464 PEOFESSOE J. ANDEESON ON THE 



loped, first as a thin plate, rather deeply concave anteriorly, almost resembling an 

 osseous bulla from behind forwards, terminating in only a slightly thickened extremity 

 that overhangs the head of the humerus in close apposition to it. Posterior to and 

 above this, there is a prominent metacromial process directed downwards and back- 

 wards, more developed than in Gymnura, but of the same character. 



The notch at the inferior extremity of the mesoscapula, formed by the downwardly 

 projecting acromion, is vei^ deep. The coracoid appears to be the elongated anterior 

 process of the glenoid cavity, which projects over the anterior aspect of the head of the 

 humerus. The glenoid cavity thus presents a cup-shaped hollow, behind which it is 

 continuous with the coracoid. The postscapular surface is oblong and slightly concave, 

 due to the outward folding of its posterior half. Viewed laterally, its inferior half is 

 hidden by the lower portion of the spine and by the acromion. The lower end of the 

 posterior margin terminates in a rather prominent process, which is separated from the 

 glenoid cavity by a faint depression. The prescapular surface presents a well-marked 

 fun-ow from above downwards, which divides the bone into two portions : — the posterior 

 being a very elongated triangular ; aud the anterior small and defined posteriorly by the 

 furrow, and anteriorly by its convex margin. The inner aspect of the scapula is marked 

 by a mesial longitudinal furrow, corresponding to the situation of the spine, anteriorly 

 by a faint ridge on the position of the furrow on the opposite side of the prsescapula, 

 and posteriorly by another ridge produced by the furrow on the external aspect of the 

 postscapular surface. The inner aspect of the bone thus presents four surfaces, corre- 

 sponding to those on its external face. The postscapular ridge has a small ridge-like 

 process posterior to its inferior end ; and the prescapular ridge runs into the coracoid. 

 In a young individual the acromion of one scapula has broken off from the mesoscapula, 

 showing that it is of considerable extent, and that the bulla-like portion of that part of 

 the bone is wholly acromial ; and in the other scapula of the same animal there is a 

 fracture at the same place on the mesoscapula, but the acromion has not become 

 entirely detached. 



The clavicle is a rather slender bone, with an obtuse inward and forward curve at its 

 vertebral end. At its sternal extremity it is separated from the praesternum by a distinct 

 osseous prsecoracoid of considerable size ; but I cannot detect any mesoscapular segment. 



The prcesternum (fig. 19), viewed in front, is laterally dilated in its upper half into two 

 wings, separated from each other by a well-developed longitudinal ridge, while the wings 

 on either side of it are slightly concave. The lower half is a laterally compressed rod 

 of bone, on to the anterior aspect of which the prsesternal ridge is continued. Viewed 

 from the side, the praesternum is only slightly broader above than below (in its rod-like 

 portion), and its posterior surface is concave. The mesosternum consists of four pieces, 

 of which the first is a short, laterally compressed rod like the posterior half of the prae- 

 sternum, but slightly thicker at its two extremities. From the second to the third the 

 pieces gain in lateral expansion ; and the last is a quadrangular flat piece of bone. The 



