110 MAEINE EEPTILES OF THE OXFORD CLAY. 



inwards ; it is triangular in outline and its nearly flat surface bears rugosities wliich 

 indicate that in life it was capped with cartilage. The glenoid facet looks backwards 

 and outwards, making an angle of about 90° with that for the coracoid; in outline 

 it is half an oval, the line of union with the other surface being the short diameter of 

 the oval ; it is only slightly concave and nearly smooth in specimens in which ossifi- 

 cation seems to be approaching completion, but in younger animals it may be 

 roughened, and was no doubt covered with cartilage. The shaft of the posterior bar 

 is almost triangular in section : one angle forms the sharp outer border of the coraco- 

 scapular fenestra ; the lower angle forms a strong ridge which extends on the outer 

 (lower) face of the bone from the anterior angle of the glenoid cavity to the anterior 

 angle of the blade, forming the line of division between the dorsal and ventral portions. 

 The dorsal arm is directed a little backwards ; it rises from a broad base, but narrows 

 above, the anterior and posterior borders becoming nearly parallel ; its upper supra- 

 scapular border is terminated by a narrow concave surface, indicating the presence of a 

 cap of cartilage. The size and shape of the ventral ramus of the scapula vary both 

 according to the species and with the age of the individual. Probably in all specimens 

 of fully grown animals the scapulae of opposite sides meet in median suture and 

 extend back to meet the anterior median prolongations of the coracoids. In the type 

 specimen of M. j^laii/clis, in which growth was complete, the scapula (PI. VI. fig. 3 ; 

 text-fig. 68) has a broad ventral plate, of which the concave upper surface is continuous 

 with the upper surface of the dorsal ramus, but the ventral face is sharply separated 

 from the outer face by the ridge-like angle referred to above. The ventral plates of the 

 opposite scapulae meet in median suture in their posterior half only, \\here they are 

 much thickened ; the thin anterior portions are separated by a deep notch, the posterior 

 end of which formed the posterior boundary of the oval interscapular foramen, the 

 anterior border of which is constituted by the posterior notch of the interclavicle 

 {i.s.f., PL VI. fig. 3 ; text-fig. 08). The posterior prolongations towards the coracoid 

 are nearly semicircular in section, the diameter of the semicircle being the sutural 

 surface by which they unite with one another ; posteriorly they join the anterior bars 

 of the coracoids by semicircular surftices which, in some cases, are further forward on 

 one side than the other, owing to the anterior prolongation of one coracoid being longer 

 than that of the other (PI. VI. fig. 3). Except for a slight prominence on its outer 

 third, the anterior border of the ventral ramus is nearly straight, and it runs inwards 

 and backwards towarrls the middle line, the anterior border of the united scapulie 

 forming a widely open V, which in life was covered by the interclavicle, which only 

 rested on the inner face of the scapulae by its outer and posterior borders, and was not 

 entirely shut in by bone below, as are the clavicles in adult specimens of Cryptocleidus ; 

 possibly, however, the V was partly closed by cartilaginous extensions of the edges of 

 the scapulae. The arrangement of the interscapular foramen has been referred to 

 above. 



