632 ME. G. A. BOULENGEK ON SOlILUaKL's GAVIAL. [JuilO 10, 



Cuvier (Ossein. Foss.) describes and figures the second rib in 

 Crocodilus porosus as single-headed and attached to the odontoid 

 bone. Owen (Osteol. Cat. Mus. Coll. Surg.) ascribes to the same 

 rib, in Gavialis gangeticus, a forked head attached to two transverse 

 processes of the odontoid bone. According to Staunius (Zoot. 

 Araph. p. 26), the rib is forked and the two brandies are attached 

 on the limit between the odontoid bone and the centrum of the 

 axis. Briihl (Skel. Orocod.) figures, in Oaiman palpebrosus, the rib 

 as forked, with capitulum and tuberculum on the odontoid bone, 

 near its suture with the axis. In Huxley's 'Anatomy of Ver- 

 tebrated Animals ' it is described in Crocodilians generally as 

 attached to the os odontoideum and to the second centruui by 

 distinct capitular and tubercular processes. Baur (Amer. Nat. 

 1886, p. 228) was the first in attempting to show what, if any, 

 differences exist between the genera with regard to the shape of 

 the second rib and its attachment to the vertebrae. I am not able 

 to confirm his statements regai'diug Gavialis and Alligator. In 

 the case of the latter, the more forward position assigned by him 

 to the costal capitulum may be due to individual variation ; but I 

 cannot help thinking the author is mistaken in attributing a rudi- 

 mentary diapophysis to the neural arch of Gavialis. In the 

 specimens I have examined two very distinct processes are present 

 on the axis-centrum, and I have satisfied myself on a specimen in 

 spirit that the ligamentous capitulum is attached to the upper of 

 these processes, which . is widely separated from the supposed 

 diapophysis figured by Dr. Baur. 



I have examined the atlas and axis in Gavialis yangeticus, 

 Tomistoma schlegeli, Crocodili niloticus, americanus, and porosus, 

 Osteolcemus tetraspis, Alligator mississvppiensis, Oaiman sclerops and 

 G. latirostris, and find important diflierences, which are deserving 

 of notice. 



In Alligator, the first rib is attached to the lower surface of the 

 hypapophysis and in contact with, or narrowly separated from, its 

 fellow at the base ; the second rib, in the adult, is deeply forked and 

 attached by its capitulum to the centrum of the atlas, by its tuber- 

 culum to the anterior part of the centrum of the axis, which, 

 however, does not develop any tubercle or transverse process. In 

 a new-born specimen I find both capitulum and tuberculum 

 inserted on the axis, showing the rib to shift forward with age, a 

 further confirmation of the view that this rib, usually attached to 

 the first vertebra, really pertains to the second. 



In Caiman, the first I'ib is as in the preceding, but the second, 

 deeply forked, is entirely on the centrum of the atlas, without the 

 latter bearing processes for its attachment. 



In Crocodilus, the first rib is more on the side of the hypapo- 

 physis and widely separated from its fellow ; the second is but 

 feebly notched in its proximal portion, and the somewhat ill-defined 

 capitulum and tuberculum join two strong knob-like processes on 

 the centrum of the atlas. 



In Gavialis, the first rib conforms to the preceding type, but 



