LIASSIC PTERODACTYLES. 549 



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 (6) ; it is continued 

 upwards with a convex curve, but is not pi'oduced forward like the radial ridge. 



Both ridges are connected l)y 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 ancoual depression. 



In my description of the articular end of a long-bone of a Pterosaur (figured in Pter., 

 PI. 10, 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. 9, 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 configm-ation of the distal end of the humerus in any Ptero- 

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

 feeble an indication of divisions into condyles, an absence of a general convexity, and a 

 presence of a well-defined concavity in one condyle, and as well defined a flattened or 

 feebly concave facet in the other condyle, of the distal end of a humerus." The 

 demonstration of the true characters of this end of the humerus, given in Plate 19, 

 figs. 13, 14, and d, c, have justified the refusal to regard the articular end of the bone of 

 the large Cretaceous Pterosaur as part of the humerus. 



There is no part of the skeleton of the Bird that more resembles the answerable bone 

 in a Pterosaur than the humerus. But the following, with other differences pointed out 

 in previous Sections of this work, are well marked and, as far as my observation goes, 

 constant. 



The pectoral process from the radial side of the proximal expansion of the humerus is 

 relatively longer from base to apex, with a broader, more truncate, or less pointed termi- 

 nation in the flying Reptile : it usually forms a low angle in the Bird. 



At the distal end of the humerus of the Bird the oblong radial condyle is usually 

 more pointed anteriorly ; the ulnar one is more extended transversely, and the inter- 

 condylar cleft is widened to a groove. The outer and inner ridges are not connected by 

 a post-condylar transverse ridge. The olecranial surface is more depressed, and the 

 tricipital tendinal grooves are better marked ; but the transverse expansion of the distal 

 end is less in proportion to the breadth of the shaft of the humerus in the Bird than in 

 the Pterosaur. 



Other differences in the Pterosaui'ian humerus, notwithstanding its adaptive develop- 

 ment to flight, showing departure from the avian, and approach to the crocodilian, type 

 have been previously pointed out. 



The largest vertebra in a swan, an albatross, a condor, or a lammergeyer, scarcely 



