THOEACIC LIMBS 527 



anterior, or cervical, end of the thorax. Each scapula has a flat 

 inner surface applied to the thorax and a keeled outer surface facing 

 directly outward. The outline of the scapula is that of an elongated 

 triangle, and it is so placed in the skeleton that the edge which forms 

 the base of the triangle is above the level of the spinous processes of 

 the thoracic vertebrae and faces upward and also slightly backward 

 toward the tail ; the shorter border is in front, the longer, straighter 

 border behind ; and the truncated lower angle, the apex, points down- 

 ward and forward. The long axis of the triangle is, therefore, directed 

 from above obliquely downward and forward. The outer surface of 

 the scapula is well covered with muscles ; it forms the prominent 

 shoulder, and can be plainly seen, felt, and outlined through the skin. 

 Except for the interposition of several layers of muscles, the inner 

 surface is applied to the convexity formed by the anterior ribs. The 

 scapula has an extended range of motion, and may assume very 

 different positions in the various movements of the anterior extrem- 

 ities. This is due to the fact that it is but loosely joined to the axial 

 skeleton. It is attached by muscles to the ribs, to the head, to the 

 cervical and thoracic vertebrae, and by fascia, with the aid of the 

 rudimentary clavicle, to the sternum. It articulates by the shoulder- 

 joint with the bone of the arm, the humerus, with which and the 

 bones of the forearm it is connected by many and important muscles. 

 The scapula consists of a main upper portion, the body, separated by 

 a constriction, the neck, from a very small lower and thicker portion, 

 the head. 



The Body is a thin translucent plate composed for the most part 

 of two layers of compact bony tissue separated by a thin layer of 

 caucellous tissue. It presents for examination two surfaces, three 

 borders, and three angles. 



The outer surface (Fig. 418) may be recognized as the surface 

 supporting the high keel-like ridge. It is irregularly triangular, 

 about one-third longer than wide. The upper edge, or base, is arcuate, 

 and directed somewhat obliquely to the long axis of the surface, so 

 that the anterior border is shorter than the posterior. The lower end 

 is continuous with the neck, and is comparatively narrow, its width 

 being less than a fourth of the greatest width. The greatest width is 

 not at the upper border, but considerably below it. The outer surface 

 is bounded above by the vertebral border, in front by the anterior 



