632 MR. G. A. BOULENGER ON SCHLEGEL’S GAVIAL. [June 16, 
Cuvier (Ossem. 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 Stannius (Zoot. 
Amph. p. 26), the rib is forked and the two branches are attached 
on the limit between the odontoid bone and the centrum of the 
axis. Briihl (Skel. Crocod.) figures, in Caiman 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 centrum 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 vertebra. I am not able 
to confirm his statements regarding 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 Gavials gangeticus, 
Tomistoma schlegeli, Crocodili niloticus, americanus, and porosus, 
Osteolemus tetraspis, Alligator mississippiensis, Caiman sclerops and 
C. latirostris, and find important differences, 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 rib 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 
