in lelithyosauria and Sauropterygia. 2b*5 



rated bone, I find the ventral end to comprise a stout, posterior part 

 of an approximately semi- ellipsoidal figure, having its major axis, 

 10'5 cm. long, much nearer the inner border, which does not greatly 

 vary from a straight line. The minor axis, 4'3 cm. long, is distant 

 4'6 cm. from the posterior vertex of the ellipsoid, towards which the 

 thickness of the bone rapidly diminishes. The reduction of thick- 

 ness forwards is less rapid, the width across the end, between the 

 inner and the outer surface, being T8 cm., at the anterior vertex of 

 the ellipsoid. From this point forwards the thickness of the bone 

 continues to decrease to the anterior border of the bone, with which 

 this part of the ventral end makes an angle. At its anterior termi- 

 nation here the thickness of the ventral end is only O8 cm. The 

 surface texture of this end has a granular character suggestive of a 

 former cartilaginous crust. This granulation is coarser in the 

 narrower anterior part. 



When this scapula is stood on its ventral end on a flat horizontal 

 surface, as on a table, and viewed perpendicularly to one of its 

 surfaces (preferably the inner surface), the profile of this end of the 

 bone comprises a middle, horizontal segment, from both ends of 

 which the contour rises angularly ; its posterior branch includes 

 with the horizontal direction of the middle part (produced) an angle 

 of about 35 ; and its anterior branch includes with the same hori- 

 zontal line an angle of 65. 



This different direction of the parts of the profile apparently has 

 suggested to Professor H. G. Seeley a threefold division, in which 

 each part had a distinct separate office. A critical examination of 

 the surface of the end shows, I think, that the idea of a tripartite 

 division of this end is illusory, and that this end comprises only two 

 parts, one posterior, glenoid, diarthrodial segment ; the other, an 

 anterior synchondrosial segment, which articulated with the 

 coracoid. 



The outer surface of the scapula near its ventral end is sinuous ; 

 convex in its posterior third, where the bone is stoutest ; and con- 

 cave in its anterior two -thirds, where the bone becomes thin, the 

 concavity here being chiefly due to the outward trend of the surface 

 towards the anterior border which gives to this part a thin, lip-like, 

 angularly projecting figure where the ventral and anterior borders 

 meet. 



In conformity with the ventral end of the scapula, the correspond- 

 ing outer border of the roughly quadrilateral coracoid exhibits a 

 stout posterior part, its complement of the fossa glenoidalis ; and 

 a thinner anterior part which encroaches on the anterior border by 

 truncation of the ant ero- external angle, for synchondrosial union 

 with the scapula. 



Bearing in mind that the bones composing the Ichthyosaurian 



