CRETACEOUS FORMATIONS. 9 



bird is convex transversely, but concave vertically, not simply convex, as in tbe 

 Pterodactyle ; thus a portion of the vertebra of that reptile, notwithstanding its 

 pneumatic structure, might be distinguished from the vertebra of a bird. 



In the ordinary neck-vertebras of the Pterodactyle the centrum is oblong, subde- 

 pressed, slightly compressed at the middle, subcarinate (Tab. II, figs. 11, 12, h), 

 or with a low obtuse hypapophysis (fig. 18) at the fore part of the under surface, 

 which expands laterally to join the base of the anterior zygapophyses (ib. a). The 

 back part of the centrum expands and bifurcates into the short, thick, obtuse 

 parapophyses (figs. 11 and 18, b), the anterior concavity (fig. 10, c) is a long transverse 

 oval, with the upper border somewhat produced : the hinder ball (fig. 8) has a similar 

 transversely extending elliptical figure, directed a little upwards ; it appears to be 

 tilted up by the curve of the under surface of the centrum, above the level of the 

 terminal tuberous parapophyses (p). A large pneumatic foramen (figs. 7, 13, 15, o) 

 of an elliptic form, opens upon the middle of each side of the centrum, close to 

 the anchylosed base of the neurapophysis. The texture of the centrum (fig. 19) 

 presents a few very large cancelli, which communicated by the pneumatic foramen with 

 the cervical air-cells. The smooth outer wall of the centrum is a very thin but compact 

 plate of bone : it becomes a little thicker where it forms the articular cup and ball. 



The neural arch, between the notches of the nerve-outlets, is not quite two 

 thirds the length of the centrum. The hinder notch is the deepest ; the arch is low, 

 broad exteriorly, less concave on each side than it is before and behind (Tab. II, 

 fig. 17), with the four angles somewhat produced, and supporting the articular surfaces, 

 of which the two anterior (fig. 18, a) look upward and inward, the two posterior (fig. 

 16, z) downward and backward. The sides of the neural arch extend outward so as to 

 overhang those of the centrum (fig. 18). The posterior zygapophyses (z), do not 

 extend so far back as the articular ball of the centrum. 



Figs. 7 to 1 1 give five views of the natural size of a middle cervical vertebra, 

 which, according to the proportions of Pterodactylus suevicus, Qnstd.,* may have 

 belonged to a Pterodactyle with a first phalanx of the wing-finger of about one foot in 

 length. In fig. 12 the under surface of the centrum is well preserved; it differs 

 from that of the larger cervical vertebra (figs. 7 — 11) in being flatter from side to 

 side, and in being concave instead of convex from before backward ; the concave 

 contour being due to the median production, gradually extending into the obtuse 

 hypapophysis (h) at the fore part. This difference indicates that the present vertebra 

 had a more advanced position in the cervical series than fig. 7, which may probably 

 have been the sixth. The superior breadth of the neural arch over the centrum is 

 well shown in fig. 12 ; and the relative positions of the zygapophysis (z), the articular 

 ball (&), and the parapophysis (p), at the hinder end of the vertebra, are seen in 

 fig. 13, which is a side view of the same vertebra. 



* Quenstedt, ' Ueber Pterodactylus suevicus,' 4to, 1855. 



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