Rook VII. ANATOMY OF THE HORSE. 965 



have no proper back, but to be made up of sides and chest. In man, the scapula is in a direct angle with 

 the humerus, but in the horse it does not pass out of the plane of the arm. Its superior surface is fur- 

 nished with a considerable cartilage J, m), by means of which its surface is augmented without weight. 

 The posterior surface ends in a superficial cavity called glenoid, which receives the head of the humerus 

 or arm bone. It is divided in its upper surface by its spine. The shoulder blade, as has been already 

 shown in the exterior conformation, has neither bony nor ligamentous union, but is held in its situation 

 by very powerful muscles, as the serratus major, pectoralis, and others. Its usual situation is to a plane 

 perpendicular to the horizon, at an angle of thirty degrees; and it has a motion in its greatest extent of 

 twenty degrees : hence, as it does not pass beyond the perpendicular backwards, so the more oblique its 

 natural situation, the more extensive ar<* its motions. 



6515. The humerus or arm bone [m) is so concealed by muscles as to be overlooked by a cursory ob. 

 server, and hence the radius or next bone is popularly called the arm. It extends from what is called 

 the point of the shoulder, but which, in fact, is a protuberance of its own to the elbow, forming an angle 

 with the scapula, and extending obliquely backwards as that does forwards. Near its upper extremity it 

 sends off a very powerful head to articulate with the shoulder blade. The motions of the humerus arc 

 necessarily confined to a removal from its inclined point backward to the perpendicular line of the body. 

 When this bone is too long, it carries the fore legs too much under the animal, and if this defect is joined 

 to a shallow upright shoulder, the evil will be increased. It, however, fortunately happens that both the 

 angle and extent of these two parts are usually regulated by each other. 



6316. The fare-arm n n, oo) is composed of the radius .00), and an appendage united to it, which, in 

 man and some animals, forms the ulna n n), but which, as the leg of the horse requires no rotatory 

 motion, was unnecessary in him. Here, however, to keep the link of resemblance in all her children 

 of the higher order, Nature has stretched out a large process; which in the colt is really distinct, and 

 may then deserve the name of ulna; and in the adult horse unites with the radius, and serves as an 

 attachment to muscles. On the slightest inspection of the skeleton, it will appear how much the 

 motions of the fore leg must depend on the length and obliquity of this process; which, acting on the 

 principle of a lever in the extension of the arm, must necessarily, as it is either long or short, make all 

 the difference between a long and a short purchase. The breadth of the arm, as it is called, at this part, 

 will, from this reasoning, be seen to be very important. This bone articulates with the knee by its in- 

 ferior portion. 



6317. The carpus, or wrist, called the knee { pp s , is composed of seven bones, whose principal uses appear 

 to be to extend the surface of attachment of ligaments and tendons, and by their interruptions to lessen 

 the shocks of progression. It may be remarked that all hoofed quadrupeds have the anterior extremities 

 permanently in the state of pronation, or with what is called the back of the wrist turned outwards. 

 The carpal bones articulate with each other, and have one investing capsular ligament, by which means 

 the smallest wound of the knee which penetrates this ligament has the effect of opening the whole joint : 

 hence the quantity of synovia or joint oil which escapes in these cases, and hence also the dangerous con. 

 sequences which ensue. 



strong ligamentary attachment, converted by age into a bony one. Although these additions may some, 

 what increase the surface of attachment, their principal use appears to be to keep up the connection with 

 the digiti, of which they appear the rudiments. In the cow there are no splint bones, but the uniformity 

 is more perfectly kept up by the divided hoof: in her, therefore, the canon branches at its inferior sur- 

 face into condyles for the reception of the two claws. 



6319. The pastern (//). The rest of the extremity below the canon, consists of one phalange only, com- 

 prising all the mechanism, and a double portion of complexity of all the phalanges of the digitated tribes. 

 Four bones enter into its composition with two small sesamoids (ss) to each fetlock ; placed there not 

 only to act as a spring and prevent concussion, but to throw the tendon of the foot which runs over them 

 farther from the centre of motion. The pastern bone is situated obliquely forward, and on this obliquity 

 depends the ease and elasticity of the motion of the animal : nevertheless, when it is too long, it requires 

 great ettbrts in the tendons and ligaments to preserve it in its situation ; and thus long-jointed horses must 

 be more subject to fatigue and to strains than others. 



6320. The lesser pastern or coronary bone \t,v) receives the great pastern, and below expands into a 

 considerable surface articulating with the coffin and navicular bones. 



6321. The coffin bone [w] farms the third phalange, and corresponds in shape with the hoof. It is 

 very porous, and laterally receives two prominent cartilages. It is around the outer surface of this bone 

 that the sensible lamina? are attached ; and the inferior surface receives the flexor tendon. 



6322. The navicular nut, or shuttle bane, is situated at the posterior part of the cottin, and unites with 

 that and the preceding bone. 



6323. The posterior extremities differ much from the anterior, not only in their superior 

 strength, and in the different lengths and directions of the parts, but also, in some degree, 

 in their uses. 



6.324. The femur, or thigh bone (3, 4 1 is the largest of the body, its vast indentations and risings, almost 

 peculiar to it, show the great strength of the muscles inserted into it It articulates with the acetabulum 

 or hip joint by a strong head called the whirl-bone. In this situation it is held not only by a powerful 

 capsular ligament, and still more powerful muscles, but by an admirable contrivance resulting from a 

 ligamentous rope, which springs immediately from the middle of its head, and is firmly fixed within the 

 socket of the joint. In its natural situation it is not perpendicular as the human femur, but inclines to 

 an angle of about forty-five degrees. This bone presents large protuberances for the attachment of very 

 powerful muscles called trochanters. Throughout it exhibits a mechanism uniting the combined qualities 

 of celerity and strength unknown to other animals. The inferior end of this bone is received by its 

 condyles into depressions of the tibia, while the patella, or knee-pan, slides over the anterior portions of 

 both bones. 



6325. The patella (5), which is by farriers called the stifle, is nearly angular, and serves for the insertion 

 of some of the strongest muscles of the thigh , which are then continued down to the leg. It thus appears 

 to act as a pulley. 



6326. The tibia or leg bone (6, 6) is usually, in horsemen's language, called the thigh. It is a bone formed 

 of a large epiphysis, with a small attached part called the fibula {';, a long body, and an irregular inferior 

 end, adapted to the peculiarities in shape of the principal bones of the back, with which it articulates. 

 The obliquity in the situation of this bone corresponds with that of the femur, being as oblique back- 

 wards as the former is forwards. The length of the tibia is a prominent character in all animals of quick 

 progression ; in this respect it corresponds with the fore-arm, and the remarks made on that apply, 

 with even more force, to this — that length is advantageous to the celerity, but less so to the ease, of the 

 motion. 



6327. The fibula (7,7) forms a prominent instance, in common with the splint bones, of what was re- 

 marked in the outset of our osteological detail of the extremities — that many parts, whose uses were not 

 apparent, would be found to be organs of harmony, placed in the body to prevent interruption to the 

 completing the general plan of animal organisation. In this way the fibula appears but a process spring- 

 ing from the posterior part of the tibia, forming but the rudiments of the human bone ol that name. 



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