1. Only the gross structure is discussed here. For the microscopic structure reference is to be made to histological works.

2. Only a brief general statement of osteogenesis can be made here; details must be sought in embryological literature.

3. As might be expected from the history of anatomy, a good many of these terms are more or less interchangeable; furthermore, a given skeletal feature may differ greatly in various species.

4. The term is employed here, as is usual in descriptive anatomy, to designate only the bony part of the rib (Os costale); morphologically it includes the cartilaginous part also.

5. The manubrium sterni of man is equivalent, strictly speaking, to the cariniform cartilage + the first osseous segment of the horse.

6. The long axis of the skull is considered to be horizontal in these descriptions.

7. The occipital crest of this description is equivalent to the external occipital protuberance and superior nuchal line of man. A curved line a little lower down, which is continued on the paramastoid process, represents the inferior nuchal line of man.

8. Other terms for these parts are basioccipital (basilar part), exoccipitals (lateral parts), and supraoccipital (squamous part). It should be noted, however, that the lines between the basioccipital and exoccipitals pass through the lower part of the condyles.

9. This foramen might well be called a canal, since it is an inch or more in length.

10. The cavity so formed may be termed the sphenopalatine sinus. The sphenoidal sinus may be a separate cavity which communicates only with the ventral ethmoidal meatuses; this arrangement exists in about a third of the cases, according to Paulli.

11. This is also called the subsphenoidal canal or pterygoid foramen.

12. On account of its deep situation, and the fact that it cannot be separated from its surroundings, the ethmoid must be studied by means of appropriate sagittal and transverse sections of the skull.

13. According to Martin, there are originally four centers, two anterior and two posterior (smaller) ones, which fuse in a variable manner.

14. This is commonly termed the styloid process. It is not the homologue of the styloid process of man.

15. This foramen is somewhat variable in position, but is commonly opposite the corner incisor. Smaller inconstant foramina are often present.

16. The alveolus for the temporary canine is commonly formed in the maxilla alone.

17. This bone is really a greatly developed first ethmoturbinal.

18. In the Stuttgart Nomenclator Anatomicus (S. N. A.) the body (Corpus) is the part which bears the teeth, and is divided into a pars incisiva and a pars molaris. The ramus is the rest of the bone.

19. These correspond to the great cornua of man.

20. This relation varies with age; in the young horse the third tooth, in the old subject the fourth, lies below the end of the crest.

21. This bone is probably equivalent to the fourth and fifth carpals of forms in which five carpal elements are present in the lower row.

22. It is also called the large pastern bone or os suffraginis.

23. This bone is also called the small pastern bone or os coronæ.

24. This bone is also called the os pedis or coffin bone.

25. The upper and lower divisions of the wing are sometimes termed the basilar and retrossal processes respectively.

26. This is termed the lacrimal sinus by some authors. It is similar in location and in the position of its orifice to the turbinal part of the frontal sinus of the horse, with the important difference that it does not communicate with the frontal sinuses in the ox.

27. This third bone was termed the phacoid in the cat by Strauss-Durckeim, and is regarded by some authors as the vestige of an additional digit, the prepollex.

28. It is doubtful whether the synovia is a true secretion or a transudate containing products of friction. The view given above is that which is more commonly accepted.

29. This classification makes no claims to scientific accuracy, but is simply a statement of the terms in general use. A grouping based on mechanical principles seems desirable, but appears to be almost impossible on account of the great variety and irregularity of form of the articular surfaces.

30. The movements in some of these joints are more extensive and varied than in some diarthroses. To illustrate this we may compare the movements of the cervical or coccygeal vertebræ with those possible in the carpo-metacarpal or the sacro-iliac joints.

31. In dissecting-room subjects these bursæ and the adjacent structures are commonly the seat of pathological changes. They appear to be the starting-point of “poll evil” and “fistulous withers.”

32. No natural line of demarcation exists between the ligamentum nuchæ and the lumbo-dorsal continuation of the supraspinous ligament, since the change from the purely elastic to the white fibrous structure is gradual.

33. The term is a very unfortunate one, since it is a distinct misapplication of the name as it is used in regard to man. It is, however, very firmly established, and appears likely to persist indefinitely in the absence of a convenient popular equivalent.

34. This is often called the Y-shaped ligament—a rather undesirable name, since it is not bifurcate.

35. It is also called the V-shaped ligament.

36. This should be noted in regard to resection of the lateral cartilage or other operations in this vicinity.

37. These are termed the postero-lateral ligaments by M’Fadyean. They may well be called, as by German authors, the suspensory ligaments of the navicular bone.

38. In this figure the patella is pushed up above the trochlea—a position which it does not occupy normally.

39. This section consists necessarily only of a brief statement of the most important differences in the joints of the other animals.

40. These movements are best seen in man, in whom the back of the hand may be turned forward (pronation) or backward (supination).

41. The student will note in dissection that transition forms occur; also that the same sheath may belong to two or more tendons in common, e. g., the sheath of the two flexors on the back of the carpus. In such cases the synovial membrane is reflected from one tendon to the other, and may form a secondary mesotendon.

42. This muscle is probably the homologue of the sternal portion of the sterno-cleido-mastoid of man. On account of the differences in its insertion in the various animals, it seems desirable to adopt the name sterno-cephalicus.

43. The upper part of this maybe separated from the scalenus proper, and is then termed the cervicalis ascendens or ilio-costalis cervicis—a continuation in the neck of the transversalis costarum.

44. This seems due to pressure produced by pathological changes in the supra-atloid bursa, which are frequently extensive in dissecting-room subjects.

45. The lumbar part of this muscle is subject to variation. It may, in quite exceptional cases, extend as far as the ilium.

46. The muscle as here described includes the spinalis and semispinalis components, as the separation of these is largely artificial in the horse.

47. The function of the intercostal muscles is still a subject of much discussion. The statements made above seem to represent the view most commonly held in regard to their action.

48. It should be noted, however, that in the embryo the diaphragm appears as a paired structure, extending from the lateral walls of the cœlom to fuse with the septum transversum.

49. In order to get a clear idea of the relative positions of these foramina and of the form of the diaphragm, the thoracic surface of the latter should be examined while the abdominal viscera remain in situ.

50. It is narrow and slit-like in the natural condition, but may appear oval in the dissecting-room, especially if the hind limb is drawn back and abducted.

51. It must be admitted that the term “ring” is rather misleading as applied to the abdominal opening of the canal, since normally it is a mere dilatable slit. The ring-like constriction which exists here in the male is constituted by the peritoneum, which descends into the canal to form the tunica vaginalis. This peritoneal ring is termed the vaginal ring (Annulus vaginalis), and must not be confused with the subperitoneal ring, i. e., the internal inguinal ring.

52. As might be expected, the cremaster usually undergoes more or less atrophy, and is paler in the castrated subject. In the mare the muscle is small, and ends in the connective tissue in the lower part of the inguinal canal.

53. The term canal is somewhat misleading; it is rather a slit-like passage or space between the two oblique muscles, since the inguinal ligament is that part of the aponeurosis of the external oblique muscle which stretches between the external angle of the ilium and the prepubic tendon.

54. The obliquity of the tendon and the angle which it forms with the pelvic floor are of clinical importance in regard to manipulation of the fœtus in obstetrical cases. The slope varies in different subjects. In some cases the tendon forms about a right angle with the pubic bones.

55. The terms dorsal and ventral are here used in the topographic and not in the morphological sense. All the muscles of the group are ventral in the latter sense.

56. This is regarded as a vestige of the clavicle. On this basis the portion of the muscle from the vestige to the arm represents the clavicular part of the deltoid of man.

57. Günther states that this muscle assists in extension or flexion according to the position of the head of the humerus relative to the glenoid cavity.

58. M’Fadyean and Vaughan term this muscle the scapulo-ulnaris, while Arloing and Lesbre term it “Ancone accessoire du grand dorsal.” The above name seems to agree best with the chief insertion and action, although it certainly arises largely from the tendon of insertion of the latissimus dorsi.

59. This is considered to represent the part of the common extensor for the fourth and fifth digits.

60. Martin considers that this muscle represents the extensor indicis proprius and the part of the common extensor for the second digit.

61. In man the muscle is an extensor of the hand.

62. On account of the intimate union between the psoas major and iliacus they are frequently considered a single muscle, to which the name ilio-psoas is applied; some anatomists include the psoas minor also under this term.

63. By some anatomists the portion inserted into the crest is termed the gluteus accessorius, but Lesbre considers this the deep gluteus, homologous with the gluteus minimus of man. The portion inserted into the trochanteric ridge apparently represents the piriformis of man.

64. Apparently the muscle represents the biceps, together with part of the gluteus superficialis of man. Hence the names gluteo-biceps and paramero-biceps have been suggested.

65. This muscle was incorrectly designated the adductor magnus by Percivall and Strangeways. Its name, however, is not at all descriptive of its structure in the domesticated animals.

66. It has been customary to describe two adductors—a parvus or brevis, and a longus or magnus. This division is largely artificial, and has been abandoned in the new nomenclature—a return to the views of Bourgelat and Girard.

67. This has been termed by various authors the adductor parvus or brevis.

68. Termed by various authors the adductor magnus or longus.

69. The iliac head is described by some authors as a separate muscle, and termed the pyriformis. This does not seem desirable, especially since it is at least probable that the homologue of the pyriformis of man is that portion of the middle gluteus which is inserted into the back of the trochanteric ridge.

70. The name is based on the arrangement in man, in whom the muscle consists of two fasciculi forming a groove between them for the tendon of the obturator internus. In the horse it is undivided, and is grooved for the obturator tendon, so that at first sight it appears to be double. The gemellus may be regarded as the extrapelvic head of the obturator internus (Gegenbaur).

71. While it is true that the separation of the intermedius is probably never entirely a natural one in the horse, it varies in individual cases, and is usually clear on cross-sections. In some subjects it is possible to separate another slip which may represent the articularis genu of man.

72. It seems inadvisable to retain the old nomenclature, since it is inapplicable to other domesticated animals in which the muscle is well developed (e. g., ox, pig).

73. The soleus may, therefore, be included with the two heads of the gastrocnemius under the name triceps suræ.

74. The origins of these heads are given in the order in which they may be most conveniently dissected, not in order of size and importance.

75. This is probably the homologue of the subclavius of man.

76. Movements of individual digits are specified with regard to the axis of the manus (hand, paw), and not to the median plane of the body.

77. The term “mouth” is commonly used to signify either the oral cavity (Cavum oris) or the entrance to it (Rima oris).

78. The epiglottis may be either in front of or behind the soft palate; most often it is prevelar.

79. In the undisturbed state of the parts there is no space between the tongue and the rami of the lower jaw; consequently the tongue must be drawn aside to see the sublingual crest.

80. It will be noted that this definition of crown and root does not agree exactly with the popular view that the crown is the free portion and the root the embedded portion. The objection to the latter statement lies in the fact that it is not capable of general application. Thus the morphological crown of the permanent molars in the horse is extremely long, and is, for the most part, embedded in the bone in the young animal. The root proper begins to form at four or five years of age, and continues its growth for about eight years. As the exposed part of the crown wears down, the embedded part pushes out of the alveolus, thus preventing deficiency of length. On the old basis we should have to say that successive portions of the root become crown, while in point of fact it is only in very extreme age that the true root comes into wear.

81. Ellenberger found, as the result of extensive observations (8000 subjects), that about 2 to 3 per cent. of mares have erupted canines in both jaws; that 6 to 7 per cent. have them in the upper jaw; while 20 to 30 per cent. have them in the lower jaw.

82. It is interesting to notice that vestigial canines are not at all uncommon in mares, especially in the lower jaw. They are very small, and do not usually erupt; their presence is indicated in the latter case by a prominence of the gum. This is in conformity with the fact that they were present in both sexes in Eocene and Miocene ancestors of existing equidæ.

83. It is common in veterinary works to call all the cheek teeth molars, since, in the horse particularly, the premolars are molariform, i. e., do not differ materially from the true molars in size or form. The term cheek teeth conveniently includes the premolars and molars.

84. The student is advised to amplify these very general statements by the examination of heads of subjects of varying ages. It may also be noted that the position of the septum between the two divisions of the sinus varies much.

85. Careful observations (especially on frozen subjects and those in which the organs have been hardened in situ) show that there is no abdominal part of the œsophagus in the strict sense of the term. The stomach here lies directly on the diaphragm, so that the last inch or so of the œsophagus is placed obliquely in the hiatus œsophageus, and is partly covered by the pleura, but not by peritoneum. In soft subjects the weight of the stomach, or traction on it, draws part of the œsophagus into the abdomen, inclosed in a collar of peritoneum.

86. The potential lumen is difficult to determine at all accurately. When distended, its diameter (according to Rubeli) varies from 5.7 cm. at its origin to 4 cm. at its cardiac end. The thickness of the wall varies (inversely as the lumen) from 4 mm. to 1.2 cm. or more.

87. At the origin of the tube muscular bundles arise on the raphé pharyngis and blend with the crico-pharyngeus. Ventrally fibers come from the depression between the cricoid and arytenoid cartilages. Bundles of striped fibers may be continued in the superficial part of the muscular coat as far as the cardia.

88. This method of division, although long in use, is of very little value for accurate description. It is mentioned here chiefly because agreement on a more useful topographic method has not been arrived at.

89. Only a general account of the arrangement of the peritoneum is given in this section, since a detailed description cannot be understood without a knowledge of the viscera concerned.

90. This is the position in the expiratory phase as usually seen in the dead subject. In inspiration the saccus cæcus lies under the upper parts of the sixteenth and seventeenth ribs.

91. This occlusion is usually so complete that distention of the stomach by air or fluid forced in through the pylorus may be carried far enough to rupture the stomach without ligating the œsophagus.

92. No natural line of demarcation exists, but there is a marked increase of the thickness of the wall toward the terminal part. Other differences will be noted in the further description.

93. It will be noticed that the mesoduodenum is not continuous with the great mesentery, but ends by a free edge. The mesentery begins on the opposite surface of the end of the duodenum, so that the bowel is attached by two peritoneal folds at this point.

94. Abnormal displacement, e. g., torsion of the left parts, is not rare, and is liable to produce death if not promptly reduced.

95. There is no natural line of demarcation between the small colon and rectum: the plane of the pelvic inlet is selected for convenience of description.

96. The anterior part of the rectum is very variable in position and relations. It is not often median, but may be deflected either to right or left. Most often it is pushed to the left by the pelvic flexure of the colon. In other cases—especially when empty—it may lie against the right wall, and the space to the left is occupied by the small colon. The amount covered by peritoneum dorsally and laterally is very variable, and appears to be in inverse proportion to the fullness of the bowel.

97. A descriptive method based on that in use in human anatomy cannot be applied with clearness to the organ in the horse.

98. These impressions are not evident on the soft organ. In hardened material they are clearly mapped out, although of course variable in size, in conformity with the degree of fullness of the various hollow viscera. The cæcal impression may not be evident if, as often happens in old horses, the right lobe of the liver is much atrophied.

99. Flower and Ruge describe the mammalian liver as being primarily divided by the umbilical fissure into two parts, the right and left lobes. Secondary fissures on either side may subdivide each of these primary lobes. On this basis we may recognize in the liver of the horse right lateral, right central, left central, and left lateral lobes. In the young foal these four lobes are distinctly recognizable. The two central lobes would correspond to the middle lobe of the foregoing description, and the right central lobe would be the equivalent of the quadrate lobe of man.

100. In the young foal the interlobular tissue is more abundant and the lobulation correspondingly distinct.

101. The hepatic veins may be recognized on section from the fact that they remain open, being connected closely with the parenchyma.

102. The ductless glands are organs which elaborate substances which pass directly into the veins or lymphatics, instead of being conveyed away by ducts. This process is termed internal secretion. The ductless glands include the lymph glands, which are described with the organs of circulation; the thyroid and thymus bodies, described usually with the respiratory organs; the adrenal or suprarenal bodies, described with the urinary organs; the pineal and pituitary bodies, described with the brain; and the spleen, described with the digestive system as a matter of convenience. The spleen is not, strictly speaking, a gland at all: it is not epithelial in origin or structure, but is mesenchymatous.

103. The student is strongly recommended to study the peritoneum of a foal or other small subject when the opportunity occurs, as in these the viscera are easily handled, and the course of the peritoneum can be followed without difficulty.

104. The passage is subject to a good deal of variation in caliber and is sometimes completely occluded.

105. In dissecting-room subjects (which are usually aged) the omentum often exhibits pathological changes, such as adhesions, rents, tumors, formation of twisted strands, etc.

106. The student will note here the difference between the structure and behavior of the brachydont (short-crowned) incisors of the ox and the hypsodont (long-crowned) type of the horse.

107. In popular language these are conveniently regarded as so many stomachs, and termed accordingly “first,” “second,” etc. Other names are in common use, e. g., paunch, honeycomb, manifold or manyplies, and rennet or true stomach.

108. It has been customary to term the sacs left and right respectively, but these do not represent the relations as they exist in situ and as they are presented on frozen sections.

109. It is important to notice that the reticulum is separated from the pericardium by an interval of about 1 to 1½ inches (ca. 2 to 4 cm.) only, since foreign bodies which are often swallowed by cattle lodge in the reticulum, and not rarely (if sharp) perforate the reticulum and diaphragm.

110. The epiglottis in the pig seems to be constantly retrovelar. The pig frequently breathes through the mouth, and this is no doubt possible only when the soft palate is raised; it seems probable that it is also shortened.

111. The canines of the pig are “permanent pulp” teeth and therefore capable of continued growth, and are without roots in the strict sense.

112. It is usually stated that the cardiac end is funnel-shaped, but it is not so in formalin-hardened cadavers nor in frozen sections. The hiatus œsophagus is a long slit in the right crus of the diaphragm, and the terminal part of the œsophagus, which lies in it, is flattened transversely.

113. It will be noted that the fundus gland region does not extend up to the lesser curvature; here the cardiac mucosa joins the pyloric.

114. The description here given is based mainly on the appearance of the organ as hardened in situ, which differs radically from that of the soft organ, as is seen on comparison of the annexed figure (Fig. 321).

115. In the bulldog, which is very prognathic (“undershot”), the lower canines are opposite to or slightly in front of the plane of the upper incisors, and the upper canines are about opposite to the first lower cheek teeth. In the epignathic (“overshot”) dachshund the lower canines are under or slightly behind the upper ones.

116. Increase in number also occurs, the supernumerary teeth being at either end of the series.

117. The valve does not seem to be efficient, since experience shows that rectal injections can be made to pass beyond it. This may be partly due also to the fact that the terminal part of the ileum runs horizontally forward, and the ileo-cæcal orifice faces into the beginning of the colon.

118. Ellenberger and Baum state that the cæcum may reach a length of 20 cm. in very large dogs.

119. When the stomach is very full, it pushes the left portion of the colon over to the right, producing an acute angle in place of a transverse branch. The terminal part of the colon is thus oblique in direction.

120. An external nose (Nasus externus), such as exists in man, forming a projection distinctly marked off from the rest of the face, does not exist in the domesticated animals.

121. The septal cartilage is to be regarded as an unossified part of the mesethmoid. It will be noted that the line of demarcation between the bone and the cartilage is irregular and varies with age; extensive ossification for calcification) of the cartilage is commonly found in old animals. The process often results in the formation of calcareous islands in the cartilage.

122. In the ordinary position of the head and neck, and while the parts are at rest, about half of the larynx lies between the branches of the mandible; when the head and neck are extended, proportionately more of the larynx lies behind a plane through the posterior borders of the rami. It is here described in the position it occupies when the head and neck are extended.

123. The term glottis is commonly used to designate the interval between the vocal bands and arytenoid cartilages or the structures that inclose that space.

124. In so-called œdema glottidis this loose submucous tissue becomes infiltrated with fluid, in some cases causing occlusion of the vestibule.

125. The arrangement of the muscles should be noted, since the space inclosed by the divergence of the sterno-cephalici and the convergence of the omo-hyoidei is the area of election for the operation of tracheotomy.