578 REPTILIA. 



numerous filaments : there is, consequently, no cribriform plate to 

 the ethmoid bone ; but the nerve of each side (Jig. 264, e) 

 is received into a simple canal, partly osseous and partly car- 

 tilaginous, through which it is conducted to the cavity of the 

 nose. 



The nasal apparatus of Reptiles differs from that of Fishes in 

 one important particular. Breathing air as these creatures do, 

 the sense of smell now becomes connected with the respiratory 

 function; and, a communication being established between the 

 nasal cavities and the larynx, the air which passes through this 

 channel into the lungs must necessarily come in contact with 

 the sentient surface formed by those portions of the lining mem- 

 brane of the nose to which the nerves of smell are distributed; 

 and, in proportion as the extent of that surface becomes developed, 

 the power of appreciating the presence of odorous particles in 

 the atmosphere will necessarily be increased. The physiologist 

 is thus enabled to estimate with great exactness the relative per- 

 fection of the sense of smell in different classes, or even in dif- 

 ferent families of the air-breathing Vertebrata, simply by observing 

 the complication and extent of surface presented by the lining 

 membrane of the olfactory organ. 



Taking this as our guide, we must suppose that in all Rep- 

 tiles the sense in question is extremely obtuse, since in these 

 creatures there are neither turbinated bones nor ethmoidal plates 

 as yet distinguishable ; a few folds of the membrane lining the 

 nose, even in those species which are most highly gifted in 

 this particular, being the only provision for extending the olfac- 

 tory surface ; and in many cases, as for example in the Am- 

 phibia, the nose seems merely a simple canal leading into the 

 mouth. 



On reaching the nasal cavity, the olfactory nerve spreads out 

 into delicate filaments (Jig. 264, d), which are distributed to the 

 Schneiderean membrane covering the septum and upper part of 

 the nose. 



(634.) The optic nerves of Reptiles (Jig. 262, n), soon after 

 their origin, become confounded together by a commissure, in 

 the same way as in the human subject; and, again separating, they 

 are continued through the optic foramina to the eyes. 



The eye-ball itself presents few peculiarities in its structure. 

 In the Tortoise, and many Lizards, the sclerotic contains a circle 

 of bony plates imbedded in its substance, and surrounding its 



