﻿LIASSIC FORMATIONS. 



13 



of this part of the bone is less than that of the contracted cylindrical part of the shaft 

 lower down, the section of which is circular. 



This humerus, besides being smaller than that of Dimorphodon macronyx* has a more 

 straight and slender shaft, which in transverse section is more nearly cylindrical. 



B. — Dimorphodon Macronyx, Owen (Plate I, figs. 13, 14). 



The other Pterosaurian fossil, obtained by Mr. Marder, from the same formation and 

 locality, might well, by its superior size, and more ellipsoid section of the shaft, have 

 formed part of the first long-bone of the wing of the species restored in the ' Monograph 

 of Liassic Pterosauria' of 1S70. 



The articular surfaces of the humerus in both specimens of this Pterosaurian figured 

 in that Monograph (Mon. cit., Plates XVII, XVIII, 53, 53 1 ) were too much crushed and 

 mutilated for profitable description. The present specimen shows instructively the distal 

 articulation. 



The surface for the radius presents one uniform convexity, a, oblong in shape, and 

 obliquely disposed, extending from the lower part of the radial riclge (c), upward, forward, 

 and ulnad; it is almost wholly developed from the thenal aspect (fig. 13), only the lower 

 border of the convexity being visible from the anconal side (at a, fig. 14). It is longer 

 and more prominent than the ulnar convexity or condyle. This (ib., b) is subhemispherical ; 

 its diameter equals the shorter diameter of the radial condyle. The intercondylar fissure 

 is a mere cleft; and tuberous ridges, extending from the condyles, augment the breadth of 

 the distal end of the humerus. The outer or radial one (c) is produced forward, 

 bounding there, and in part forming the anterior concavity. The inner or ulnar ridge 

 (d) is more distally placed, projecting to a lower level than the condyle (i) ; it is continued 

 upwards with a convex curve, but is not produced forward like the radial ridge. 



Both ridges are connected by a narrower one, extending transversely behind the two 

 condyles, from which it is divided by a fossa (fig. d, c). There is a broad and shallow 

 depression on the back part of the distal end of the humerus for a large " triceps " tendon : 

 there is no anconal depression. 



In my description of the articular end of a long-bone of a Pterosaur in the Supplement, 

 No. 1, to the 'Monograph on Cretaceous Pterosauria " (1857), p. 16, Plate IV, figs. 1, 

 2, 3, I remarked that, " guided by considerations of size, the fragment might form the 

 opposite end of the bone, indicated by the articular ends (PI. II, figs. 7 and 8), which 

 were referred to the head of the humerus. But I proceeded to remark, « I am not 

 acquainted with the precise configuration of the distal end of the humerus in any Ptero- 

 dactyle. Prom general analogy, however, one should scarcely be prepared to find so 



1 « Monograph of Liassic Pterosauria,' Pal. vol. for year 1869, pi. xviii, figs. 53, 53 a. 



