OF THE EYE. 67 



trils of sea-serpents ; but in the Homalopsis, some liave 

 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 vnth 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 

 tliis 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 

 mth 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. chi Mus., vii. p. 62. See also Mullek, and Tiedemanx, 

 Zeitsckr. iv. p. 19, fig. 15. 



