1886.1 Zoölogy. 289 
mississippiensis the bones are separate but not elongated as in 
Jacare. Usually the two elements unite early in the embryo. 
It is possible that a proatlas existed in Rhynchosaurus 
Owen, a reptile very nearly allied to Sphenodon (Hatteria). 
Sphenodon has rudiments of the proatlas, as shown by Albrecht;* 
therefore the same bones ought to be present in Rhynchosau- 
rus; this seems to be confirmed by a note by Owen? on this 
rept tile. 
“ A small flattened triangular plate, which adhered to the pos- 
terior part of the skull, was suspected by Dr. Ward to be a tooth; 
it appeared to me, from the character of the exposed surface, to 
have at least equal claims to be regarded a dermal scute. In pre- 
paring the mold of the cranium this part was detached and lost, a 
circumstance which I have much regretted, since it prevented my 
applying to it the test of a microscopical examination 
In his detailed ape ue of Rhynchosaurus, eee, does not 
mention this poin 
I believe it oni that the small flattened TAREA plate, 
“which adhered to the posterior part of the skull,” represents a 
piece of the proatlas. 
It is probable that the proatlas is present also in the Proto-. 
rosauria, which have many characters common with Sphenodon. 
Il. Atlas and Axis—The centrum of the atlas is always repre- 
sented by the odontoid process of the axis, and can be separated | 
easily in the Crocodilia. The piece below the centrum of the 
atlas, supportin g the neural arch of that vertebra, is the Oe 
pophysis, between the proatlas and the atlas 
The hy papophysis between the atlas and axis is probably co- 
ossified with the anterior and lower part of theaxis-centrum, asin 
irds and some dinosaurs. There seems to be a great confusion 
in the determination of the ribs belonging to the first vertebra 
in the Crocodilia, and’even about the true nature of these verte- 
bre. Koken’ says, 1882: “ Es ist erstaunlich und befremdend, _ 
wie sehr bei diesen sonst so conservativen Thieren die Ausbildung 
der ersten Halswirbel, und zwar in wesentlichen Punkten, differirt. 
Vorlaufig erscheint es unmöglich, in Art und Reihenfolge il 8 
Ve eraenderungen eine Cie zu bringen.” A 
his is very s indeed. We find it very much more 
“ befremdend,” sasa Eoia says (p. 808), that an aligator (4. : 
t, P. Note sur la présence ae rudiment de proatlas sur un exalt 
de Haters, unciata Gray. Bull. Mas. Roy. Hist, Nat. Belg, T. 1t, 1583, p. 190- 
; Stag R. Report Brit. Fossils, Rept. k: Brit. Assoc. Rep., 1841, p- 150. — 
en, Description of an extinet lacertilian Aag (Riper aie 
Omen) of which the bones and footprints characterize the upper n Red : 
S 
will, near Shrewsbury. Cambr. Philos. Soc. Trans., Vit, 1842, pP- sc 
5 mene E: -Dié Reptilien der norddeutschen unteren Kreide. Z 
Deutsch. Geol. Gessellsch’ Jahrg, 1 1883, p. 808. ie 
