REPTILIA. 247 



one piece, as may be seen to great advantage in the case of the Ophidia. 

 This epithelium is continuous over the cornea in the serpent, and comes 

 off from the latter in a sub-transparent disk like a watch-glass. It is to an 

 opacity resulting from the partial separation of this epithelium from the 

 subjacent cornea that the temporary blindness of these animals is due. 

 Some of the naked reptiles are provided with glands, distributed partially 

 or entirely over the whole surface, from which a more or less acrid juice 

 exudes. This may be seen conspicuously in the toad, and the salamanders 

 of the genus Amhystonia. 



The apparatus of hearing also exhibits a condition intermediate between 

 that of the fish and the bird. In the fish there is no external ear and no 

 tympanum, the apparatus being represented only by the internal ear. A 

 tympanum is observed, for the first time, in the anourous batrachians ; and 

 a meatus exterior to this in most of the Squamifera, the Ophidia excepted. 

 The apparatus of vision is not very highly developed. The sclerotic mem- 

 brane, in some cases, has a bony ring, developed either in one piece or in 

 several, as in birds. The nasal apparatus is but slightly developed : the 

 posterior nares perforate the palatal bones. The tongue is sometimes thick 

 and fleshy, in which case it generally serves as an organ of prehension, as 

 in the Batrachia, which catch their insect prey in many cases by means of 

 a viscid secretion borne in the tip of the tongue. In the chameleon the 

 tongue can be protruded to a great length for the same purpose. In 

 general, this organ is thin and horny, or cartilaginous. It is sometimes 

 bifurcated, as in the serpents. 



All reptiles, the Chelonia, and some of the caudate batrachians excepted, 

 have teeth, whose office is rather one of prehension than of mastication. 

 These teeth are either inserted in sockets, as in the Rhizodonta, represented 

 by the alligator ; or, secondly, anchylosed to processes of the jaws ; or, 

 thirdly, attached to the inside of a thin vertical plate passing round the 

 mouth. Teeth may also exist in the vomer, as in the North American 

 salamanders. The peculiarities of the teeth in serpents will be treated of 

 in the appropriate place. 



There is but slight development of salivary glands in most reptiles ; owing 

 to the great size of the throat, the food is gulped down almost immediately, 

 without remaining in the mouth. The oesophagus expands into the 

 stomach, from which it is, in many cases, scarcely distinguishable. The 

 most striking exception is found in the alligator, whose stomach presents a 

 very strong resemblance to the muscular gizzard of a bird. The intestinal 

 canal is short and without caecum. A slight constriction only separates 

 the greater from the lesser intestine. The faeces and urinary secretions 

 are all emptied into an expansion of the rectum, the cloaca ; and there is 

 but one orifice of discharge for all secretions and excretions. Through, or 

 into, the same cloaca, pass the oviducts of the female and the vasa 

 deferentia of the male. 



The organ of voice is not generally distributed, occurring to any extent 

 only in the anourous batrachians and the crocodiles. The hiss of the 

 serpent and tortoise can hardly be termed voice. 



451 



