CRANIAL NERVES 191 



with the sympathetic system. In the myxinoids the intestinal nerves of the 

 two sides unite dorsal to the alimentary canal and continue in that position 

 back to the anus. In some teleosts (plectognaths) the lateralis nerve is greatly 

 reduced. In those bony fishes where the sense organs of the lateral line have 

 migrated above the division between epi- and hypaxial muscles, they may be 

 accompanied by a second, the superficial lateralis trunk. 



With the absence of gills in the amniotes and their loss in the 

 higher amphibia the lateralis elements disappear and the branchial 

 nerves are reduced, though parts are present as pharyngeal nerves. 

 On the intestinal nerve is a nodose ganglion (fig. 196, w) which may 

 be the equivalent of the epibranchial ganglion of teleosts. In 

 Sphenodon the intestinal trunk gives off a series of three metameric 

 nerves (fig. 196) which, in their relations to the aortic arches, recall 



Fig. 196. — Diagram of the neck region of Sphenodon, after Van Bemmeln. Arteries 

 white, pharyngeal derivatives dotted, nerves black, ao, dorsal aorta; c, carotid gland; 

 ec, external carotid; gc, cervical ganglion of sympathetic; ic, internal carotid; li, Is, 

 inferior and superior laryngeal nerves; n, ganglion nodosum; pa, pulmonary artery; 

 pg, petrosal ganglion; sy, sympathetic trunk; /, thymus; tr, thyreoid. 



the branchial nerves of fishes. Apparently the first and third of 

 these are represented in the mammals by the superior and inferior 

 laryngeal nerves. 



In the tetrapoda the intestinal branch supplies not only the stom- 

 ach and heart as in the ichthyopsida, but the lungs as well, a point of 

 interest in connexion with the theories of the origin of lungs. The 

 dorsal ramus of the lower fishes is retained as the auricular nerve 

 which unites with the similarly named branch of the ninth. In the 

 higher, as in the lower vertebrates, the vagus is connected at several 

 points with the sjTnpathetic system besides the connexion at the jug- 

 ular ganglion. It may be noted here that, since the vagus is a 

 cranial nerve, its distribution to heart, stomach and lungs, shows 

 that these structures belong morphologically to the head, although 

 they may be far removed from it in the adult. 



