178 MAEINE EEPTILES OF THE OXFOED CLAY. 



ventral ramus, forms a nearly rectangular surface about 7-8 cm. long and 5 cm. deep ; 

 its antero-dorsal angle is rounded, while its antero-ventral angle is prolonged forwards 

 as the inner edge of the thin anterior region of the scapula. The symphysial surface 

 is deeply pitted and grooved by channels, which seem to have communicated with the 

 exterior by a foramen situated on the upper surface at the middle of the symphysis. 

 The outer surface of the ventral ramus of the scapula is nearly flat, but the visceral 

 (upper) surface is divided into the raised and thickened symphysial region behind and 

 the thin depressed anterior area which supports the clavicle, the two being separated 

 by the ridge against which the hinder edge of the clavicle rests. In this thin anterior 

 region the two scapula; do not actually meet in the median line, but are separated by a 

 narrow V-shaped interval, covered by the inner borders of the overlying clavicles ; it is 

 possible that this interval was filled by cartilage and that in advanced age the scapular 

 symphysis was prolonged to the extreme anterior end. 



The clavicles (cl., PL X. figs. 1, 2 ; text-figs. 87-89) are in the form of scalene 

 triangles. The outer and posterior borders meet in an acute angle and the posterior 

 border is sometimes concave. The lower surface of the outer angle bears a roughened 

 facet (s.sc), which fits against a corresponding rugosity on the anterior edge of the 

 scapula and no doubt united closely with it. This union of the outer ends of the 

 clavicles with the anterior borders of the scapulce is a point of considerable interest, 

 since it is probably a remnant of the original condition seen in the Nothosauridse (text- 

 fig. 61 B, p. lOS), in which the clavicular arch stretches from one scapula to the other, 

 the ventral plates of these bones being still widely separated, as, indeed, they are in the 

 young shoulder-girdle of Cryptocleidus (see below). The outer border is nearly straight 

 and is thin and sharp, and is usually turned a little downwards so as to fit closely 

 agninst the anterior edge of the scapula. The inner (median) borders {sym.) of the 

 clavicles are thickened and meet in the middle line at least in the anterior third. 

 Behind this there is a notch on each clavicle, which in a former paper was described as 

 showing either that a blood-vessel passed between the two bones at this point or that a 

 rudimentary interclavicle was present. The latter explanation seems to be the correct 

 one, though it is by no means sure that this element always ossified. In the specimen 

 figured on PL X. fig. 2 the notch is well developed, but the clavicles behind it seem to 

 have met in the middle line, so that the interclavicle, if present at all, must have been 

 very small. In the specimen shown in text-fig. 8S, on the other hand, there is a distinct 

 interclavicle, the anterior slightly forked end of which fits into the notches in the 

 clavicles, while its thin posterior prolongation lies between them in the middle line for 

 the posterior two-thirds of their length. The occurrence of this rudimentary interclavicle 

 in Crypfocleidiis, like the existence of rudimentary clavicles in Mureenosaurus, shows 

 tbatboth these genera were probably derived from some form in which, as in Tricleidus, 

 both clavicles and interclavicles were well developed. 



The coracoids {cor., PL X. fig. 1 ; text-figs. 87-89) are very large, and, so far as concerns 



