72. THE ARTISTIC ANATOMY OF ANIMALS 



tion of the articular osseous surfaces and the disposition of 

 the fibrous bands that retain them in position. Accordingly, 

 in the description which follows, and also in that of the articu- 

 lations of the posterior limbs, we shall occupy ourselves but 

 very briefly with the details above referred to, so as to devote 

 ourselves especially to the indication of the movements — 

 that is to say, of that which, while easily comprehended 

 on recollection of former studies, presents the greatest 

 interest from the artistic standpoint in these studies in 

 comparative anatomy. 



The Scapulo-Humeral Articulation. — The head of the 

 humerus and the glenoid cavity of the scapula being in 

 contact, the two bones are bound together by a rather loose 

 articular capsule, which is strengthened by the muscles of 

 this region which fulfil the function of active ligaments. 



This articulation, so movable in every direction in the 

 human species, is not so much so in quadrupeds ; the arm in 

 the latter, as also the shoulder, being kept in contact with 

 the lateral region of the thorax by the numerous muscles 

 which surround it. 



Of the movements performed by the humerus, flexion and 

 extension are the most extensive ; those of abduction and 

 adduction are much less so. 



It is necessary, before proceeding further, to determine 

 what the two principal movements which we have just 

 mentioned really are, viz., flexion and extension. 



We know that in man the displacements of the humerus 

 which take place in the antero-posterior direction are known 

 as movement or projection forwards, and movement or pro- 

 jection backwards, respectively. We do not say that 

 the humerus is flexed or extended, because, in reality, on 

 account of the position which the skeleton of the shoulder 

 occupies, it is not able to flex or place itself on the line of 

 prolongation of the scapula with which it articulates. 



In quadrupeds it is not so. The humerus and the scapula 

 are contained in almost the same vertical plane ; and the 

 bone of the arm can take, in relation to the latter, the 

 positions characteristic of flexion and extension — that is, of 

 approach to the scapula and removal from it. 



