THE SCAPULA. 107 



mial end of the clavicle is flat and presents an articular 

 facet for articulation with the acromion process. The 

 plane of the facet is oblique, the bone being beveled at 

 the expense of the under surface. The sternal end of 

 the clavicle presents a trilateral articular surface continu- 

 ous with that for the first costal cartilage ; it articulates 

 with the sternum by means of an interarticular fibro- 

 cartilage. The clavicle develops by two centres, one for 

 the sternal end, the other for the shaft. A third centre 

 is frequently found close to the articular surface for the 

 scapula. 



THE SCAPULA. 



The scapulae, or shoulder-blades, are two flat bone 

 which, with the clavicles, form the osseous shoulder-girdle. 

 Each is triangular in shape and presents for examination 

 an anterior and posterior surface ; superior, vertebral, and 

 axillary borders ; superior angle, inferior angle, and base. 

 The posterior surface is slightly convex from above down- 

 ward, and is divided into two fossae by the spine, a shelf- 

 like plate of bone, which projects at an angle of 50 

 degrees from the posterior surface of the scapula at its 

 upper third. Thespine of the scapula then curves for- 

 ward and outward, and terminates in a flattened process 

 of bone called the acromion, which articulates with, the 

 clavicfe The spine limits the supra-spinous fossa below 

 and the infra-spinous fossa above. It begins at the ver- 

 tebral border at a flattened surface, gradually becomes 

 broader, and stops about half an inch from the base of 

 the scapula, in fact, at the neck of the bone. Its upper 

 edge affords attachment to the trapezius muscle, its lower 

 edge to the deltoid. The acromion process is the con- 

 tinuation of the spine; it arches over the glenoid cavity, 

 and presents for examination an upper and lower surface, 

 an anterior and posterior border, and an apex. The 



