464 PROFESSOR J. ANDERSON 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 very 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 
furrow from above downwards, which divides the bone into two portions :—the posterior 
being a very elongated triangular; and 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 prescapula, 
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 presternum by a distinct 
osseous preecoracoid of considerable size; but I cannot detect any mesoscapular segment. 
The presternum (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 presternal ridge is continued. Viewed 
from the side, the presternum is only slightly broader above than below (in its rod-like 
portion), and its posterior surface is concave. The mesosternwm consists of four pieces, 
of which the first is a short, laterally compressed rod like the posterior half of the pre- 
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 
