Notes on Veterinary Anatomy

Chapter Viii. Embryology or Development of the Foetus 81

PREFACE

There are a number of excellent works on Veterinary Anatomy, and many of them will amply repay the student for the time taken to master them, but for quick reference none seem to contain the wants of the veterinary practitioner and student for which this humble little work is primarily intended.

It has been my endeavor to briefly describe each organ as found in the healthy animal; its functions, etc., in a condensed yet complete form. I am positive that the student or veterinary practitioner will find its pages highly instructive as well as profitable and interesting.

In compiling this work a few authorities have been consulted and quoted, while it has not been practical to give individual credit for the use of ideas and language, a general acknowledgement is here made:

Veterinary Science, Hodgins and Haskett.

Veterinary Anatomy, Strangeways.

CHARLES J. KORINEK, V. S.

DESCRIPTIVE ANATOMY

Osteology is a term applied to that section of descriptive anatomy which treats of the bones. Arthrology, to the consideration of the joints or modes of union between the bones, while by Myology is meant the doctrine of the muscular system. Splanchnology treats of the viscera, Angiology of the circulatory and absorbent systems. Neurology deals with the nervous system. Aesthesiology with the organs of sense; while Embryology, as before stated is the consideration of the animal frame at periods preceding its birth.

In this work the various departments are discussed in the order here given. The structures which are the subject of the first three divisions are sometimes classed together as the Organs of Locomotion; for bones form the frame work of the body and often act as levers; the joints connect the bones, permitting more or less motion between them; while the muscles move the bones, and so produce motion of a part of the body--or it may be locomotion, or change of situation in the entire frame.

In the study of comparative Anatomy the terms analogy and homology are frequently met with. Although these words are unfrequently used indiscriminately, the following differences should be noted. Organs are said to be analogous when, though differing in structure, they perform the same function; but when their functions are different, which, in the broad sense, they correspond in structure or form, they are said to be homologous. Thus the middle finger of the human hand is the homologue of the anterior (front) digit of a horse, because they have the same general structure, and relation to the rest of the limb; but as the functions they perform are quite dissimilar, they cannot be termed analogous. Again, the lungs of a mammal are analogous to the gills of a fish, for, though they differ widely in structure, position and form, and are therefore not homologous, their ultimate use is the same--each of them being an apparatus in which is carried on the process of purifying the blood.

DISSECTION.

Students must dissect as many animals as possible, so as to familiarize themselves with the frame work or structure, and the location of the digestive, nervous and blood systems, as it will aid materially in the art or process of determining the nature of various diseases.

During cool weather an animal for dissecting purposes can be kept for a considerable length of time without preservatives

It is well to have a copy of Anatomy at hand when dissecting for it will show the location of the various organs and explain their functions.

SKELETON OF HORSE--AFTER MEGNIN.]

EXPLANATION OF PLATE I

SKELETON OF THE HORSE

1. Skull, or skeleton of the head. 2. Cervical vertebræ or neck bones. 3. Dorsal vertebræ or back bones. 4. Lumbar vertebræ or loin bones. 5. Sacral vertebræ or rump bones. 6. Coccygeal vertebræ or tail bones. 7. Pelvic or hip bones. 8. Sternum or breast bone. 9. Ribs. 10. Scapula or shoulder blade. 11. Humerus or shoulder bone. 12. Radius or bone of the fore-arm. 13. Ulna or bone of the fore-arm. 14. Carpus or bones of the knee. 15. Os Melacarpi Magnus, metacarpal, or cannon bone. 16. Ossa Melacarpi Parva, or splint bones. 17. Proximal Phalanx, os suffraginis, or large pastern bone. 18. Great Sesamoid Bones. 19. Medium Phalanx, os coronæ, or small pastern bone. 20. Distal Phalanx, os pedis, or coffin bone. 21. Os Naviculare, small sesamoid, or shuttle bone. (This bone can be plainly seen Plate VII). 22. Femur, or thigh bone. 23. Patella, or stifle bone. 24. Tibia, or leg bone. 25. Fibula. (This bone is little developed in the horse.) 26. Tarsus or hock bones. 27. Metatarsus, or os metatarsi magnus. 28. Ossa Metatarsi Parva, or splint bones of the hind leg.

Names of joints placed according to numbers.

I. Shoulder Joint. II. Elbow Joint. III. Carpus or knee joint. IV. Fetlock Joint. V. Pastern Joint. VI. Coffin Joint. VII. Hip Joint. VIII. Stifle Joint. IX. Tarsus or hock joint.

CHAPTER I.. Osteology.

OSTEOLOGY.

STRUCTURE OF THE BONES--Bones are hard, yellow-white, insensitive objects, which form the skeleton and give attachment to soft structures (muscles, tendons and ligaments); they are of various sizes, forms and densities. In the limbs the bones are ordinarily more or less long, circular bodies, with expanded ends, effectually supporting the body, supplying leverage and attachment for soft structures, and forming the basis of all joints. Where cavities, such as the cranium, chest, and pelvic, enclosing the organs requiring protection and support, the bones tend to assume a flat, expanded form.

Living bone is bluish pink, insensitive, and elastic; on exposure to air it becomes diseased and blackened, very sensitive and painful; (the teeth excepted) which are harder and of a higher specific gravity than any other bone formation.

Bones are composed of two kinds of substance--animal, which makes the bone tough and flexible; earthy, which makes it hard and fragile. In young animals the animal matter forms about one-half of the bone substance; in the adult, it diminishes to about a third, while in old animals it is still less; hence the bones of very old animals are brittle, more liable to fracture and harder to mend.

Bones in a six-year-old horse contained, Phosphate of Lime, 54.37 per cent; Carbonate of Lime, 12.00 per cent; Phosphate of Magnesia, 1.83 per cent; Soluble Salts, 0.70 per cent, or mineral matter, 68.90 per cent. While they contain Cartilage, 27.99 per cent; Fat, etc., 3.11 per cent, or animal matter 31.10 per cent.

In bone tissue there are two modifications of texture, the compact and the cancellated. The former--hard, dense, and ivory-like, is always situated externally; the latter porous and spongy lies within.

Although the compact tissue appears uniformly dense, and destitute of porosity, yet, if we transversely sectate the shaft of a long bone, and examine it under the microscope, by transmitted light, it is found to contain numerous round openings. These are called Haversian canals. They transmit bloodvessels, and run in a longitudinal or slightly oblique direction, opening on either the outer or inner surface of the bone.

The external (outer) surface of every bone is covered by a tough, fibrous, inelastic membrane called periosteum, which can be seen by examining the bone of an animal which has recently died. The only exception to this is at the joints where one bone articulates with another, and where a tendon or muscle plays over a bone; here we find its place taken by articular cartilage. By its strength it sometimes retains bones in contact after an oblique fracture; in the young, it is thicker and more vascular than in the adult. Blood-vessels which penetrate the periosteum pass directly to the bone; the outer surface of the bone is always studded with numerous foramina through which these enter.

The periosteum owing to its inelasticity, is, when inflamed, the seat of intense pain; and should any part of it be stripped off, there is every probability of the denuded bone dying and separating.

CONTENTS OF BONE.--Red marrow is found in the extremities or near the ends of bones, white marrow is found in the shaft.

CLASSES OF BONES.--Bones are classed as long, flat, and irregular. Long or cylindrical bones are found in the limbs or extremities, and serve as levers and pillars for traveling and to support the body. Descriptively, a long bone is divisible into a center or shaft and two ends or extremities. Flat bones are found where visceral organs need protection. As the shoulder or scapula and ribs, to protect the heart and lungs; pelvic or hip bones, to protect the rectum and urinary and genital organs; also the cranial bones, to protect the vital organ called the brain. Irregular bones are found in the spinal column and in the joints, such as the knee or carpus, hock or tarsus, where great strength is required. They usually possess many angles and indentations, with surfaces for articulation and tendonous attachment, and consist of a thin, dense, external (outer) case of compact bone enclosing cancellated tissue. In proportion to their size they present a much larger extent of articular surface and greater mechanical strength than any other class.

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