862 



PACHYDERMATA. 



Fig. 474. 



Skeleton of Hippopotamus. 



breadth constitute a kind of osseous case, en- 

 closing a considerable portion of the abdominal 

 cavity, and calculated to give origin to muscles 

 of power proportioned to its ponderous con- 

 tents. 



In the Hyrax, dissected by Pallas, there 

 were twenty-two ribs on the left side and only 

 twenty-one on the right : .of these seven were 

 true ribs, six false attached to the sternum by 

 the intervention of costal cartilages, and the 

 rest merely imbedded in the muscles of the 

 flanks. The sternum consisted of six pieces, 

 of which the last or ensiform was further pro- 

 longed by a spathulate cartilage. 



In the Tapir the ribs are twenty in number 

 on each side, whilst there are but four lumbar 

 vertebra. The Elephant, likewise, has twenty 

 pairs of ribs and only three lumbar vertebrae. 

 The Rhinoceros has nineteen pairs of ribs, and 

 the Hog only fourteen. 



The sternum is of considerable length and 

 compressed laterally. In many genera, more- 

 over, it is prolonged in front to a considerable 

 distance, in order to allow more ample space 

 for the attachment of muscles. 



Anterior extremities. The limbs of the 

 Pachydermata are necessarily constructed more 

 with a view to ensure strength adequate to sus- 

 tain their ponderous bulk than to permit of 

 agile and active movements. The smaller 

 genera, indeed, such as the Suidse, have their 

 bones so arranged as to permit of considerable 

 fleetness in running, but in the more colossal 

 genera the condition of the extremities secures 

 support at the expense of speed, and flexibility 

 is sacrificed to solidity and firmness. 



Scapula. The shoulder-blade of the Ele- 

 phant, independently of its size, might be 

 distinguished from that of any other living 

 animal by the following circumstances. When 

 in situ, its posterior side, which is deeply con- 

 cave, is by far the shortest of the three, while 

 the anterior and spinal costae are of nearly 

 equal length. In consequence of the preceding 

 circumstance this scapula is broader in propor- 

 tion to its length than that of any other 

 large quadruped, and, moreover, the spine of 

 this bone, besides its acromial process, has 

 towards its middle a broad sickle-shaped pro- 

 jection, looking backwards and spreading over 



the infra-spinatus muscle. In all other Pachy- 

 dermata the shape of the scapula is that of an 

 elongated triangle, with the angles of the base 

 much rounded off and the spine very short in 

 proportion to the extent of the dorsum ; never- 

 theless, in the Rhinoceros there is a falciform 

 process projecting from the spine something 

 like that of the Elephant, and both in the 

 Hippopotamus and the Tapir rudiments of a 

 coracoid process. The scapula of the Tapir (Jig. 

 475) is also remarkable for a deep and almost 

 circular notch between the rudimentary acro- 

 mion and its anterior costa. 



Clavicle. None of the Pachydermata have 

 the slightest rudiment of a clavicle, an arrange- 

 ment which permits the anterior shoulders to 

 be closely approximated beneath the thorax, 

 and thus brought nearer to the centre of gravity. 



Humerus. The humerus is in all cases short, 

 massive, and remarkable for the size and strength 

 of the ridges and prominences for the origin 

 and insertion of the muscles connected with it. 

 The head of the bone which articulates with 

 the scapula is very flat, and although large, 

 forms but a very small proportion of its scapular 

 extremity, the rest being made up of enormous 

 protuberances, to which are affixed the muscles 

 of the shoulder. ( Figs. 474 and 475.) 



The lower articulating surface is a simple 

 pulley, articulating with the conjoined heads 

 of the radius and ulna, so as to admit of flexion 

 and extension only, no movements of pronation 

 or supination being here admissible. 



The humerus of the Elephant (fig. 464) is 

 distinguishable from that of all other quadrupeds 

 by the prodigious extent of the external condyle, 

 which extends upwards nearly one-third of the 

 length of the bone, where it terminates abruptly 

 so as to give a square form to this part of the 

 bone. 



Radius and ulna. As the position of the 

 fore-arm in the Pachydermata is permanently 

 that of pronation, no arrangement has been 

 made in any instance to articulate the radius 

 with the ulna by means of a moveable joint, a 

 certain degree of elasticity (the result of liga- 

 mentous connection) being all the motion 

 allowed even where the separation between the 

 two bones is most complete. Sometimes, in- 

 deed, as in the case of the Hippopotamus and 



