VERTEBRATA. 33 



hog, and mole, among the insectivora, afford examples of clavicle 

 in its highest degree of development. It is very perfect in the 

 rodentia, as the squirrel, beaver, rabbit, rat, &c. Among the eden- 

 tata, those animals only whose habits are fossorial possess clavicle, 

 as the ant-eater, the dasypus, and the gigantic megatherium ; in 

 the last named animal it presents the peculiarity of being articulated 

 with the first rib instead of the sternum. 



Where the anterior extremity is employed merely for the purpose 

 of progression, we find no clavicle, as in the pachydermata, rumi- 

 nant ia, cetacea, and solipeda. In the carnivora. where there is a 

 slight increase in the range of motion of the anterior extremities, 

 the clavicle exists in a rudimental form, and its development is in 

 proportion to the motion enjoyed ; hence it is small and short in 

 the cat, the bear, and the dog ; in those animals it has no attachment 

 to the sternum or scapula, but lies loose among the muscles. 



Scapula. — This bone forms an essential element of the thoracic 

 extremity, and exists wherever the latter is fully developed, but 

 greatly modified, according to the uses to winch the extremity is 

 applied. The cetacea, in general, have a large scapula of a trian- 

 gular form; the pachydermata, ruminantia, and solipeda, have a 

 long narrow scapula placed perpendicularly on the anterior and 

 lateral part of the chest. In the carnivora and rodentia, where 

 strength and freedom of motion are required, the scapulas are placed 

 obliquely over the ribs; and it is interesting to observe how the 

 obliquity of the glenoid cavity varies with the motions required. 

 This fact has not escaped the observation of the horse-jockey, who 

 is well aware that the upright shoulder is the mark of a stumbling 

 horse. 



Humerus. — When the fore-arm and hand are used for seizing 

 objects, as in apes, many rodentia and carnivora, or for flying, as 

 in the bat, the humerus is formed essentially in accordance with 

 the human type. On the contrary, when the anterior part of the 

 member is but slightly developed, as in the cetacea, the bone is 

 short and thick; and in the whalebone whale, it is nearly as broad 

 as it is long. In the mole it is short, thick, and strong; its tuber- 

 osities greatly developed, and its upper extremity presents two arti- 

 culating surfaces, one for the scapula, and the other for the clavicle. 

 This large size of the bone prevails in all the other fossorial ani- 

 mals, as the mighty megatherium, the pangolins, beavers, ant-eaters, 

 and monotremata. The humerus of the lion is remarkable for 

 being perforated by the brachial artery and nerve, in order to avoid 

 being crushed by the huge and powerful mass of muscles exhibited 

 in this part of the economy of the king of beasts. 



Fore-arm. — The radius and ulna are very short in the cetaceans, 

 and in most of them consolidated too-ether at both extremities. In 

 the cheiroptera they are long, slender, and firmly united, to accord 

 with their mode of progression by flight; in some the olecranon is 

 wholly absent, and in others, as the vampyre, it exists in the form 

 of a patella. The ruminants and solipeds have these bones con- 

 7 — ff cvers 3 



