EYE AXD EYELID OF SERPENTS. 387 



The eye of Serpents is protected by an eyelid of a very remarkable character ; for that it is an 

 eyelid, and not, as is very generally supposed, the cornea, its anatomical relations abundantly prove. 

 It consists of a transparent membranous expansion, which is immovably fixed in a kind of frame 

 formed for its reception by a circle of scales, usually seven or eight in number, disposed around the 

 margin of the orbit. This eyelid is formed of three superposed layers. First, an epidermic layer 

 which is elastic and pretty thick where it covers the middle of the eye, but towards the circumference 

 of the eyelid it becomes thinner, and is manifestly continuous with the epidermis that invests the 

 scales in the vicinity of the orbit. This corneous lamella, by its solidity, is well adapted to defend the 

 eye, and it is this which becomes detached and cast off with the slough of the Snake when it moults 

 its skin. Secondly, beneath this epidermic layer is a second membrane, which is the middle tunic 

 of the eyelid. This is very delicate and soft, and perfectly transparent in the centre, but towards 





VISCERA OF A SERPENT. 



(a) Mouth : (6) Gullet; (c) Tracbsa; (d) Lung; (e) Liver; (/) Stomach and Intestine; (g) Egg; ift) Ovary; (t) Cloaca ; (fc) Vent. 



its circumference it encloses some opaque whitish fibres, supposed by Cloquet to be muscular. This 

 layer, at the margin of the orbit, is manifestly continuous with the skin ; internally it is lined by the 

 third layer, which is mucous, being, in fact, the membrana conjunctiva, which is reflected on to it 

 from the surface of the eyeball. All around the circumference of the eyelid there is a whitish, 

 granular, transparent substance, the nature of which is apparently glandular. 



The conjunctiva lines not only the internal surface of the eyelid, but also a large portion of the 

 cavity of the orbit, from which it is reflected on to the front of the eyeball, thus forming a complete 

 sac without any opening externally. 



The skin comes off the eye during the periodical moult of the cuticle of the body, and for 

 some little time before it looks dull and discoloured ; and when it has been cast, the new covering is 

 perfect in its transparency. 



During the moult the Snakes hide up or are quiescent, and the whole skin comes off in one or 

 more pieces. 



In conclusion, it may be remarked that the Ophidia have not a great geological age, and the 

 first lived in the early Tertiary age. The remains of a Snake belonging to the Python group, 

 twelve feet in length, were discovered at Sheppey ; others of a Boa, twenty feet in length, came to 

 light at Bracklesham. The vertebrae are perfect, and they belong to the fossil genus Palseophis. 

 Others were found at Hordwell in higher strata. In later Tertiary deposits the presence of a 



