IV. OF EANA PIPIENS. 35 



must be regarded as the homologue of the " inferior laryngeal " or " recurrent " 

 nerve of the human anatomist. That this homology is correct is still further 

 indicated by the influence of galvanism, which, when applied high up on the sides 

 of the neck, causes contraction of the laryngeal muscles. No superior laryngeal 

 was detected. A little lower down than the origin of the recurrent branch, the 

 whole trunk divides into two fasciculi of nervous fibres, one of which forms the 

 cesophageal plexus, and the other is readily traced to the heart and lungs. 



From the preceding description, it appears that the vagus arises from the lateral 

 portion of the medulla oblongata, the only distinction between its root fibres being 

 the slight separation of the anterior ones from the rest, which arise nearer the 

 median line on the motor side of the chord. All its fibres appear to enter the gan- 

 glion ; its branches are, 1. to the skin behind the tympanum and over the scap- 

 ula ; 2. an anastomosing branch to one from the trigeminus forming the " facial " ; 

 3. the glosso-pharyngeal ; 4. the splanchnic portion, distributed to the heart, lungs, 

 oesophagus, and stomach. Of the terminal filaments of its different trunks, some 

 are distributed to the skin, others to mucous membranes, as to the oesophagus, 

 tongue, and probably to the respiratory passages ; there are also motor filaments to 

 the stylo-hyoid, to the larynx, and to the spinal muscles immediately above its gan- 

 glion ; these muscles it causes to contract when stimulated by galvanism. 



The vagus nerve has been quite differently described by different anatomists, and 

 it is only required that their descriptions should be placed side by side to render 

 evident their occasional inconsistency. Cuvier, whose accuracy is generally so ad- 

 mirable, in describing this nerve seems to speak from analogy rather than personal 

 observation. He speaks of its " accessory branch " as if it were a distinct trunk, 

 when he says, " The accessory is found in all orders of Reptiles, and is arranged as 

 in Birds." * He further states, " From the ganglion of the vagus in Frogs is given 

 off a nerve for the muscles of the jaws, and another for the tongue " ; the latter 

 has just been shown to exist, but I have never traced any branches to the muscles 

 of the jaws, nor have these muscles contracted when the vagus has been stimulated 

 by galvanism. Opposed to this statement is the fact that the trigeminal branches 

 are distributed to the muscles of mastication, and that they contract when the tri- 

 geminus is galvanized. 



Wagner, in speaking of the vagus, says : " Some very delicate nervous radicles, 

 arising from the inferior tracts of the medulla oblongata near to its anterior fissure, 

 unite with it and appear to correspond with the glosso-pharyngeal." J- This glosso- 

 pharyngeal is one of the principal trunks from the ganglion, and cannot be iden- 

 tified with either of the bundles of roots ; it has been shown to be a sensitive and 

 not a motor nerve, as it would be were Wagner's description correct, which makes 

 it arise near the anterior fissure. 



Longet states, that " in Frogs there is given off from the ganglion of the vagus 

 a branch which is distributed to the muscles of the jaws." J This is a repetition 

 of the statement of Cuvier. 



* Legons d'Anat. Comp., Tom. III. p. 226. J Syst. Nerveuse, Tom. II. p. 371. 



t Comp. Anat. of Verteb. Animals, p. 151, Am. ed. 



