OF THE EYE. 
67 
trils of sea-serpents ; but in the Homalopsis, some have 
them a transverse fissure in the form of a crescent. 
We find in the Trigonocephalus and the Crotalus, on 
the sides of the snout, behind the nostrils, a large cavity, 
of which the use is unknown, but we may consider it, ac- 
cording to all appearances, as an accessory to the nose. 
This cavity, scooped out in the upper surface of the maxil- 
lary bone, is lined with a species of mucous membrane ; 
it has small holes for the passage of nerves, and probably 
receives a portion of the fluid secreted by the adjacent 
glands. Home,^ who has treated of this subject in a 
special memoir, supposes these cavities to be analogous to 
the lachrymal fossa of certain Ruminants. 
OF THE EYE. 
We have mentioned already the diversity in the position 
of the eye in the different races of Ophidians, of the nature 
of that organ, of the form of the pupil, &c. ; we have also 
stated that the exterior integuments cover the whole 
eye, but that these integuments are extremely thin over 
this organ, diaphanous, presenting the form of a hemi- 
spherical lamella, adherent to the plates which form the 
orbit. It is obvious that this lamella, as an integrant part 
of the skin, is renewed at the time of casting the skin, and 
that the old one is thrown off with the epidermis. The 
globe of the eye is generally orbicular, and is covered an- 
teriorly by the conjunctiva, which, doubling on itself, forms 
a cavity, into which the tears are poured, according to the 
observations of Cloquet. t The cornea is very thick, and 
presents a segment of nearly the same sphere as the sclerotic; 
this last tunic, equally thick, and very tough, is not sup- 
ported by any bone or cartilage. Its two surfaces are tinged 
with a deep brown colour. We find at the bottom of the 
orbit an orbicular hole for the passage of the optic nerve^ 
which perforates obliquely the sclerotic coat. On its ex- 
ternal surface, the muscles of the eye, generally six in 
^ See Russel’s Appendix. 
t Mem. du Mus., vii. p. 62, See also Muller,, and TiedemanN;^ 
Zeitschr. iv. p. 19, fig. 15. 
