142 



THE SKELETON. 



inward, then, becoming smaller, it changes its direction and passes forward and 

 outward. The ascending portion, flattened from before backward, presents in 

 front a smooth, concave surface over which passes the Subscapularis muscle. The 

 horizontal portion is flattened from above downward, its upper surface is convex 

 and irregular, and gives attachment to the Pectoralis minor ; its under surface is 

 smooth ; its inner border is rough, and gives attachment to the Pectoralis minor ; 

 its outer border is also rough for the coraco-acromial ligament, while the apex is 

 embraced by the conjoined tendon of origin of the short head of the Biceps and 

 of the Coraco-brachialis and gives attachment to the Costo-coracoid ligament. At 

 the inner side of the root of the coracoid process is "a rough impression for the 

 attachment of the conoid ligament ; and running from it obliquely forward and 

 outward on the upper surface of the horizontal portion, an elevated ridge for the 

 attachment of the trapezoid ligament. 



FIG. 96. Plan of the development of the scapula. By seven centres. The epiphyses (except one for the 

 coracoid process) appear from fifteen to seventeen years, and unite between twenty-two and twenty-five years 

 of age. 



Structure. In the head, processes, and all the thickened parts of the bone the 

 scapula is composed of cancellous tissue, while in the rest of its extent it is com- 

 posed of a thin layer of dense, compact tissue. The centre part of the supra- 

 spinous fossa and the upper part of the infra-spinous fossa, but especially the 

 former, are usually so thin as to be semitransparent ; occasionally the bone is 

 found wanting in this situation, and the adjacent muscles come into contact. 



Development (Fig. 96). By seven or more centres : one for the body, two for 

 the coracoid process, two for the acromion, one for the vertebral border, and one 

 for the inferior angle. 



Ossification of the body of the scapula commences about the second month of 

 foetal life by the formation of an irregular quadrilateral plate of bone immediately 

 behind the glenoid cavity. This plate extends itself so as to form the chief part . 

 of the bone, the spine growing up from its posterior surface about the third month. 



