SCAPULA. 



203 



edge which is often deficient. This marginal surface affords attachment through- 

 out its entire extent to the Serratus Magnus muscle. The subscapular fossa 

 presents a transverse depression at its upper part, called the subscapular angle ; 

 it is in this situation that the fossa is deepest ; so that the thickest part of the 

 Subscapularis muscle lies in a line parallel with the glenoid cavity, and must 

 consequently operate most effectively on the humerus which is contained in 

 that cavity. 



The posterior surface, or dorsum (Fig. 152), is arched from above downwards, 

 alternately convex and concave from side to side. It is subdivided unequally 



Fig. 152. Left Scapula. Posterior Surface, or Dorsum. 

 Co race & 



into two parts by the spine ; the portion above the spine is called the supra- 

 spiuous fossa, and that below it, the infraspinous fossa. 



The supraspinous fossa, the smaller of the two, is concave, smooth, and 

 broader, at the vertebral than at the humeral extremity. It affords attachment 

 by its inner two-thirds to the Supraspinatus muscle. 



