CRETACEOUS PTERODACTYLES. 385 



VertehrcE of Pterodadylus. PI. 7, figs. 11 — 14. PI. 8. 



The most instructive specimens from the Cambridge Green-sand are those which 

 have afforded the precise and hitherto unknown characters of certain vertebrae of 

 Pterodactyhs. Viewed as indicative of the generic character of these bones, they 

 give the earliest known example of the " procoelian" type of vertebrae in the Reptilian 

 class, being the first cujj-and-ball vertebrae, with the "cup" at the fore part of the 

 centrum, met with in the ascending order of strata. It cannot be doubted that this 

 structure prevails in the moveable vertebree of the neck and back of all Pterosauria, 

 and must be predicated of the Dimorphodon* of the Lias as well as of the Pterodactyhs 

 of the Green-sand, in which the structure is now clearly demonstrated. The chief 

 difference which the Pterodactyle presents in this respect from modern Lizards is, 

 that both the cup and ball are of a more transversely extended elliptical shape in 

 most of the vertebrae of the flying Saurian. 



Amongst the numerous vertebrae submitted to me were specimens of united, or 

 partly united. " atlas and axis." 



The atlas consists of a centrum (PI. 7, figs. 11 and 12, c), of two slender 

 styliform neurapophyses (ib.^ n), and of a very small discoid neural spine. The centrum 

 is so short as to be discoid ; it is flat where it joins and becomes anchylosed to the 

 axis {ex, x) , and is concave for the occipital tubercle : this cup (PI. &, figa. 1 and 5, c) 

 is circular ; its depth is shown in the section of the anchylosed atlas and axis, PI. 7, 

 fig. 12. The neurapophyses (n), resting on each side of the upper half of the centrum 

 of the atlas, converge and articulate above with two small tubercles, as shown in fig. 13, 

 on the fore part of the neural arch of the axis ; the neurapophyses almost meet, but do 

 not unite above the neural canal. 



The body of the axis is eight times longer than that of the atlas ; it expands 

 posteriorly, and terminates by a transversely elliptical ball (6) at the upper part of that 

 end, and in a pair of thick, short, obtuse, diverging apophyses {p), at the lower part. 

 There is a rudimental hypapophysial ridge, fig. 1 2, //, from the middle and toward the 

 fore part of the under surface of the centrum ; the extent to which this surface 

 descends below the hinder ball, and between the apophyses (p), is shown at PI. 7, 

 fig. 12, X. 



The centrum of the axis vertebra is confluent with the neural arch, fig. 1 1 , n, j^ ; at 

 the middle of the side, apparently crossing the line of junction, is a large subcircular 

 aperture, which leads directly into the widely cancellous structure of the bone, below the 

 neural canal. This vacuity (fig. 11, o) answers to the " foramen pneumaticum" in the 



* ' Reports of the British Association,' 18."*8. 



