AMPHIBIA. 47 



resembling that in the higher classes for giving off the nerves of the posterior 

 extremities, for the spinal nerves, entering it, correspond with these, inasmuch as they 

 have their origin from the inferior part of the spinal cord, just above that from which 

 the caudal nerves usually issue. 



In the sympathetic nerve there are several varieties in different genera of 

 amphibia. In the crocodile and alligator the sympathetic nerve is continued down 

 the neck in a canal like that containing the vertebral artery in birds. In the turtle 

 and snake, there is not a canal in which the sympathetic passes with a vertebral 

 artery ; the branch, according with the one ascending from the first thoracic ganglion 

 in mammalia, passes on the outside of the spine in the turtle, and in the snake, 

 in an incomplete canal near the connexion of the ribs with the eleven superior 

 vertebrae. In the turtle, there is a prolongation, but no cervical ganglia ; it is 

 more or less closely attached to the par vagum, but does not exist in the snake, 

 or, if it does, its small size prevents its being easily recognised and distinctly 

 separated. The sympathetic does not appear to be more highly evolved than in 

 fishes ; for in the turtle, the ganglia attached to the prolongation are very diminutive, 

 except the first thoracic, which is broad, and has a membranous character ; and 

 in the snake, except at its superior part, where there is one remarkable ganglion 

 connected with the trunk of the par vagum, and several smaller ones at the junction 

 of the sympathetic with branches of the second trunk of the fifth proceeding to the 

 palate and nose; in the snake for some distance there are very slight plexiform 

 junctions of the branches from the spinal nerves which join the prolongation ; but 

 these plexuses are in some parts more complicated, and in both the snake and turtle 

 exist for giving off the nerves to the viscera instead of the close and fleshy semilunar 

 ganglia. In the frog as in the snake, except the first cervical, no other distinct 

 ganglia of the sympathetic exist, and the branches destined for the abdominal viscera 

 also join a prolongation from which the splanchnic branches are derived. 



The brain of amphibia, compared with that of fishes, is rather more complicated. 

 It has to sustain respiratory processes through capacious lungs ; and these acts are so 

 forcible in the turtle, as to seem to be promoted more by a voluntary than an 



