i:. -.-.. 



HERPETOLOGY. 



singular species the proteus, in which the eyeballs are 

 so covered with the integuments, as not to be visible 

 till these have been removed. 



In the tortoise tribes there is a bony ring, composed 

 of thin plates at the anterior part of the sclerotic coat; 

 and a similar structure occurs in frogs, chameleons, 

 the guana, and some other saurians. The iris is vari- 

 ously coloured, but generally yellow, red, or brown. 

 The pupil varies in figure. In the crocodile it resem- 

 bles that of the cat, being vertically oblong; in frogs 

 and geckos it is rhomboidal ; and in tortoises, the cha- 

 meleon, and common lizards, it is round. The cry- 

 stalline lens resembles that of fishes in its spheroidal 

 figure. 



that 'of frogiuid toads has a smootlTslimy surface. The Besides the two eye-lids common to reptiles, and the 

 chameleon has the tongue of a cylindrical form, covered superior classes of animals, the former have, like birds, 

 on it* surface with deep regular transverse furrows ; 



it is covered on the upper part with long soft 



hr, giving it the appearance of velvet. In 

 crocodile*, these papilla- are extremely short, and more 

 like wrinkle*. In these animals it is entirely fleshy, 

 but is ,,0 completely attached by the point and edges 

 to the basilar or lower jaw, as to admit of scarcely any 

 motion ; and it was long doubted whether crocodiles 

 had a tongue. In stclliones, again, it is very moveable ; 

 and in the common lizards, and the tupinambes, it is 

 considerably extensile. In these latter reptiles, the 

 tongue terminates in two long flexible cartilaginous 

 points ; and in the skinks and geckos it is notched at 

 the tip. 



The tongue of salamanders is rough with papillae, but 



logy 

 Reptiles. 



and it is so constructed, as to be easily thrust out of the 

 month, to collect the proper food of the animal. 



The organ* of smelling are imperfect, and consist 

 chiefly of cavities opening in front of the snout, and 

 communicating backward with the mouth, lined like 

 the nostrils of mammalia with a pituitary membrane, 

 for the ramification of the nerves. This membrane is 

 in several species divided into several folds, supported 

 bv bony plates. Tortoises have three of these. The 

 external nostrils are furnished with muscular fibres, by 

 which they may be occasionally contracted and dilated. 

 The nostrils are very close together in crocodiles, while 

 in some of the other saurians, as the tupinambes, stell- 

 iones, and chameleons, they are more apart and late- 

 ral. In the tortoises, they are very small and close to- 

 gether ; and they are also extremely small in salaman- 

 ders. In short, from the small extent of the nasal ca- 

 vities in reptiles, compared with those in quadrupeds, 

 it appears that they are rather organs of respiration 

 than of smelling. 



These animals have, as we before hinted, no auri- 

 cles or external ears, though their internal organs 

 of hearing are sufficiently apparent. These consist of 

 a tympanum, (except in the salamander,) and a laby- 

 rinth with their attending bones and cavities. In tur- 

 tles the membrane of the tympanum is cartilaginous, 

 and covered externally by the integuments. The tym- 

 panum contains only a single little bone, and from it 

 proceeds a Eustachian tube. In this order there are 

 semicircular canals. The saurians, with the exception 

 of the salamander, have the same parts, and several 

 little bones, besides several soft stony substances in the 

 vestibule. The crocodile is the only instance among 

 reptiles, in which there is any appearance of external 

 passage to the organ of hearing. The batracians, espe- 

 cially frogs, have a large membrane of the tympanum, 

 level with the surface of the body. The tympanum 

 contains two cartilaginous ossicles, and has a wide open- 

 it' the Eustachian tube next the throat. The ves- 

 tibule contains rudiments of those soft stony substances 

 just mentioned, as occurring in the saurians. In the 

 salamander, the vestibule contains one of these stony 

 bodies, and the oval hole leading to the labyrinth is 

 losed by cartilage. In general the vestibule and mem- 

 ! canals in these animals are much smaller than 

 the bony or cartilaginous cavities in which they are 

 contained. 



There is, we believe, only one instance in reptiles 

 where the eyes appear of little use. This is in that 



a third, or nictitating membrane, which is vertical in 

 tortoises and crocodiles, but horizontal in frogs. In 

 the crocodile there is a bony substance in the upper 

 eye-lid. In the common lizards, instead of eye-lids, 

 there is a kind of circular veil extended before the eye, 

 with a sphincter muscle by which it may be closed. 



There is considerable variety among reptiles with 

 respect to the lachrymal gland. Turtles have it very 

 large, and situated at the lateral or posterior angle. In 

 the fresh water tortoises again, as well as in frogs and 

 toads, there are two small blackish glands. 



Thus it appears that the eyes of reptiles are well 

 adapted to perfect vision, and provided with ample 

 defence against the too stimulating power of the rays 

 of light. It i well known that many of them are very 

 quick in perceiving their prey ; and some species, as the 

 green lizard and green frog, appear extremely fond of 

 the brightest light. Some few, however, shun the 

 day-light, and seek their prey chiefly by night, having 

 for this purpose the power of contracting or dilating 

 the pupil in a very considerable degree. It is said that 

 the chameleon can move both eyes at once, in different 

 directions, a circumstance scarcely noticed in any other 

 animal. 



The general phenomena respecting the nervous sys- 

 tern of reptiles, and the influence of the brain on the 

 other organic functions, cannot properly be considered 

 till these functions shall have been examined. The 

 remarkable tenacity of life in reptiles, their great re- 

 productive power, and the phenomena of the torpid 

 state which they undergo, all of which are more or less 

 connected with the nervous system, must also be de- 

 ferred till we have treated of the functions of circula- 

 tion and respiration. 



CHAP. III. 



Of Digestion in Reptiles. 



DIGESTION in reptiles is divisible into what we may 

 call prehension, deglutition, and digestion, properly so 

 called. * We shall here consider the organs and phe- 

 nomena of these functions, in the order in which we 

 have named them. 



We have seen that the mouth of the cltelonians is fur- 

 mshed with mandibles. These close over each other 

 somewhat like the parts of a box, and frequently have 

 their edges so deeply indented, as to have led to the 

 mistake that some tortoises have teeth. The horny 





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