718 



SOLIPEDA. 



head is in a very material degree supported ; 

 posteriorly, the spinous processes of the dor- 

 sal region become gradually shorter, and their 

 extremities broad and flattened, so as gradu- 

 ally to approximate in their shape those of 

 the lumbar region. 



The vertebrce of the loins are, in the Soli- 

 pecla, usually six in number: such is the case 

 in the horse, zebra, and quagga; but in the 

 ass there are but five lumbar vertebrae. This 

 portion of the vertebral column is, in the 

 class under consideration, possessed of great 

 strength ; the bodies of the vertebrae are 

 broad and firmly bound together ; the trans- 

 verse processes of remarkable length and 

 power ; the articulating apophyses strong and 

 broadly connected with each other, while the 

 spinous processes, which are of great breadth, 

 are either quite straight or inclined forward. 



The sacrum in all the Solipeda is composed 

 of five vertebrae consolidated into one piece, 

 and, with that exception, scarcely different 

 from the vertebral pieces that immediately 

 precede and follow it. In the horse, as in 

 most Quadrupeds, the sacrum is much nar- 

 rower in proportion than in the human sub- 

 ject, and forming, moreover, a continuous 

 straight line with the rest of the spinal column, 

 allows of much more freedom of motion in 

 this part of the skeleton than is possible in 

 the human subject; and this is much increased 

 by the obliquity of the junction between the 

 sacrum and the iliac bones. The articulation, 

 moreover, between the last lumbar vertebra 

 and the sacrum, still further adds to the 

 mobility of these parts ; for in the horse, the 

 oblique processes of that vertebra are con- 

 nected with the sacrum by means of articu- 

 lating surfaces of very large size, so that from 

 the combination of all these circumstances, 

 there is a springiness given to this region of 

 the vertebral column, the importance of which, 

 in galloping or leaping, is at once conspicuous. 



The caudal vertebra in the solipeds vary 

 in number from seventeen to twenty-one ; but 

 of these, the upper ones only resemble true 

 vertebrae. Even in the first caudal vertebra, 

 the inferior oblique processes become ob- 

 literated, and as we descend, all the vertebral 

 apophyses rapidly disappear : at the second 

 bone of the tail, the spinal laminae no longer 

 rise high enough to enclose the spinal canal ; 

 but resemble two short processes; and at 

 about the fifth or sixth, all vestiges of them 

 are lost, nothing remaining but the bodies of 

 the vertebrae of a cylindrical shape and slightly 

 enlarged at each extremity, until we approach 

 the last, where all regularity of form is lost. 



Thorax. The sternum of the solipeds is 

 considerably compressed towards its anterior 

 extremity, which is moreover prolonged to 

 some extent beyond the insertion of the first 

 rib, so as to give to the whole chest a cari- 

 nated appearance, which forcibly reminds the 

 anatomist of the thorax of a bird. Posteriorly, 

 the carinated form disappears, and the sternum 

 becomes broad and flattened where it receives 

 the cartilages of the posterior true ribs. The 

 sternum of the horse is composed of several 



osseous pieces bound together by strong liga- 

 mentous and cartilaginous connections. 



The ribs are eighteen in number, so that 

 the thorax is prolonged very far backwards 

 towards the pelvis. The anterior ribs are 

 broad and massive ; but of these, eight only 

 are attached to the sternum : the posterior or 

 false ribs gradually become more slender as 

 they recede backwards to expand over the 

 cavity of the abdomen. 



Anterior extremity. The frame-work of the 

 shoulder in the Solipeda, as in all ungulate 

 quadrupeds, is composed of the scapula only ; 

 the coracoid apparatus being dubiously repre- 

 sented by a rudimentary apophysis, and the 

 clavicle is totally wanting in circumstances 

 which allow of the close approximation of the 

 shoulder blades to the sides of the chest, and 

 thus cause the weight of the body to be trans- 

 mitted perpendicularly to the ground. 



The shape of the scapula (/g.498. o) is al- 

 most that of an isosceles triangle, the spinal 

 costa, which is about half the length of the 

 other two, having its angles rounded off. 

 The spine of the scapula is prominently deve- 

 loped, and towards its upper third, projects 

 posteriorly, so as to form a considerable re- 

 curved process (i) ; as it approaches the neck 

 of the bone, however, the scapular spine be- 

 comes quite obliterated, spreading out upon 

 the margin of the glenoid cavity (//), so that 

 no acromion process exists in these quadru- 

 peds. 



The humerus (fig. 498. <?, b, k) is short, but 

 of great strength, and the muscular imprints 

 strongly marked. 



The forearm is almost exclusively formed by 

 the radius (fig. 498. o,r), the strength of which 

 is in accordance with the enormous weight it 

 has to sustain, while the ulna is reduced to a 

 mere appendage (/g.498.s, t, u), which in the 

 adult animal is completely consolidated with 

 its posterior surface, the line of demarcation 

 between the two being only indicated by a fur- 

 row which, towards the upper extremity of 

 the forearm, deepens into a slight fissure. 

 The olecranon process is, however, of large 

 size, and, by its projection posteriorly, affords 

 a powerful purchase to the massive extensor 

 muscles inserted into this portion of the limb. 

 From the above arrangement of the bones of 

 the forearm, it is manifest that all movements 

 of pronation and supination are here out of 

 the question ; the limb must remain constantly 

 fixed in a state of pronation, in which con- 

 dition it is anchylosed, and thus acquires a 

 firmness and steadiness which would be quite 

 incompatible with more extensive movements. 



The carpus in the Solipeda consists of seven 

 bones arranged in two rows, of which four 

 are situated in the first, and three in the 

 second. 



The upper series consists of the representa- 

 tive of the os scaphoides of the human subject 

 {fig. 498. w) ; of the os lunare (x) ; of the 

 cuneiforme (^/) ; and of the os pisiforme (z). 



In the lower series, the 0,9 trapezium, which 

 supports the thumb of the human hand, does 

 not exist in the horse ; but the trapezoid (not 



