ANTERIOR MEMBER. 201 



A. The Shoulder. 



Several authors have intentionally united the description of the 

 shoulder with that of the arm, because of the fact that, in relation 

 with the exterior, there exists between them no definite line of separa- 

 tion, and that, in relation with their functions, they are intimately 

 united. There is, nevertheless, no more reason for con founding these 

 regions than there is for uniting the croup with the thigh, the back 

 with the loins, or the neck with the head. We shall therefore study 

 them separately. 



Situation; Limits; Anatomical Base. Situated between 

 the neck and the sides of the thorax, the withers and the arm, the 

 shoulder occupies, without any precise demarcation, the lateral and 

 anterior region of the chest. 



The scapula is flat and triangular, and is provided with a strong spine on its 

 external surface and a wide cartilage of prolongation at its superior border. It 

 thus forms the osseous base of the shoulder, and gives attachment to two kinds 

 of muscles, which, with respect to the anterior member, can be distinguished as 

 extrinsic and intrinsic. Besides, this bone participates by its inferior extremity 

 in the formation of an articulation very mobile and at the centre of the move- 

 ments of the arm. 



The extrinsic muscles originate from the vertebrae, the ribs, and the sternum. 

 Viewed only as to their action upon the shoulder, their function is to fix the 

 latter to the trunk and regulate its displacements. 



The intrinsic muscles embrace and sustain the scapulo-humeral arthrodia, 

 and act exclusively upon the arm, except three which extend to the forearm 

 (the long and short flexors and the great extensor of the forearm). These 

 intrinsic muscles determine most of the movements of the humerus, and carry 

 this bone into extension, flexion, abduction, and adduction. They also oppose 

 the closing of the articular angle during station, and maintain in proper relation 

 the two bones which form it. 



Form. It is difficult to assign a geometrical form to the shoulder 

 on account of its intimate connections with the thorax, the neck, the 

 withers, and the arm. In lean subjects, the most salient parts of its 

 conformation are very markedly delineated underneath the skin : in 

 front, its anterior border projects from the base of the neck ; above, its 

 cartilage is indicated by a curve parallel with the superior line of the 

 withers ; on its external face a longitudinal crest, formed by the acro- 

 mion spine, extends from above to below ; behind, a less marked 

 furrow separates it from the thorax ; in front and below, a round, 

 voluminous eminence, improperly called the point of the shoulder, 1 



1 It is formed, in fact, by the superior extremity of the humerus, and merits much more 

 appropriately the name point of the arm, under which Bourgelat described it. 



