Anatomy of the Horse. Name, &c. Origin and Insertion. Use. Inner obturator. 1, 2, 3, fig. From the edge of the thyroid hole, into the To assist the gemini. 12. Pyriform. Popliteus. 28, 29, fig. 11. Tibialis anticus. 14. Gastrocnemius. Plantar. 40, fig. 9. Perforated flexor of the foot. Larger perforating flexor of the foot. Lesser perforating flexor of the foot. The long extensor of the foot. Lateral extensor of the foot. Lesser extensor. thigh with the preceding. From the sacrum within the pelvis, inserted as From the external condyle of the thigh bone, From the fore part of the external condyle of the thigh-bone, into both canons by two por- Ditto. To draw the leg inwards. To bend the leg strongly. From each condyle of the thigh-bone, into the To extend the canon. From the upper part of the spine of the tibia, inserted as the former. The four figures to which we have referred also represent the following parts. Vena saphæna; 21, fig. 9. Capsular ligament of the knee; 3, 4, fig. 10. Sciatic artery; 34, fig. II. Gluteal artery; 35, 35, fig. 11, Crural vein; 38, fig. 11. Popliteal artery; 39, 52, fig. 11. vein; 53, fig. 11. Crural nerve; 35, fig. 12. CHAP. II. Of the Stomach and Bowels. Anatomy of the Ilorse. 104 In the horse there is but one stomach, which is very Structure small in proportion to his general bulk; and is partly of the membranous, partly cuticular, and partly muscular. stomach It is situated immediately behind the diaphragm, in the left hypochondrium, and in part of the epigastrium, with its expellent orifice extending across the spine to the right, which is the reason that lying on that side is judged more wholesome than sleeping on the left. It has two surfaces, which may be called its sides, though one is posterior, and the other anterior; and two extremities, a large and a small; the superior surface of which receives the gullet, and is called its cardiac orifice; while the former ends in the duodenum, and is termed the pyloric orifice; this extremity, when the stomach is distended, is the most posterior of the two. The hollow part situated superiorly, only forms its lesser curvature, as the lower portion forms its great curvature. Thus when the stomach is moderately distended, it lies in an obliquely transverse direction, with its great extremity a little forwards, and its two orifices superi Anatomy or, but the cardiac the most so, with the lesser extreof the mity rather posterior to the other, and the great curvaHorse. ture inferior. It is evident that the situation of the stomach must vary much with its distension: the foregoing description answers to it when moderately distended only; but where it is very much filled, the left extremity will press upon the diaphragm, and the right will be carried more posteriorly. In oxen and sheep, where the first stomach is large, it is found, when distended, to have its left extremity carried quite into the left iliac region; in which part it is usually punctured, when they are hoved: but such an idea of the stomach of the horse would prove very erroneous; for this animal has a very small one, and therefore its situ*Blaine's ation can never be such *. Outlines, vol. ii. From a distended stomach pressing upon the diaphragm, we are at no loss to understand, why breathing is impeded after a full meal, when a horse appears to labour for breath; for he is forced to use the intercostal muscles, and the muscles of the shoulder and fore extremities, to open the chest, the posterior enlargement being prevented from the diaphragm being fixed by the pressure of the stomach; hence we see the great impropriety of galloping horses after watering, to warm it in their bellies, as it is foolishly termed. Horses, when grazing, if they drink, are never observed to do this; if it was necessary, nature would dictate it to them. How hurtful it is likewise to ride bard, after a horse has been fully fed, is equally evinced. The stomach has externally a covering from the peritoneum, which adheres closely to it, by means of its cellular portion; and which portion is dipping in between the muscular fibres. Its middle portion is made up of muscular fibres, which are more numerous in this animal, than in the ruminant; making this kind of stomach a medium between the membranous one of some animals, and the true muscular stomach of others. The direction of these fibres is various; but they may principally be referred to a longitudinal and a transverse order, though neither of them are regularly so, and are intermixed with others, whose direction is very oblique, and interlaced with each other. The longitudinal plane is the most external of the two, and appears a continuation of the external plane of the esophagus, with some original fibres, which spread over the lesser curvature, being carried obliquely round, and likewise over the great extremity, forming themselves into a kind of vortex, whose centre is in the middle of that extremity. The inner plane is by much the larger, and is not quite circular, but slightly oblique, crossing the obliquity of the longitudinal plane. This circular plane is very thick and strong round the cardia, or that extremity into which the oesophagus terminates. They are here so very thick as to form a true sphincReasons for ter; and to this it is in some measure owing, that a horse cannot vomit; for when the circular and longitudinal fibres are acting from the pylorus to the cardia, by any irritation that reverses the usual motion, producing an effort to vomit, the circular and longitudinal fibres of the cardia being infinitely stronger and more numerous, are contracting this orifice (especially the citcular), as the others are contracting the other parts; for as the muscular fibres exist equally throughout the stomach, by which the motions are effected, it cannot be simply from the existence of the circular covering to VOL. VIII. Part II. 105 the horse's not vomit. ing. + the first portion of his stomach, that he cannot vomit; Anatomy for it is reasonable to suppose the fibres act throughout of the the stomach by the common consent of parts; nor do Horse they of actual necessity want an immediate stimulus to their surfaces; for were this the case, the fibres of the oesophagus would not by the presence of the masticated bolus be stimulated to contract through the cuticular coat, which equally here lies over the fibres; nevertheless, the cuticular coat of the stomach is probably assisting in this difficulty to regurgitate: it does it by lessening the liability to nausea, which seldom takes place in the horse; and as vomiting is only an effort to remove nausea or its cause, so nature not having given the disease, has not provided the means for its removal. As likewise vomiting appears to be a reversing of the peristaltic motion of the stomach; which motion, in its natural state, begins from the cardia, and ends at the pylorus; so in this reversed state, it commences at the pylorus, and ends at the cardia, thus regurgitating its contents; so it is very probable that the cuticular covering may lessen this inverted peristaltic motion in the upper portion, though it cannot wholly destroy it; and hence cannot be the only, or the principal reason of the impossibility, or rather of the difficulty with which this animal vomits; for instances have occurred where it has taken place. A horse in Sussex was seen to regurgitate a large quantity of grains, and we have heard of one or two other instances; but these must be regarded as very rare occurrences. It is not, therefore, that the stomach of the horse cannot be irritated to make an attempt to vomit, that no such effect generally takes place; for though it is but very seldom that nausea occurs, and perhaps never in a state of nature, yet it may be excited by means of aconite, hellebore, and some other substances, which have caused fruitless efforts to vomit. But the true and principal reason that a horse may be said, naturally not to be able to vomit, arises, in that nature has wisely so constructed the parts, that the very effort to it increases the resistance by the very strong sphincter placed at the mouth of the cardia. Had this resistance not been placed, and every means taken to increase the almost impossibility of vomiting in a horse, it is evident that from the curtain of the palate stopping the opening of the mouth, this action, had it taken place, would have occasioned suffocation. The inner coat of the stomach is composed of two portions, the one cuticular and the other villous. This species of cuticular covering to nearly one half of the stomach, is peculiar to such animals as appear destined to live on grain, as horses, asses, rats, and mice; and this forms a third species of stomach between the true membranous one of graminivorous animals, and the muscular of the carnivorous tribes, and it may be considered in a slight degree, as a species of gizzard, resembling the structure of those animals, as fowls, who have organs to make up for the want of teeth. For a horse has not the means of re-mastication, as in oxen or sheep, nor does he usually masticate his food at first sufficiently to comminute it; for the wants of the constitution stimulate him to a hasty deglutition of his food, which, if there was not some other structure than that common to stomachs in general, would not be sufficiently digested: for the food is solid, and the stomach small; therefore this cuticular coat may be useful, as its insensibility allows it to press 3 K ia 106 Anatomy in a small degree upon the food, and perform a slight of the trituration upon it. This cuticular coat is spread over Horse. the first portion of the stomach, taking in all the great extremity, and forming between a third and half of its extent. It is formed into folds at the cardia in the same manner as at the internal part of the oesophagus; but as soon as it has passed this orifice, these folds take an irregular direction, but are less than those formed on the villous surface. The villous or sensible portion of the stomach, though it occupies more of the length of the stomach, yet perhaps in real extent is little more than half of its surface. It unites with or is connected to the cuticular. Its external surface is firm, and appears as it were a distinct portion, but is only dense cellular substance, which has given rise to the description of four tunics to the stomach. The tunica villosa is so called from its resemblance to the pile of velvet; its fine villi are probably the extreme fine ends of vessels secreting the gastric juice. The villous coat being much larger in extent than the muscular, is thrown into folds which are more considerable than those of the cuticular coat. These are largest at the portion toward the great extremity, and are irregularly waving: towards the duodenum they become less, and when at the pylorus they form a fold that makes a kind of valve to this part of the stomach, preventing the return of the food, and its too speedy passage out. The folds not only hinder the too speedy passage of the food, but by this means apply the gastric juice more certainly to all the parts; but the Outlines. principal end is to increase the secreting surface, which is here more extensive than those of the human *. *Blaine's 107 Bowels. The remainder of the alimentary canal is continued from the lower orifice of the stomach, to the anus, or end of the passage, forming a long canal of different dimensions, called intestines. They are usually divided into small and large. In some animals they hardly merit this distinction, there being but little difference in point of size: but in the horse, the proportion is very different; the small intestines being not much larger than the human, but the large of an immense bulk. This canal is connected through its whole extent to membranous productions of the peritoneum, especially to those called mesentery and mesocolon. The whole canal varies in point of length in different subjects; but is seldom less than 24 yards, and often more. The intestines are contained within a prolongation of the peritoneum, which arises in most instances from the mesentery the two folds of this membrane separate and surround the intestines, forming their external coat. The next coat is muscular, and formed of two layers of fibres, a longitudinal and a circular; the latter are in greater proportion, and by the contraction of these the vermicular motion, called peristaltic, is performed, from the longitudinal fibres slightly shortening them, and the circular diminishing their size. Within this muscular coat there is a quantity of cellular membrane rather more dense than in some other parts; and this used to be regarded as a coat, and was called the nervous, but is only a layer of cellular membrane. The third and inner coat of the intestines is the villous, which is very vascular and sensible. There are no considerable folds of the inner tunic of the intestines, as in the human. In this animal these are rendered unnecessary by the great of the 108 First por. length of his intestines, and the slow passage of the ali- Anatomy ments through them by this length and his position. The first portion of the bowels, which answers to the Horse. duodenum in man, though in the horse it is nearer 20 inches than 12, is attached to the stomach, having its pyloric orifice ending in it; its course in the horse is tion. rather different from that in the human, and by this it acquires a more complete covering from the peritoneum. It hangs loose and pendulous, being attached to the concave surface of the liver, where making a turn, it is fixed to the vertebræ : it then takes the name of jejunum. It appears rather larger in circumference than the other small intestines, and is remarkable for having the pancreatic and biliary ducts penetrating it, sometimes entering it obliquely close together, and sometimes at a distance from each other. 109 The jejunum and ilium differ very little from the Jejunur. same bowels in the human species. 110 The great intestines are very properly so called in Large inthe horse; and as they have very little resemblance to testines. the human large intestines, they require a particular description. The cæcum is situated in the back part of the belly, Cacom. and is a very large canal, which is entered abruptly by the ilium. The fore part of this canal projects forward two or three feet, into a sort of bag of the same size of the colon; but the back part terminates in what is called a blind end. The cæcum usually occupies the right side of the belly, and appears immediately on opening the peritoneum, with its commencement from the colon and ilium in the right iliac region, extending forwards to the right side, with its blind end close to the diaphragm and liver. This termination is not furnished, as in some animals, with an appendix vermiformis, but terminates by a simple blind end. Through the peritoneal covering are seen four muscular longitudinal bands, extending from the extremity along the muscular coat, and dividing the gut into four longitudinal portions. One or two of these are usually covered with fat, and are not so regularly longitudinal as the others. The internal membrane is folded up between the longitudinal bands, and by intersecting them forms numerous cavities called the cells. On the slightest inspection we see a great peculiarity in the form of the cæcum of the horse; and in a more accurate view, are struck with the importance of the structure to this animal, and are led to consider the cacum as little less than a second stomach. This is in fact the case; for the food coming in a macerated mass from the small intestines, is mixed in the cæcum, with the bile and pancreatic juice, and here undergoes a farther change, to which the structure of the cæcum is evidently favourable, as it is fitted to retain the mass for a considerable time within it, and to circulate it through all its parts. It has two blind ends, one forming its basis, and near this enters the ilium; the other forming its point, and extending up towards the diaphragm. From one part of the base the colon commences by a very contracted portion, for the purpose of preventing the entrance of the contents of the ilium, till they have passed through the cæcum. In many animals the cæcum is a very inconsiderable part; in some it has one or more appendicles; in others it is almost entirely wanting; Part II. Horse. of the Horse. The bones which compose the foot of the horse are Anatomy six in number, considering the foot as commencing at the fetlock joint. Of these six bones two are included within the hoof, viz. the coffin-bone, and the navicularbone; and four are situated above the hoof, viz. the Bones. large pastern-bone, the small pastern-bone, and the two sesamoid bones. Anatomy and in all but the horse its use is obscure, and apparentof the ly not very important; but in the horse it is certainly little less than a second stomach, for its whole structure proves, that it is purposely designed that all the food taken in shall be poured into the base of this gut, by the contraction of which it shall be forced towards the apex, and either in its passage or return shall be detained in the cells to be in some way farther acted upon, and to undergo some change necessary to the system. Having undergone this change, whatever it is, it is forced into the colon. 112 Colon. 113 Rectum. The colon commences small from the side of the base of the cæcum; and as the ilium cannot be said to enter it together with the cæcum, as in some animals, there is in the horse no such part as the valve of the colon properly so called. The ilium has, however, a sort of protrusion with its inner membrane, by which in some measure it prevents the return of the contents of the cæ cum. As the colon passes, it is farther contracted, and then enlarges into a very long and large canal, which, after having made nearly the whole circumference of the belly, is again slightly contracted. It then again enlarges, passes again round the belly, and is a third time contracted, just where it ends in the rectum or straight gut. The small intestines rest on the turns of the colon and on the cæcum. The colon is furnished with four ligamentous bands in its large portion, but there are only two in the small portions; these form longitudinal fræna, which are intersected again by internal folds, so as to form the cells of the colon. It is connected and supported in its situation by that portion of the mesentery termed mesocolon. This intestine iз very different in the horse to what it is in most other animals in consequence of its variations in size, being in most other instances of one general size; it is likewise this gut and the cæcum that are the principal seat of the inflammation arising from violent purging medicines. The rectum is the continuation of the colon, and passes backwards from the lumbar vertebræ to the anus. Its muscular coat is thicker than that of the other intestines, and it is thrown internally into cavities by the inner membrane, in some manner similar to the cells of the colon, though less; were it not for this, the intestines might be too constantly stimulated to expel its contents, but by this means the fæces are received and retained till they are collected in a considerable quantity, when they are expelled. The rectum is attached to the spine and sacrum by the peritoneum, is here called mesorectum; but the true fold of peritoneum does not invest its whole portion, but leaves it as it approaches the rectum, which is at this place only covered with the cellular part of it. The mesentery bands of the rectum are very strong, and terminate at the anus in a kind of ligamentary expansion attached to the os coccygis. The anus is the termination of the rectum, and is opened by the force of the peristaltic motion and the consent of the parts, and shut by the muscular band round the extremity of the gut, called the sphincter. It is likewise elevated and retracted by two pair of muscles. CHAP. IV. Of the Foot. In our account of the anatomy of the horse's foot, it will be necessary to describe only one foot, as those belonging to both extremities are similar in structure. We shall begin from above, with the large pasternbone, as this contributes to form what is called the large pastern joint. 114 115 The large pastern-bone, (1, fig. 13, 14, and 15.) is Large pasof an oblong cylindrical form, and, as is the case with tern-bones. all such bones, is smaller in the middle than at either extremity. It articulates above with the lower head of the canon-bone, and below with the upper head of the small pastern-bone. At its upper extremity there are three depressions, one on each side, large and superficial (a, c, fig. 13.) to receive the outer and inner convexity of the lower head of the canon-bone, and one in the middle, b, for receiving the middle narrow convexity of the same bone. The fore part of this bone is slightly rounded, and rough towards its upper extremity, as at d, d, for the firmer attachment of ligaments. Behind, at its back part, it is flatter; and here there is a rough depression (C, fig. 14.) also for the attachment of a ligament that is deep seated, and is fixed to the two sesamoid bones. At the lower extremity the large pasternbone is convex on each side (D, E, fig. 14.) for entering into two concavities of the small pastern-bone; and there is a depression (f, fig. 13.) for the attachment of a tendon. At the lower extremity there is also a roughness on each side at ee, for the insertion of ligaments. Both extremities are covered with very smooth elastic gristle, which is kept constantly moist by the synovia or joint oil. 116 At the upper end of the large pastern-bone, towards Sesamoid the back part, are placed the two sesamoid bones, AA bones. (fig. 14.). These are of an irregular wedge-like form, and are covered with cartilage, articulating both with the canon-bone, and on the back part they are very smooth to admit of a tendon readily sliding over them. The upper edges of these bones on each side have a rough irregular surface, into which is inserted a strong ligament that comes from the upper and back parts of the canon-bone, is fastened separately to each of the sesamoid bones, from which it proceeds downwards and obliquely forward to be inserted into the tendon of the large extensor muscles, (see a a a, fig. 16.) a little below the large pastern-joint. These sesamoid bones are of considerable use in the mechanism of the large pastern-joint. "In consequence of their forming the back part of the large pastern-joint, and articulating with the lower and posterior part of the canon, they contribute very essentially, by always receding whenever the foot comes in contact with the ground, to act as a spring to the animal, and to prevent concussion. All the weight received by the upper head of the large pastern-bone is conveyed to bones below; but a considerable portion of the burden is received by the sesamoid bones. While the animal is at rest, and also during motion, these bones sustain part of the weight; and where the pastern-bones are long and oblique, the sesamoids often receive so much of the weight as to put the on the ligaments violently on the stretch, and occasion lame- Horse's Foot, vol. ii. 3 K 2 The ness Coleman Anatomy of the Horse. 117 The small pastern-bone (2, fig. 13, 14, 15.) is about half the length of the large one, and is as broad as it is long. Besides the two concave depressions, (h, h, fig. 13.) mentioned before, there is a ridge between them, i, Small that enters a correspondent depression, g, in the lower tern.bone. head of the large pastern-bone. The small pasternbone has at the back and upper part (F, fig. 14.) a small projection, for the insertion of a long ligament, that comes from the sesamoid bones. The lower articulating surface is more extensive than the upper, as it is connected with the upper surface of two considerable bones, viz. the navicular and coffin-bone. It is of great consequence to understand the mechanism of the joints that are formed by this connection, as it is on this part that the principal stress of the animal falls. The union of the small pastern-bone with the navicular and coffin-bones, forming what is called the coffin-joint, is one of the principal methods provided by nature to prevent concussion. pas IIS Navicular. bone. 119 Coffin-bone. The navicular-bone (3, fig. 13, 14, 15.) is connect ed above with the back part of the small pastern-bone, and the lower edge of this bone is attached by a large ligament to the back part of the coffin-bone. The navicular-bone is slightly concave, to receive the back part of the lower head of the small pastern-bone. The upper edge of the navicular-bone behind is rough (g, fig. 14.) and thick, for the attachment of the upper ligament; and the lower edge of the navicular-bone receives at the back part a strong flat ligament from the coffinbone, immediately above the insertion of the flexor tendon. The lower surface of the navicular-bone is covered by cartilage, and has a small ridge in its centre, (1, fig. 13.) to be received into a corresponding depression in the long flexor-tendon. This bce may be considered as forming two distinct joints, one of which is composed by the connection of one part of the bone with the tendon of the flexor-muscle, and the other is formed by the connection of another surface of the navicular-bone. The whole weight of the animal, supported by the small pastern-bone, is thrown upon the coffin and navicular bones. Of this weight the coffin-bone receives the greater share; but the navicular-bone receives a considerable portion of it, though this bone does not contribute to prevent concussion so much as Mr Freeman has endeavoured to prove. The navicular-bone, when the hoof touches the ground, descends a little, and thus prevents that concussion which the horse's body would have received if this bone had been immoveably fixed; and when the hoof is again raised from the ground, the elasticity of the parts below the navicular-bone lifts up this bone into its former position, thus acting as a spring in facilitating the motion of the animal. As the weight supported by the navicular-bone of the hind feet is less than that supported by the same bone of the fore feet, their descent in the former is less than in the latter. The organs connected with the navicular-bone of the hind feet are also less subject to disease. The coffin-bone (4, fig. 13, 14, 15.) is so named from its being concealed, or as it were buried within the hoof. It is also sometimes called the foot-bone. On its fore part it is rounded, having very nearly the shape of the external hoof. Its upper surface is slightly hollowed (m, m, fig. 13.) to receive the lower end of the small pastern-bone, with the fore part of which it arti Horse. culates, as it does behind with the fore edge of the na- Anatomy vicular-bone. At the back part the coffin-bone ends of the in two processes on each side, the upper of which are tipped with cartilage. At the upper part of the front of the coffin-bone there is a small protuberance, (w, fig. 13.) extending upwards above the joint, and serving for the insertion of the tendon of the mus cles that extend the foot. Below this the coffin-bone is extremely porous, for the passage of nerves and blood-vessels; and towards the lower part in particular there are about 13 holes, for the transmission of considerable arteries, which go to supply the sensible sole. At the heels and quarters the coffin-bone is still more porous, and is supplied with a greater number of arteries, but these are proportionally smaller. The lower surface of the heels of this bone is also very porous, where it unites with the sensible sole, but the rest of the lower surface is generally smooth. There are here two hollow surfaces, which receive two corresponding rounded parts of the sensible sole. They are unequal, the foremost being the larger. Into the hollow on the back part, the tendon of the flexor-muscle is inserted. (A, fig. 16.). 120 There are seven ligaments belonging to the coffin- Ligaments. joint, of which there are three pairs, and one single. The first pair of ligaments take their origin from the heels of the coffin-bone on each side, and pass obliquely upwards as high as the middle, to which they are attached, and at which part of the small pastern-bone (B, fig. 16.) they are blended with the fibres of the lateral ligaments of the small pastern-joint. The second pair of ligaments on each side arise from the edge of the coffin-bone, near the heels, and pass obliquely forward to be inserted into the middle of the small pasternbone (C, fig. 16.) near the attachment of the extensortendon. The third pair take their origin from the lateral edges of the anterior process of the coffin-bone, and are inserted into the edges of the cartilages. The use of these ligaments is to unite the cartilages more firmly to the coffin-bone. The extensor-tendon being inserted into the upper edge of the anterior process of the coffin-bone, prevents the necessity of a ligament at this part. The single ligament of the coffin-bone is connected with the posterior and inferior concave surface of the coffin-bone, immediately above the insertion of the flexor tendon, and also with the lower edge of the navicular-bone. Besides this ligament there is another attached to the whole of the upper and back part of the navicular-bone, by which means that bone is enabled to support a greater share of the weight that rests upon it. By means of these ligaments this important joint is rendered very strong, while by the elasticity of the cartilages, and the constant supply of lubricating. fluid within the joint, all the motions of the animal are rendered safe and easy. The small pastern-joint is also well secured by means of ligaments, and by the sheath of the flexor-tendon. There are also ligaments proceeding from the sesamoid bones, which enter the sheath of the flexor tendon, and are attached to the small pastern-joint (a, a, a, fig. 16.). "The weight which the sesamoid bones, by means of ligaments sustain, is very different in different horses; and bears no proportion to the bulk and weight of the animal. The pastern-joints of large horses destined for slow motion, are constructed very differently from those |