40 AMPHIBIA. 



resemblance to the form of the Gasserian ganglion than in fishes ; the usual cutaneous 

 branches pass through perforations in the bone to the parts beneath the horny covering 

 in the turtle, but this disposition does not exist in the same degree in the snake, and 

 is therefore a peculiarity for corresponding with the conformation of the parts receiving 

 them. The par vagum and glosso-pharyngeal at their origins are not very different 

 from the same in fishes, except that they are not so much connected with the auditory 

 nerve. In the snake, so many communications between the glosso-pharyngeal, par 

 vagum, and ninth, take place before branches are given off to supply any parts, that it 

 is very difficult to determine with precision the destination of each, for the muscles 

 and other structures of the throat are so complicated, and at the same time so con- 

 nected in function, that although the nerves be different at their origins, yet it seems 

 they must be connected for associating the actions of the parts receiving them. In 

 amphibia the par vagum appears to supply almost entirely the heart. When the 

 slight difference between the summit and base of the brain in the turtle and skate is 

 considered, it cannot fail of being remarked that so many more nerves exist in the 

 turtle than in the skate, as the hard portion of the seventh, a more distinct auditory 

 nerve, the ninth and accessory; but the changes attendant on respiration by lungs 

 require more ample provisions in several parts for their completion. 



There is not much difference between the spinal cord of amphibia and fishes, for 

 in both classes it varies with the length and thickness of the body. In the turtle 

 it is flat, and somewhat broader, for giving origin to the nerves of the upper and 

 lower extremities. In the snake it preserves nearly the same thickness throughout, 

 until it reaches towards the tail. In numerous fishes it is thick at the upper part, 

 and gradually diminishes in descending by tapering to the end of the tail ; in longer 

 or shorter kinds it varies according to the quantity of nerves required to issue from it. 

 The spinal nerves of amphibia are not very different from those of fishes, except 

 in the closeness of their origins, especially in the snake, and the more regular 

 communications of the anterior and posterior bundles of each nerve, and having more 

 distinct and fleshy ganglia. In the frog there is one large nerve instead of a number 

 forming the axillary plexus, as in the turtle; in both, however, there is a plexus 



