THE UPPER LIMB IN MAN. 235 



g. The scapula and clavicle are more harmoniously 

 developed in the human than in the animal shoulder. 



h. The strongly marked sigmoidal curvature of the human 

 clavicle, and the peculiar curvatures of the scapular spine 

 and acromion, are related to the transverse and horizontal 

 direction of the axis of the shoulder ; for no animal has the 

 acromial extremity of the clavicle fully developed, nor can the 

 axis of the acromial portions of their opposite clavicles coin- 

 cide with a common transverse line. The coincident transverse 

 line of the opposite acromio-clavicular axes in man lies above 

 the axes of the shoulders, and is parallel to them. 



i. The peculiar carriage of the human shoulders (the 

 square shoulder) is due — 



1st. To the position of the scapulas on the posterior (neural) 

 aspect of the trunk. 



2d. To the rectangular relations of the axes of the shoulders 

 to the axis of the trunk ; and 



3d. To the curvatures of the clavicles. 

 />-. The movements of the human shoulder are — 

 1st. Rotation from behind forwards, and from before back- 

 wards, with the clavicle as a radius. 



2d. Rotation from below upwards, and from above down- 

 wards, also with the clavicle as a radius. These two rectangular 

 movements are so co-ordinated that each rotation may take 

 place, more or less freely, in any given angular position of the 

 other. The primary plane of the antero-posterior movement 

 ia the horizontal plane of the shoulder; and the primary 

 plane of the movement from below upwards, is the transverse 

 vertical plane in which the axis of the shoulder lies. 



/. As contrasted with the movements of the human 

 shoulder, we find that on account of the transverse obliquity 

 of the areas of the shoulder in the mammal, and the lateral 

 position of its scapuhe, along with its horizontal attitude, 

 the vertical rotation in man becomes an antero-posterior in 



