OSTEOLOGY AND ARTHROLOGY 25 



to execute. But the movements which those muscles 

 produce (more especially the rotation of the humerus) are, 

 in quadrupeds, less extensive than in the human being ; 

 and, consequently, the muscles which produce them are, 

 proportionally, less strongly developed. The inferior angle 

 (superior and external in man), situated at the junction of 

 the cervical and axillary borders, presents the glenoid 

 cavity, which, looking downwards, receives the articular 

 surface of the superior extremity of the bone of the arm — 

 that is to say, the head of the humerus. Above this 

 cavity, on the lower part of the cervical border, is situated 

 a tubercle which reminds us of the coracoid process of 

 the human scapula. The region occupied by the glenoid 

 cavity is separated from the body of the bone by a constric- 

 tion — the neck of the scapula. 



In birds the scapula is elongated in a direction parallel to 

 the vertebral column, and very narrow in the opposite 

 (Fig. 18) ; it is also flat, and has no spine. Its coracoid 

 process is represented by a peculiar bone — the coracoidean 

 or coracoid bone — which we shall describe later on when 

 we come to the study of the clavicle and of the anterior 

 region of the shoulder (see p. 26). 



The Clavicle. — The clavicle is found only in the human 

 being, and in animals whose anterior limbs, possessing 

 great freedom of movement in all directions, require 

 that the scapula should possess a point of support which, 

 while affording this, can be displaced with it, or draw it 

 in certain directions. Now, this point of support is 

 furnished by the clavicle. 



In S.nimals possessed of hoofs (ungulates), such as the 

 sheep, ox, and horse, the clavicle does not exist. Indeed, 

 in them the freedom of movement of the anterior limbs is 

 limited ; they move by projection in the forward and 

 backward directions only ; they merely fulfil the functions 

 of giving support to and carrying about the body. The 

 clavicle is rudimentary in the cat and the dog ; in the cat 

 it is a small, elongated bone (Fig. 16), 2 centimetres in 

 length, thin and curved, connected with the sternum and 

 the scapula by ligamentous bundles. In the dog it is 



