ON THE OSTEOLOGY OF NYCTOSAURUS. 131 
sible to say whether the odontoid appears on the floor of the neural 
canal or not. 
The axial intercentrum is a large, wedge-shaped piece intervening © 
between the atlantal intercentrum and the body of the axis. It is scarcely 
keeled in the middle below and reaches as high on the sides as does the 
atlantal intercentrum. 
The body of the axis is short and much expanded posteriorly. Its 
ball is small and widened transversely. Below the ball the body is 
expanded into a very large, flaring rim, inclosing a deep concavity, 
having a broad articular surface transversely. ‘This surface evidently 
corresponds to the united postexapophyses of the later vertebrae—the 
“posterior parapophyses”’ of Owen and Plieninger. Nothing quite simi- 
lar to this structure seems to have been observed in any of the European 
pterodactyls, though an axis figured by Owen,* as also Seeley, seems to 
approach this structure. Nor do I find a corresponding adaptation of 
structure in any of the following vertebre. 
The arch of the axis is broad and relatively high. The neural rim in 
front, to which are applied the dorsal neurapophyses of the atlas, is thin, 
forming a heart-shaped opening. The spine is broad, low in front, where 
there is a thin margin, for a short distance, and is highest behind. The 
sloping border is thickened, the posterior border thin. Below, on each 
side, there projects backward a strong process, on the under side of which, 
before its termination, is the small, oval zygapophysis. 
In the figures given in P]. XLI, I have partially restored the axis and 
atlas after two specimens, both complete, but compressed in different 
ways. The length of the atlanto- axis is 14 nm. 
Plieningery describes the atlas in Prerodactylus kochit as consisting of 
a “‘ziemlich massiven K6rper, sowie aus einem Nervenrohr umschlies- 
senden Bogenpaar, welches aussen und oben jederseits einen Fortsatz 
tragt, der wohl zur Anheftung von Muskeln diente.”’ He also identifies 
the bone considered by Fraasf{ as a “‘Schlundring”’ as the atlas. From 
the description and figure it would seem that the atlas of Prerodactylus 
is of a very different structure from that in Vyctosaurus and Pteranodon. 
(I have seen the united axis and atlas in a species of the latter genus; 
they resemble the same bones in JVyctosaurus.) 
Third—seventh cervical vertebre, Pl. XLIII, Figs. 7-8. The cervical 
vertebrz were lying close together between the back of the skull and the 
top of the thorax, but they were dislocated and disassociated, so that 
nothing can be told of their sequence from their position. Three are 
* Brit. Fos. Rept. iv. Pl. viii, fig. 2. 
~ Paleontographica, 1901, p. 17. 
t Paleontographica, xxv, Pl. xxii g 
