THE SKELETAL SYSTEM 



247 



The Appendicular Skeleton in Man 



I. Upper Limb. The upper limb is divided into four regions, pectoral 

 girdle, upper arm, forearm, and hand. The pectoral girdle consists of 

 two bones, the scapula and clavicle or collar bone. 



The Scapula. The scapula or shoulder blade is a triangular bone 

 embedded in the muscles of the back and forming the chief skeletal support 

 of the shoulder. It consists of a flattened body with two processes, the 

 coracoid and the acromion. The dorsal surface of the scapula is divided 



PRIMITIVE 

 REPTILES 



MAMMAL-LI KE 

 REPTILE 



Fig. 205. — A series of skeletons of hands and feet of tetrapods showing the con- 

 jectured evolution of the human hand and foot. The human hand is evidently less 

 specialized than is the foot. (Redrawn after Romer's "Man and the Vertebrates," 

 University of Chicago Press.) 



unequally by the spine into a smaller upper supraspinous fossa containing 

 the supraspinatus muscle, and a larger lower infraspinous fossa in which 

 is the infraspinatus muscle. The concave inner or costal surface of the 

 scapula lodges the subscapularis muscle. The three borders of the 

 scapula are the superior, vertebral, and axillary. 



At the outer or lateral angle of the scapula is a shallow depression, 

 the glenoid fossa, which provides the articulating surface for the "bend" 

 of the humerus. The spine of the scapula terminates laterally in the 

 acromion process, where it forms the summit of the shoulder and serves as 

 the origin of parts of the deltoid and trapezius muscles. The clavicle 

 articulates in a concavity in the acromion process. The coracoid process, 

 shaped like a bent finger, projects laterally and forward from the "neck" 

 of the scapula. 



