CRETACEOUS FORMATIONS. 17 



one, which we may call the anterior (d), is convex and of small extent, and behind it 

 is a well-defined part of a concave surface (b). At the fore (?) part of the bone 

 (fig. 2) the two convex surfaces extend a little upon the shaft (a), and are divided 

 from each other by a moderate median depression ; where the thin smooth outer crust 

 of bone has been worn away, the small superficial cancelli are exposed. At the back(?j 

 part (fig. 3), where the major part of the bone is broken away, the larger cancelli 

 are exposed. 



Guided by considerations of size, the fragment (Tab. IV, figs. 1 — 3) might 

 form the opposite end of the bone indicated by the articular ends (Tab. Ill, figs. 7, 

 and 8). I am not acquainted with the precise configuration of the distal end of the 

 humerus, in any Pterodactyle ; indeed, the articular surfaces of very few of the bones 

 of this remarkable reptile have been perfectly preserved, so as to be recognisably 

 delineated and described. From general analogy, however, one should scarcely be 

 prepared to find so feeble an indication of divisions into condyles, an absence of 

 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 form of articulation above described would seem rather to be that 

 of the end of an antibrachial bone adapted to join the bones of a carpus. But, on 

 the hypothesis of the fragment in question being either proximal or distal, and of a 

 radius or ulna, it expands our ideas of the bulk of the Green- sand Pterodactyle even 

 beyond those suggested by the manifestly head of the humerus (Tab. Ill, fig. 7). 

 The present description and figures will at least help, it is hoped, to forward a precise 

 knowledge of the osteological characters of the Pterosaurians. 



Assuming that we have in figs. 1 — 3, Tab. IV, the articular end of an 

 antibrachial bone, then, according to the proportion which the broadest end of one 

 of these bones bears to its total length in the Pterodactylus suevicus, the length of 

 such antibrachial bone in the great Pterodactyle of the Green-sand here indicated 

 would be 16 inches. The total length of wing will be calculated on this basis at the 

 conclusion of the present Monograph. 



The fifth or wing-metacarpal. 



The trochlear joint of the bone (Tab. IV, figs. 9 — 11) belongs to the distal end of 

 the metacarpal of the fifth or wing-finger. The pulley is more complex, in the large 

 Pterodactyles here described, than it is in similar trochlear joints of other animals ; 

 there are three convex ridges, a, b, c, which traverse the articular surface from behind 

 forward, describing rather more than half a circle ; the middle ridge, c, is less prominent, 

 and of less extent than the lateral ones which form the sides of the pulley. The direc- 

 tion of the ridges is rather oblique, and one which, to help the description, may be called 



3 



