IV. OF RANA PIPIENS. 37 



It is an interesting feature in the anatomy of Batrachian Reptiles, which in so 

 many respects resemble Fishes, that they should have, some of them temporarily 

 and others permanently, a nerve which is strictly analogous to the nervus lateralis 

 of Fishes. It has been found by Van Deen to exist in Proteus, by Meyer in 

 Menopoma, and by Kuhn in Tritons, and probably it exists in all the other Urodels. 

 Among the Anourous Batrachians it was first noticed in Frogs, by Van Deen. 



Its distribution, as it was presented in the tadpoles of R. pipiens, is as follows. 

 (Plate II. Fig. 9.) The vagus escapes through the cartilaginous occiput as a single 

 trunk, and from its ganglion are given off the following branches : 1st. A branch 

 which unites with another from the trigeminus, and forms the facial. 2d. A cutane- 

 ous nerve, distributed to the skin of the neck and that of the branchial region. 

 3d and 4th. Two delicate filaments, which, one of them dividing, furnish three 

 nerves (d), one to each of the branchial arches. 5th. The nervus lateralis (c) ; at its 

 origin, this, like the preceding nerves, is concealed by the spinal muscles attached to 

 the occiput ; having extended outwards as far as the skin, it passes along the side 

 of the abdomen just beneath the edge of the spinal muscles, and is continued along 

 the side of the tail in the groove formed by the union of the upper and lower 

 series of caudal muscular bands. Soon after leaving the vagal ganglion, the 

 nervus lateralis gives off a delicate filament (, 6), which does not appear to have 

 been noticed hitherto, and which is easily traced, if the parts have been macerated 

 in dilute nitric acid ; this branch ascends and is directed backwards till it reaches 

 the base of the fold of skin forming the upper portion of the caudal fin, along the 

 base of which it extends towards its termination. 



While no doubt exists as to the identity of the nervus lateralis, there can be 

 little that the branch just described is identical with the nervus dorsalis of Weber, 

 it being, as in some Fishes, a branch of the vagus ; in the case of Frogs it is wholly 

 cutaneous, there being no muscles connected with the skin, and in Fishes it seems 

 questionable whether this nerve is motor or sensitive. In Cuvier's Comparative 

 Anatomy the following remark occurs in connection with the vagus, which it is of 

 interest to mention here : " Up to the present time, no nerve analogous to the 

 dorsal has been found in Reptiles. Nevertheless, the parietal bones of Saurians 

 are pierced with a foramen like those of Fishes." * 



The observation of the existence of a dorsal nerve gives additional importance to 

 the discovery of the nervus lateralis by Van Deen ; and if to these we add those 

 branches of the vagus described above, which pass along the branchial arches, the 

 analogy of the larvae of Batrachians to Fishes becomes much more striking than 

 there has been reason hitherto to regard it. 



SECTION V. PHILOSOPHICAL ANATOMY OF THE CRANIAL NERVES AND SKULL. 



In the table at the commencement of Section IV., the cranial nerves of Man 

 and Mammals, and those of the Frog, are contrasted ; it is there shown what nerves 

 in the two correspond, and how it is that, by the union of two or more nerves, the 



* Lemons d'Anat. Comp., Tom. III. p. 229. 



6 



