222 THE BATH OOLITE PERIOD. CHAP. 



The side profile of the jaw shews nearly parallel boundaries, the 

 whole formed on a curve, convex upward behind, convex downward 

 in front. There is no elevated coronoid process, and only a gentle 

 rising in front of the articulation. The two rami are anchylosed 

 together in Lord Ducie's specimen, in other cases they have been 

 separated. In the cross section the outer margin is raised higher 

 than the inner. In these particulars it somewhat resembles plesio- 

 saurus. The composition of the jaw is not clearly traceable, owing 

 to ossification. 



Length of the specimen in Mr. Quekettfs collection 4-75 inches, 

 greatest depth 0*5. Judging by the specimens of Dimorphodon 

 macronyx, this should give the cranium and upper jaw a length 

 of fully five inches; which is much less than the corresponding 

 measure in dimorphodon, whose wing-bones are only two-thirds 

 as long as those of rhamphorhynchus. Rhamphorhynchus thus 

 appears to have had very different proportions from those of di- 

 morphodon a smaller head and longer wings. 



Diagram LXXII. Vertebrae of Rhamphorhynchus. Scale one-fifth of nature. 



The cervical vertebrae of the Stonesfield fossil are not completely 

 cleared in our specimens : their length is 0*75 inch ; so that 

 allowing for the small atlas and cartilage, we should have somewhat 

 about five inches for the cervical region, which agrees with the 

 measure of dimorphodon. 



We come now to the shoulder girdle, of which we know only 

 the scapula and coracoid represented in Diagram LXXIII. These 

 are almost identical with the parts bearing the same name in 

 dimorphodon. 



The scapula is a long, narrow, arched plate, thin and sharp-edged 

 in the upper or free part, growing thicker toward the point of 

 union with the coracoid. This union is by synostosis ; at least 

 three specimens agree in having the bones united, though in 

 two others they are separated. Length of the largest, three 

 inches. 



