14 FOSSIL REPTILIA OF THE 



scapula extends upward and backward, as a slightly bent sabre-shaped plate, a little 

 twisted on itself. The coracoid is thicker, straighter, and shorter than the scapula ; 

 it is rather suddenly expanded at the sternal end, where it is most compressed : 

 the scapular end developes a protuberance below the glenoid cavity. 



The scapular arch in Pterodactylus giganteus, Bwk., from the Chalk of Kent 

 ('Monog. Cretaceous Reptiles,' 1851, p. 93, Tab. XXXI, fig. 7), was distinguished 

 by a tuberous (acromial) process from the scapula, near the glenoid cavity, the corre- 

 sponding anterior process from the coracoid being well marked. 



The fossil fragment from the Cambridge Green-sand (Tab. Ill, figs. 1 and 2) 

 consists of the coalesced extremities of the scapula (a) and coracoid (&), where they form 

 the glenoid cavity for the humerus. The margins of the cavity are in part abraded, 

 but its long diameter cannot have been less than 1 inch 3 lines ; it is concave 

 vertically, rather convex transversely below, but plane, or a little concave, in that 

 direction at the upper or scapular end. The cavity is transversed obliquely by a 

 depression pretty equally dividing it, and indicating the respective shares of the 

 scapula and coracoid in its formation prior to the anchylosis of those two bones. 

 The end of the scapula, near the cavity, would present an unequally three-sided figure 

 in transverse section, the side looking inward and that looking forward being 

 concave, the side looking outward convex. Half an inch above the border of the 

 glenoid cavity is the fractured base of the (acromial) process answering to that in 

 Pterodactylus giganteus, but which is more feebly developed in Pterodactylus 

 macronyx, Bkd., and Pterodactylus suevicus, Qnstd. Beyond this process the bone 

 rapidly contracts in size, and presents an oval transverse section, as at a, fig. 2, 

 Tab. HI. 



The surface of the coalesced extremities of the bones which is applied to the 

 thorax is concave in every direction, and an inch in breadth, with a long narrow 

 (pneumatic) aperture near its hinder border. The anterior production of the coracoid 

 has been broken away at c (figs. 1 and 2), the coracoid quickly contracts as it recedes 

 from the humeral articulation to a size and shape shown by the section b (fig. 2). 

 The size of the entire scapular arch, according to that of Pterodactylus macronyx, is 

 shown by the dotted outlines in fig. 1 . 



Fig. 3 shows the articular surface of the scapular arch of a Pterodactyle of larger 

 size than the preceding specimen ; the oblique groove indicative of the portions con- 

 tributed by the scapula and coracoid to the cavity is well marked, as it also is in the 

 corresponding fragment of the scapular arch of the smaller Pterodactyle (fig. 4). In 

 the still smaller but similar fragment of the scapular arch (fig. 5), the posterior 

 concave surface shows the long (pneumatic ?) foramen very distinctly, and also a 

 trace of the primitive separation of the scapula and coracoid. If this specimen has 

 belonged to a young individual of either of the two larger species, it shows that the 

 union of the two bones takes place at an early age. In the bird, although the early 



