarstructures such as the subcutaneous cushions and the pe- dermis. This extensive interdigitation serves to slispend [heriosteum of the third pha lanx.th ird phalanx from the hoof. At the g round surface, the The perioplic epidermis forms a band of soft, nonpig- junction of th e epiderma l laminae of the wa ll (u np ig-mented tubular horn. It merges with the epidermis of the mented) with th e sole is ca lled the wh ite line.skin above and extends downward as a thin, glossy, AakyThe tubu la r and intertubular ho rn of the bulbs, sole,layer of kerati n that forms the o ute r coating o f the wa ll o f and frog is softer than that of th e wall of the hoof. The der-the hoof, ca ll ed rhe stratum tectorium (stratum externum ).mis of these regions, like that of the periople and coronaryThis layer is we ll developed in you ng anim als, but tends to region, is papillated. The epidermis and dermis of the barsbe worn away in o lder horses . The perioplic epidermisare lamina ted, being continuolls with the laminar region ofw idens at the hee ls to form the bul bs. The perioplic dermis the wal l.108 COLOR ATLAS OF VETERINARY HISTOLOGY 117. Periople Epidermal laminaeronary regionSoleWhite line _ __ _ _ Bulb FrogPeriople Coronary region Figure 12.71. Hoof, Horse. The various regions of the hoof are shown. The inner surface of the periople and coronary region and thai of Ihe sale, frog , and bulbs are stippled in Ihe drawing. In Ihe intact toe, dermal papillae extend inlo Ihe funnel shaped depres sions whose openings are representedby the stipples .Sole Frog Laminae of wall_ _ BulbWhite line- Stratum medium, deep unpigmented layer Figure 12.72. Sole, Hoof, Horse.INTEGUMENT 109 118. I 1"9 , ! 2 .Figure 12.73x 12.5 Figure 12.77 x 25 KEY1. Bone, PJ 10. Hair follicle, developing 2. Cartilage, developing P311. Hom tubule 3. Coronary dermis 12. Horn tubule, cortex 4. Coronary epidermis13. Horn tubule, medulla 5. Dermal papilla14. Interi1Jbulor horn 6. Dermis, ~Ie 15. Laminar dermis 7. Dermis, woll16. Perioplic dermis 8. Epidermis, sole 17. Perioplic epidermis5 9. Epidermis, wall-.::i.- Figure 12.73. Developing Hoof, I.s., Fetus, Horse. The regions~,.. .. . that form the three layers of the hoof wall are apparent: the peri. -. .3" oplic, coronary, and laminar regions." . -. ... .Figure 12.74 x 25Figure 12.74. Developing Hoof, Coronary Region, I.s., Fetus, Horse. Portion of coronary epidermis and coronary dermis, later in development than in Figure 12.73, showing tubular and inter- 14tubular horn . The medulla and cortex of the horn tubules are - formed from the cells of the stratum basale that cover the tip and the sides of dermal papillae, respectively. Intertubular horn is formed by cells of the stratum bosole that are located between the bases of the dermal papillae. (Photograph of a histologic section borrowed from the College of Veterinary Medicine, Iowa State University.) -"12 Figure 12.75. Developing Hoof, Coronary Region, I.s., Fetus, 14Horse. Detail of Figure 12.74, showing two horn tubules in longi tudinol section. (Photograph of a histologic section borrowed from the College of Veterinary Medicine, Iowa State University.) Figure 12.76. Hoof, Coronary Reg ion, x.s., Horse. Dermal papillae and horn tubules of tubular horn. (Photograph of a histoFigure 12.75 x 125 logic section borrowed from the College of Veterinary Medicine, Iowa State University.) Figure 12.77. Developing Hoof, Wall and Sole, x.s., Fetus, Horse. The dermis of the wall is laminated, while that of the sale is papillated .Figure 12.76110COL ATlAS OF VETERINARY HISTOLOGYOR 119. KEY I . Basal cell 7. Epidermollamino, 2. Blood ve"elsecondary3. Bone, PJ 8. Horn tubule4. Dermal lamina, primary 9. laminar dermis5. Dermollomino, secondary 10. Stratum medium6. Epidermollamino, primaryFigure 12.78. Developing Hoof, Wall, x.s., Fetus, Horse. Detailof Figure 12.77. The epidermal laminae, ot this time , consist10mainly of a layer of basal cells Istratum basale). Primary epider-mal laminae hove begun to form secondary laminae. The primaryand secondary dermal laminae are extensions of the laminar der-.mls.Figure 12.78 x l25Figure 12.79. Hoof, Laminar Region, x.s., Horse. Horn tubulesof the stratum medium are seen in cross section. Primary and sec-ondary epidermal laminae of the stratum internum interdigitatewith the laminar dermis, which anchors the third phalanx to thewall of the hoof. Epidermal laminae, which are long ridges, ap-pear featherlike in cross section. IPhotograph of a histologic sec-tion borrowed from the College of Veterinary Medicine, IowaState University.)Figure 12.80. Hoof, laminar Region, X.So, Horse. Primary epi-dermal laminae of the stratum internum, continuous with the stratum medium, bear secondary epidermal laminae. These interdigitate with primary and secondary dermal laminae. The secondaryepidermal laminae and the dermal laminae comprise the sensitivelaminae. Nudei of the basal cells appear as small dark spotsalong the periphery of secondary epidermal laminae. Whoto-graph of a histologic section borrowed from the College of Vet-Figure 12.79 x 12.5 erinary Medicine, Iowa State University.)Figure 12.80 x90INTEGUMENT 111 120. I I, .- -- - ,----Figure 12.81 x 25Figure 12.85 x 250KEYL Axial blood ves ..1 10. Feather muscle 2. Borbs, pigmented I L Feather pulp 3. Corneous cells12. Feathersheath 4. Corneous connection13. Horn tubule 5_ Dermal papilla 14. Intertubular hom 6. Dermis 15. Melanocyte 7. Epidermal collar 16. Stack of nuclei 8. Epidermis17. Stratum corneum 9_ Feather follicle 18. Stratum germinativum Figure 12.81. Hoof, Sole, oblique sec~on, Horse. Dermal papil lae and horn tubules of the sale are shown _(Photograph of a his tologic section borrowed from the College of Veterinary Medicine, Iowa State University.)Figure 12.82 x 125 Figure 12.82. Skin, Neck, Chicken. The epidermis of feathered skin is very thin and composed of a stratum germinotivum and stratum corneum. The layers of the stratum germinativum are evi- dent in Figure 12_92_ Nuclei of the epidermal cells are o~en or- ganized into stacks perpendicular to the surface. Abundant small blood vessels appear in the superficial region of the derm is. Figure 12.83. Feather Follicle, Skin, Neck, Chicken. Oblique section through the basal region of a follicle with a developing feether. An e~idermal collar surrounds the dermal pa~illa _ The up per portion of the dermal papilla blends with the teather pulp. Figure 12.84. Skin, Chicken. Oblique sections of developing can tour feethers . Figure 12.85. Skin, Chicken. Oblique section of a developing contour feather . Melanocytes lie among cells of the barb _BarbuleFigure 12.83x 62.5 cells, beginning with the outermost ones, receive pigment fro m the processes of the melanocytes. . ~ ..- :.t _" . -,:;., r. "-:"!i~~.. .-,-. ...."Y.-, . . ..l.-t.......--.:. ,,~. ."-. ~ ~.. ,. ~ . ..... -1.~.1 - . Figure 12.88. Skin, Chicken. Cross section of a contour feather.~ .~ l- oJii......~- l ,-- J .-,v. ....,..... _.. . . . .. & ": .. .I. .~ " "i -~ , , ,c.. ~ ...showing numerous barbs. -- ,, , " ." / ," .. ........ .....; ~ . ". 6" UI~_... ". . .". .. .. , , .....".. .. T-. r.. " ..... .., . ... .~.. . ~ .. ... . . .... ~~ ~L. -..... ..". ,,- .- .., , . .. -- . ..... .. - .I ~. - -- --~~.--_, .,~, , .,." -. ." 31Figure 12.87 x l25- ,-- - ..... ., . , " :/, . - .-, --- .._., .,. .- ., , - .,-.. . .... 5.,.. . , . , ~ 1,2 .. .. ::;-. -- - .--- < -. , . - e-, . . _, ,,- -,!oplasm, form a thick layer in the glycogen zone. The pale cells of the central layer a re less numerous. Compare with Figure 12.110.Figure 12.105Figure 12.106 x 12.5Figure 12.107 x 12.5118COLOR ATLAS OF VETERINARY HISTOLOGY 127. MAMMALShe digesti ve tract extends from the mo uth to the anus. Generall y, its wa ll is CO I11-posed of an outer serosa (or an adventitia ), muscularis externa, submucosa, and in-ner mucosa. The mucosa consists of an in ner epithelium, a middle lamina propria,and an o uter muscularis mucosae. A musculari s mucosae is absent fro m the mo uth, phar-ynx, ponions o f the esophagus, and th e rumen. The mouth lacks a submucosa and mus-cularis externa. From the li ps through the nonglandu lar stomach, the epithelium of the mucosa isstratified squa mous. Among other places the epithelium is keratini zed on the dental pad,surface of rh e tongue, hard pala te, cheek, and the no nglandular sto mac h o f rum inan ts,horses, a nd pigs. The epithelium of the mucosa in the gla ndular stomach and the intestineis si mple columnar; in the anal canal it is st.ratified squamo us. From the mo uth thro ugh th e eso phag us, th e mucosa is moistened by th e secreti ons(mucous o r sero us) o f vario us glands, includin g the majo r sali vary g land s. Surface mu -cous cells and mucous neck cells of the stomac h and go blet cells of the small and large in-test ines also contribute lubricatin g secretio ns.T he tongue has vari o us small o utgrowths, papillae, loca ted primaril y on its uppersurface. These va ry considera bly in size a nd appearance. Some (filiform ) have threadlikeprojections Ot bear spines. Some are cushion-shaped (circumvallate, fungiform ), whileothe ts (foliate ) ta ke the fo rm of a succession of folds. Taste buds occur in the epitheliumof circ umva llate, fol iate, and fungifor m papillae. The oropharynx is lined by a stratified squamous epithelium and contains mucousglands, except in carn ivores, where the glan ds are mixed . A muscularis exrerna of skele-tal muscle is surro unded by an adventitia.Througho ut mOSt of its length, the esophagus is surrounded externall y by an adven-titi a. The muscu laris externa va ries in compos ition. In the dog it is composed of skeletalmuscle throughout its length, except in the vicinity of th e stomach, w here skeletal muscleis replaced by smoo th muscle. In ruminants the entire muscular is externa is comprised o f119 128. skeletal muscle. In the horse and cat a switch from skeletal in carnivores. At the bases of the vi ll i are in vagi nati ons ofto smooth muscle occ urs in the ca udal third of the esop ha-rhe epithelium, rhe crypts of Lieberkiihn (i ntestina l glands).gus, whereas in rhe pig the change occurs just cranial to theReplacement of the mu cosal epirhelium occurs by cell d ivi-diaphtagm. sion primarily w ithin th e crypts. A musc ularis mllcosae,The mu cosa of the eso phagus is li ned by st tatified consisting of two layers of smooth muscle, se parates th esqua mous epitheli um. The longitudinally arranged smoothcrypts from th e underl ying submucosa. The latter is formedmuscle of the esophageal muscularis mucosae var ies in from loose con necti ve tissue in th e horse, rum ina nt, a ndamount from anterior to posterior. It is in the form of iso- pig. In contrast, it is composed of moderately dense con-lated bundles anteriorly and a co ntinuous sheet posteriorly nective tissue in carnivores. A lamina subgla ndul aris mayin the car, horse, and ruminant. In the dog and pig it is ab-be present in the intesti ne of carnivo res. The remainder ofsent anterio rl y and appears as a continuous sheet posteri- t he wall of the intestine is comprised of a muscularis ex-o rl y.tern a of s11100th muscle and a serosa . Mucous o r mixed gla nds occur in the su bmucosa of Co mpo und, tubuloacinar Brunners glands (duod enalth e esophag us. In th e cat, horse, a nd rumi nant, glands oc-glands, submu cosal gla nds) are mucous gla nds occ urri ngcu r only at t he junction o f the pharynx a nd esop hagus. In with in the submucosa a nd o ften w ithi n the la min a pro priathe pig they occur anter iorly, di mi nish in the mid-region,of th e duodenum. In carnivores, sheep, a nd goats they areand are spa rse caudally. In rhe dog rhey occupy rh e entire limited to th e initial or mid-region o f the duodenum; inlength of the esophagus and exte nd into the stomach for a horses, pigs, a nd cows they extend into the jejunum. Brun-shorr distance.ners glands also project into the pyloric sto ma ch for a. The horse, ruminant, and p ig have a no nglandu larshorr distance. Aggregario ns of Iympharic nodules, Peyersforestomach and a gla ndular stomach. In ruminants t hepatches, are present in th e lam ina propria a nd su bmucosafo restomach is d ivisible into a rum en, reticul um, and o ma-of the small intesti ne, especially the ileum.sum. T he glandular sto mach of ruminants is the abo ma- T he mu cosa of the large intestine presents a flat sur-sum. The car and dog have a glandula r stom ac h, bur lack a face. Vill i are absent. Crypts are longer t han in the small in-forestomach. In all of these ani mals the glandular stomachtestine. Flat bands, taeni a coli, consisting of lo ngi tud inall yconsists of cardi ac, fundic, and pyloric gland regions. The a rra nged smooth muscle and elastic fibers, occ ur in thecardiac gland region is re lative ly sma ll in all but the pig.colon of horses and pigs. Similar structures, taeni a ceci, oc- cur in the cecum. T he rectum termi nates at the anal canal,The epithel ium of th e gland ular stomac h invaginates w hich is lined by a stratified sq ua mous epirhelium. T he ep-into t he lamina propria, forming tubula r structures ca lled ithel ium is nonkeratinized in t he anterior portion of thegastric pits (foveolae). Depressions of th e mu cosa kn own as cana l an d kera tinized in t he posterior portion, wh ich isgastri c furrows are also present. continu o us w ith the hai ry skin. T ubu loaci nar anal glandsVarious tubul ar gla nd s empty into th e bottom o f rhe occur in t he submucosa a nd musc ularis of the a na l canal ingastric p its. M ucous gla nds with occasional parietal cells carn ivores and pigs. Circum anal glands occur in th e sub-are the principal type fo und in t he cardiac gland region. In cutis aro und the a nus of the dog. The upper porrio n ofthe fundi c gland region glands are constructed mostly of these g lands is sebaceous, whereas th e lower portion isparietal and chief cells, which secrere hydroch loric acid and nonsebaceous. The cells of the latte r resemble hepatOcytes.pepsi nogen, respect ively. The glands of the pylo ric gland Accordingly, the nonsebaceous region is ofren ca lled a hep-reg ion are mainly of the mu co us type w ith interspersed atoid gland.parietal cells. Paired anal sacs occ ur lateral to an d below th e a nu s of In carnivores the mucosa o f the fundi c gla nd region is carn ivo res. Each is lin ed by a kera tinized, strat ified squa -separated into an adoral, narrow, and thin light zone andmous epithel ium and is loca ted between the inner smoothan abora l, wide, a nd thick dark zo ne. These zones are read- muscle of the internal a nal sphincter and the ollter skeletalily visib le on gross exami nation o f the mucosa a nd are dis-muscle of the external ana l sp hincter. The exc retory duct oftinguishable histologically. The sto mach of the cat has a eac h gland opens into the keratin ized porrion of th e a nalrhick layer of conn ecrive ti ss ue between rhe base of theca na l. Glands of the anal sac are apocrine tubular in theglands and the musc ularis mucosae called the stratum COffi- dog. In rhe ca t borh apocrine rubular glands a nd sebaceouspactum. T his m ay be ca pped by a layer of fibrob lasts, thegla nd s su rround the a nal sac.stratum granulosum. The co mbination of these cells andThe li ver is a large, lobed gland. Eac h lobe is coveredthe stratum com pactum is ca lled th e lamina subgla ndu-by a mesoth elium, beneath w hi c h is a thin connective-laris. The latter may be abse nt in dogs. A submucosa, mus-ti ssue layer, the capsule of G lisson. Each lobe is di videdcu lar is externa of smooth muscle, a nd serosa complete the into numerous classic lobules. These consist of sinusoidswa ll of the sromach . and of plates of pa renchyma cells, hepatocytes, radially or-The intestines o f mammals consist of a small intestinega nized abollt a central vein. Lobules are indisti nctl y se pa-(duode num, jejunum, a nd ileum ) and a large intestine (ce- rated from one a nother in a ll ani mals except the pig, incum, colo n, rectum, a nd anal ca nal) . In both the small a ndw hic h an abun dance of co nn ective tissue between lo buleslarge intesti ne, the epithelium is simple columnar with a stri- clearly iden tifi es rheir boundaries. Portal tracts (a rea s) oc-ated border. Goblet cells occur a mong the columnar cells. cur at th e interstices of three or more lobu les. Each tractT he former increase in number fro m anterior to posterior contains one or more branches of a porta l vei n, hepaticwith the greatest number occ urring in the large intestine.arrery, bi le ductule, and lymp hat ic vessel. These var iousVilli a re confined to t he sm all intestine in mammals. components are supported by a framewo rk of connecti ve They are short a nd dli ck in ruminants but long and slender tissue.120COLOR ATlAS OF VETERINARY HISTOLOGY 129. Bile, secreted by hepatocytes, enters ti ny bile ca naliculi Depressions between the folds are called sulci. T he epithe-from wh ich it flows into the canals of Hering, located closelium is simple columnar except at the base of the sulci,to each portal tract. The cana ls un ite with the bile ductule where it is cuboidal. The wall of the proventriculus consistsof a portal tract. Bile ductules lead into bile ducts. The ep- of large, compound , t ubu lar g la nd s. The secretory cells,ithel ium of bile ductules is simple cuboidal, w hereas that ofwhich are cuboidal to low coiUInnar, produce both pepsino-the bile d ucts is simple columnar. Goblet ceUs occ ur in thegen and hydrochloric acid, t hus combining the functio n ofla rgesr bile ducts. mamma lian chief and parietal cells. Each gla nd ope ns to the The gallbladder is a storage depot for bile. Its mucosa islumen of th e sto mach through a conical papilla.thrown into numerous folds when the bladder is contracted. The ventriculus is a highly muscular gri nding organ . ItWhen it is d istended, they mostly d isappear. The sim ple is lined by an epitheli um tha t invaginates into the laminacolumnar epithel ial lin ing has a striated borde r. Goblet cellspropria, formi ng elongated pits, each of which bears termi-have been reported in rhe epithel ium of the cow. We havena l tu bular gastr ic glands. Cells of the latter secrete a t hick,also observed them in the goat. Mucous, serous, or mixed horn y material. Although keratin-like, this substance, usu-glands are often seen in t he wall of th e ga ll bladder of rumi-all y called keratino id, is not chemically eq uivalent to ker-nants. The smooth muscle of the muscularis is arranged cir-atin. It forms the tough inner lining, about 1 mm thick, ofcularly (mostly oblique, accordi ng to so me) for the most the ventricu lus.part. T he ga ll bladder is absent in the horse. The intestine of the chic ken is si milar in structure The pancreas consists of numerous ru buloacinar secre-throughout its length . It consists of a duodenum, jejunum,tory un its, w hich for m the exocrine component of the or-ileum, and large intestin e. A pair of blind, elongated cecagan. Clusters of epi t helial cells, t he endoc rine islets of join the intestine at the junction of the ileum and large in-Langerhans, are scattered among the secretory units. Tubu- test ine. The termi na l end of the large intestine joins the co-loacinar units drai n into long, narrow interca lated ducts, p rodeum o f t he cloaca. Vi lli are present throughout t hewhich are lined by elongated cells t hat present a cuboidalsmall and large intestines. They are longest in t he d uode-appearance w hen sectioned transversely. Interca lated ducts num, bu t gradua ll y shorten and t hic ken caudally. In the co-communicate directl y with in terlobular ducts. Striated (se-prodeum they are stumpy and wunded. Villi are present incretory) ducts are not present. Unlike sa livary glands, my- the ceca also, becoming fl attened toward t he blind end.oepithel ial cells are lacking aro und the secretory units.C rypts of Lieberkiihn a re short an d open between the villi,Pacini an corpuscles are commonly fo und within the con- as in mam mals. Although the wa ll of the intesti ne of thenective tissue of the pancreas of dogs and cats. ch icken is simi lar to that of the mamma l, rhe absence of duodenal glands and an extremely thin submucosa in the ch icke n are notable d ifferences.CHICKENAs in ma mmals, the liver is covered by a mesothe