﻿CRETACEOUS FORMATIONS. 



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The rich repository of remains of gigantic Pterosauria in the Upper Green- 

 sands of Cambridgeshire have added valuable evidence on these important points, 

 and demonstrate a nearer approach to the keeled character of the breast-bone of 

 flying birds than the specimens of the smaller species described in the under- 

 cited works appear to demonstrate. By the kindness of Professor Sedgwick, 1 

 am enabled to compare the specimens of portions of the sternum acquired by the 

 Woodwardian Museum with that which has recently been purchased by the 

 British Museum. The best of these specimens consist of little more than the 

 thicker and stronger, contracted forepart of the breast-bone (Tab. II, figs. 7, 8, 

 and 9), broken away from the thin, expanded, fragile plate (h), of which it princi- 

 pally consists, and of which remains or impressions have been preserved in a few 

 slabs of fine-grained stone of the Oolitic series, such as the lithographic slate ; 

 that of Pterodactylus suevicus * showing the posterior border of the symme- 

 trical plate to be convex and entire, not notched or perforated, as in many birds. 

 The forepart of the sternum of the gigantic Pterodactyle from the Cambridge 

 Green-sand includes the major part of the anterior process, and also the pair of 

 articular facets for the coracoids. The keel-like process in the specimen 

 (Tab. II, figs. 7, 8, 9, b, <?,/) is continued forward from that articular region (d, c) } for 

 an extent equal to the depth of the bone at the same part ; but the process is not 

 entire. Its base is gently convex at the sides, from the middle and thickest part 

 of which it gradually narrows to a ridge, of about a line or less in thickness at 

 both the upper and under margins ; the extreme forepart being broken away, 

 prevents the determination of the precise extent or contour of that end, but 

 the convergence of the preserved parts of the upper and under margins 

 indicate a convexly rounded termination (fig. 7, <?). There is a gentle de- 

 pression on each side of the beginning of the upper part of the ridge, which ridge 

 is continued from a thickening or tubercle (figs. 7, 8, b), bounding anteriorly a 

 small, deep, transversely oval depression (d) between the two articular surfaces 

 for the coracoids (c). This tubercle answers to what I have termed the " manubrial 

 process" in the sternum of birds,f and the above pre-coracoid part of the 

 sternum answers to that process, confluent below, as in Aptenodytes, with the 

 produced " keel." This, however, in Pterodactylus, quickly loses depth as it 

 extends backwards along the mid-line of the under part of the sternum, some way 

 behind the articular region, and has not quite subsided at the forepart of the 

 expanded body of the breast-bone (fig. 9,/), from which the rest of the shield-like 

 plate has been broken away. The sides of the post-coracoid part of the keel are 

 gently concave ; the lower border of the keel is first convex, then concave to near 

 its posterior termination, both in a very feeble degree (fig. 7, e ,f). Each of the 



* Quenstedt, 'Ueber Pterodactylus suevicus, im Lithograpliischen Schiefer Wiirtembergs,' 4 to, 1855. 

 t Art. "Aves," ' Cyclopaedia of Anatomy and Physiology,' vol. i, 1836, p. 282, fig. 129. 



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