﻿58 



FOSSIL REPTILIA OF THE 



preceding Monograph, 1 its base has a minor relative extent than in Omosaurus ; the shaft 

 beyond that ridge expands more gradually into the distal end ; the entire length of the 

 bone — 4 feet 4 inches in Cetiosaurus longus — is greater in proportion to the breadth or 

 thickness of the shaft. 



The more slender character of the humerus is still more marked in that bone which 

 chiefly represents Mantell's genus Pelorosaurus (Pal. vol. for 1857, Tab. XII), in 

 which the radial or pectoral crest (ib., fig. 2, d) subsides above the middle of the shaft, 

 encroaching, as in the Crocodile, Varanus, and Pterodactyle, upon the palmar surface of 

 the bone. 



The humerus of Iguanodon is still less robust in proportion to its length, not to 

 mention its inferior size as compared with associated dorsal vertebra?, than in Omosaurus. 



In Hylaosaurus we find the nearest approach to Omosaurus in the proportion of the 

 length of the humerus giving attachment to the great tuberous crests from the radial and 

 ulnar sides of its proximal part. But in the Isle of Wight specimens referred, with doubt, 

 to that Dinosaur, the radial crest is more strongly, and, in reference to its Saurian nature, 

 more typically twisted palmad than in the huger Kimmericlgian genus. It shows a 

 tuberous thickening anconad of its distal end, in the place of the ridge, d', fig- 2, 

 PI. XVII, in Omosaurus." 



§ 8. Radius. — This antebrachial bone in Omosaurus (PI. XVII, figs. 7 — 11) has a 

 subcompressed shaft, expanding moderately and almost equally into the two articular ends, 

 as far as their degree of conservation shows ; but it is probable that the more mutilated 

 distal end (fig. 10) when entire would give a somewhat greater breadth than the proximal 

 one or ' head.' This (ib., fig. 9) is of a narrow subelliptic shape. A small part of the 

 concave articular surface, a, for the radial condyle of the humerus, is preserved. The 

 anconal surface of the shaft (fig. 7) is feebly divided at its distal two thirds into two 

 facets by a low rising, hardly to be called a ridge, beginning at the middle of that 

 surface at its proximal third and inclining as it descends toward the radial border of 

 the distal end. The concavity of both borders, and especially of the ulnar one, narrows 

 transversely the shaft, but this preserves more equably its ancono-palmar thickness (see 

 the section of the middle of the shaft in fig. 11). The lateral facet (fig. 8, 6) at the 

 proximal end for articulation with the ulna is more convex than is usual in Beptilia. 



The surface (ib., fig. 8, e) for the insertion of the biceps tendon is well defined. The 

 thenal prominence (ib., figs. 8 and 10, /) extending or deepening the cup, y, for the 

 scaphoid, is strongly developed, and is thicker than usual, as far as it is preserved. Its 

 outer surface is roughened, as if for the ligamentous attachment of some bone, such sur- 

 face extending to the angle, U (fig. 8), at the broadest part of the distal end of the radius. 



1 On the genus Cetiosaurus, p. 31, fig. 3. 



2 Compare Plate XVII, figs. 1 and 2, with similar figures of the humerus of HylcEosaurusI given 

 by Mr. Hulke, in the ' Quarterly Journal of Geological Society,' vol. xxx, pi. xxxi (1874). 



