180 THE SCAPULA. 



a broad ligament goes out, which becomes narrower where it is 

 fixed to the acromion. 



From the cervix scapulae the third process is produced. 

 The forepart of this is formed into a glenoid cavity, which is 

 of the shape of the longitudinal section of an egg, being broad 

 below and narrow above. Between the margin of this cavity 

 and the forepart of the root of the spine, a large sinuosity is 

 left for the transmission of the supra and infra-spinati muscles ; 

 and on the upper part of this margin we may remark a smooth 

 surface, where the second head of the biceps flexor cubiti has 

 its origin. The root of the margin is rough all around, for the 

 firmer adhesion of the capsular ligament of the articulation, and 

 of the cartilage ; the latter is thick on the margin, but becomes 

 very thin as it is continued towards the middle of the cavity, 

 which it lines all over. 



The medullary vessels enter the scapula near the base of the 

 spine. 



The substance of the scapula, as in all other broad flat 

 bones, is cellular, but of an unequal thickness : for the neck and 

 third process are thick and strong ; the inferior costa, spine, and 

 coracoid process, are of a middle thickness ; and the body is so 

 pressed by the muscles, as to become thin and transparent. 



The scapula and clavicle are joined by plane surfaces, tipped 

 with cartilage ; by which neither bone is allowed any consider- 

 able motion, being tightly tied down by the common capsujar 

 ligament, and by a very strong one which proceeds from the 

 coracoid process ; but divides into two before it is fixed into 

 the clavicle, with such a direction as can either allow this 

 bone to have a small rotation, in which its posterior edge turns 

 more backwards, while the anterior one rises farther forwards ; 

 or it can yield to the forepart of the scapula moving down- 

 wards, while the back part of it is drawn upwards: in both 

 which cases, the oblong, smooth articulated surfaces of the 

 clavicle and scapula are not in the same plane, but stand a 

 little transversely, or across each other, and thereby preserve 

 this joint from luxations, to which it would be subject if either of 

 A/^*rt^r~ 



