460 



PROP. W. J. SOLLAS ON A NEW SPECIES OF PLESIOSATJRUS 



The Scapula. 



This (fig. 5) consists of a ventral plate, from the outer lateral margin 

 of which a lateral plate arises and ascends towards the dorsal surface, 

 its plane being inclined to that of the ventral plate at an angle of 

 about 90°. The ventral plate is longer than broad, thicker behind 

 than in front, truncated by a slightly convex edge anteriorly, 

 bounded by a widely open Y-shaped margin behind, the inner stroke 

 (cr) of the " V " representing its articulation with the coracoid, the 

 outer stroke (r p) its share in the glenoid cavity for the humerus. The 



Fig. 5. — Diagram of Bight Scapula. (Drawn reversed, scale J.) 



a 



inner lateral margin is concave, the outer straight ; and from along its 

 whole length the lateral plate arises. The latter is like a long sca- 

 lene triangle in shape, the apex lying in front, the longest side being 

 that common to it and the ventral plate, and the next longest its 

 outer edge ; the base of the triangle is not a straight line, but a deep 

 concave curve arising from the anterior edge of the glenoid cavity, 

 passing forwards and upwards and then backwards to the end of the 

 outer edge. The lateral plate, when complete, is not bounded by a 

 simple outer or upper margin, as here described, but is prolonged 

 upwards along its posterior third into a thin narrow ascending pro- 

 cess : this process is broken off both scapula? in our specimen ; and 

 the posterior third of the outer edge of the lateral plate is conse- 

 quently a surface of fracture. 



Dimensions of the Scapula. 



inches. 



Length of outer edge of ventral plate (fig. 5, ap) 8*1 



Breadth at distal end (ib. a b) 2*4 



Length of chord of concave inner margin (ib. be) 5*05 



Height of arc of concave inner margin (ib. cl) 1*2 



Length of articular surface for coracoid (ib. cr) 2-2 



Length of articular surface for humerus (ib. rp) 1»9 



Length of chord of posterior concavity of ascending plate 



(ib. m n) 2-1 



Height of arc of posterior concavity of ascending plate 



(ib. mn) , 1-0 



