50 Journal of Comparative Neurology. 



As the lateral line VII root is traced through the foramen in 

 the auditory capsule, a compact bundle of finer fibers is seen in 

 its mesial portion. These fine fibers are followed in among a 

 group of very large ganglion cells which is crowded into the 

 mesial angle of the auditory capsule, beneath the lateral line 

 and VIII roots. The origin of the fine fibers from these large 

 cells is entirely clear in both haematoxylin and Golgi prepara- 

 tions. The cells are in part crowded among the fibers of the 

 VIII root and numerous very fine fibers enter the medulla 

 among the VIII fibers and pierce the acusticum and spinal V 

 tract to reach the fasciculus communis as already described (p. 

 24). This is the root and ganglion of the communis VII which 

 has been overlooked by all previous workers. The further 

 course of this component peripherally I have been unable to 

 work out in haematoxylin preparations owing to its small size. 



3. The trigeminus. 



This requires only passing mention because of its simple ar- 

 rangement. The large sensory root emerges from the cranium 

 through a foramen in front of the auditory capsule and bears a 

 large ganglion of medium large cells, which is divided into 

 nearly separate dorsal and ventral limbs. The dorsal limb be- 

 longs to the ophthalmic ramus, the ventral to the maxillary and 

 mandibular. 



The description of the sense organs and nerves shows that: 



1. There are both lateral line organs and end-buds in the 

 skin of Petromyzon. 



2. The lateral line organs are numerous well formed pit 

 organs, and have an arrangement very similar to that in other 

 fishes. They are innervated by a special system of nerves 

 which constitute rami or components corresponding for the 

 most part to the lateral line nerves of other fishes. This system 

 of nerves and its brain center are very large in accordance with 

 the large number of end organs. 



3. There is a large post-auditory lateral line root as in 

 other fishes. This root supplies the larger part of the fibers for 

 the innervation of the pit organs dorsal to the gill slits and on 

 the trunk. 



