ORDER OPHIDIA. QQl 



those of the organs which depend on the cerebro-spinal 

 system are, as in the chelonians and batracians, very thick, 

 relatively to the brain. For the rest they have nothing very 

 remarkable. 



All the ophidians have two eyes placed laterally at the 

 right and left of the head. These eyes in appearance are 

 without lids, a slight edging formed by the skin seems to 

 be their only protection. This fact has been remarked at all 

 times, for Aristotle, in his immortal writings, expressly 

 notices this pretended want of mobile and protecting veils 

 of the organ of vision in the serpents, and his opinion has 

 been partaken at divers periods by anatomists and zoologists, 

 and even by M. Cuvier. Nevertheless, recent researches 

 undertaken by M. Cloquet, and verified by our author and 

 by M. Dumeril, have demonstrated that the eye of the 

 ophidians is covered by a single lid, very large and immove- 

 able, and which appears as it were enchased in a projecting 

 frame, which forms around the orbit a variable number of 

 scales, but most usually from seven to eight. 



There is a circular cul-de-sac of no great depth, between 

 this frame and the eyelid, which is itself composed of three 

 membranous leaves placed over each other. 



The first of these leaves is an epidermic plate, elastic, 

 thicker towards the centre than at the circumference, which 

 continues insensibly with the cuticle of the scaly edging of 

 the orbit. This alone is detached, and falls with the rest of 

 the epidermis at the epocha of moulting. 



The second is very fine, soft, and perfectly transparent 

 in the centre. 



The third is formed by the conjunctive membrane or 

 albuginea, which represents a great sac, without external 

 aperture, as in those individuals of the human species in 

 whom is observed that peculiarity of structure denominated 

 by pathologists, anhylohlepharon. 



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