584 



REPTILIA. 



for instance in the Tortoise, the cervical nerves, the brachial 

 plexus, from which are derived the nerves of the anterior extre- 

 mity, the intercostal nerves, and those forming the lumbar and 

 sacral plexuses, are at once distinguishable ; and the correspond- 

 ence between their distribution in the reptile and in the human 

 subject must forcibly strike the student who makes the com- 

 parison. 



(644.) Neither does the sympathetic system of the Reptilla offer 

 any important aberration from that arrangement with which the 

 human anatomist is familiar. The ganglia are smaller in their pro- 

 portionate size; those of the neck and face are, indeed, scarcely per- 

 ceptible : but the thoracic ganglia are found in their usual positions, 

 communicating on the one hand with the spinal nerves, and on the 

 other giving off filaments which form plexuses around the arterial 

 trunks, and ramify extensively to be distributed to the viscera of 

 organic life. 



(645.) The sense of touch in all the members of the class under 

 consideration must, from the nature of their integument, be extremely 

 imperfect : many of them, as for example the Serpent tribes, are, 

 in fact, absolutely deprived of any limbs which can be regarded as 

 tactile organs ; and, even in those forms which are provided with 

 efficient locomotive extremities, they are but ill adapted to exercise 

 the functions of an apparatus of touch. 



The cuticular investments of the body are formed of dense and 

 unyielding materials, consisting, in the higher Reptiles, of broad 

 horny plates, or of imbricated scales. In the Amphibia, indeed, 

 the skin is smooth, and the epidermis only forms a delicate cor- 

 neous film ; yet even in these the cuticle is thrown off at certain 

 seasons of the year, as the old coat becomes too small for the in- 

 creasing size of the animal: a phenomenon which in the Lizard and 

 Serpent tribes is still more remarkably witnessed ; for these animals 

 strip themselves of their old scales as the hand would be drawn out 

 of a glove, and cast away in one piece the entire epidermic inte-. 

 gument, even to the film which covers the transparent cornea of 

 the eye. 



(646.) The urinary excretion in Reptiles becomes of very consi- 

 derable importance, and the structure of the kidneys and excretory 

 ducts proportionately elaborate. The kidneys (fig- 267, o, p) are 

 generally situated very far back, even within the cavity of the pelvis 

 where a sacrum exists, as in the Chelonian and Saurian orders ; and 

 in these tribes they are very partially covered by the peritoneum 



