﻿K1MMERIDGE CLAY. 



9 



cavity ' in the human ulna, the curve and depth of which surfaces is thus augmented, and 

 therewith the security of the flexible joint on which the chief movements of the bat-like 

 wing take place. The outer surface, shown in fig. 20, is of less extent, in long diameter, 

 than the inner articulation (ib., fig. 21, a ) ; a larger proportion of it is supported by the 

 olecranoid process ; and it is better defined along the margin next the longer concavity 

 (a). Nevertheless, the smoothness of the surface of the ridge, dividing the concave 

 articulations, suggests that they combined to form a single synovial hinge-joint or 

 ' ginglymus,' limiting the movements of the bones so articulated to one plane, and 

 combining freedom and extent of motion in that plane with great strength of joint. 

 The summit of the olecranoid process in the present specimen shows a rough flattened 

 surface, not a fracture, suggestive of the contact of a sesamoid, probably lodged in the 

 tendon inserted into the phalanx (ib., fig. 21 x ). 



B.—Pterodactyks Pleydellii, Owen (Plate I, figs. 15, 16, 22, 23, 23 x ). 



The portion of the fossil skeleton of the small species of Kimmeridgian Pterodactyle 

 here figured is the distal half of the left humerus. It shows the generic obliquity and 

 superiority of size of the articular convexity for the head of the radius (ib., fig. 15, a,) ; 

 that for the ulna has suffered fracture, and part of it is lost with the ulnar tuberous ridge ; 

 but sufficient remains to show its hemispheroid form, and the mere chink dividing it 

 from the radial condyle instead of the groove which is here .seen in Birds. The flexor (?) 

 ridge, leading to the broken tuberosity, extends more forward than in Pterodactylns 

 Duncani (ib., fig. 13), and contributes to a deeper concavity above the condyles on the 

 thenal aspect of the distal expansion of the humerus. The transverse ridge behind the 

 condyles is confluent therewith at its extremities, the defining groove not being developed 

 (ib. ib., 16')- The broad shallow canal for the ' triceps ' tendon marks the anconal surface 

 of this expansion (ib., fig. 16). 



To the same species of Pterodactyle may probably belong the proximal end of the 

 smaller example of the first phalanx of the fourth or wing-finger, of which I have given two 

 views in Plate I, figs. 22, 23, and 23 x , to contrast with those of the same bone and part 

 of Pterodactylus Manselii. The olecranon process in Pterodactyl us PleydelRi is relatively 

 longer and more incurved; its apex is not truncate; it is more compressed; has a 

 smaller and lower posterior tuberosity, and a smaller basal tuberosity. The longer 

 concave articulation is similarly extended upon the anterior angle. From the tuberosity 

 at the corresponding or lower end of the shorter concavity a ridge is continued down 

 the bone, giving a triedral form to the shaft as far as it is preserved in this and the 

 previously described specimen (figs. 20, 21). The bony wall of the shaft is thin and 

 compact, the air-cavity large, and in one specimen occupied by crystallised calcite. 



b 



