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 vertebras. 



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 PI. 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 mm. 



Plieningerf* describes the atlas in Pterodactylus kochii as consisting of 

 a "ziemlich massiven Korper, 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 FraasJ as a " Schlundring " as the atlas. From 

 the description and figure it would seem that the atlas of Pterodactylus 

 is of a very different structure from that in Nyctosaurus and Pteranodon. 

 (I have seen the united axis and atlas in a species of the latter genus; 

 they resemble the same bones in Nyctosaurus.} 



Third — seventh cervical vertebra, PI. XLIII, Figs. 7-8. The cervical 

 vertebra; 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. PI. viii, fig. 2. 

 tPaleontographica, igoi, p. 17. 

 % Paleontographica, xxv, PI. xxii g 



