Johnston, The Brain of Petromyzon. 49 



not post-auditory components. The interesting question arises, 

 why a part of these organs should be innervated by post-audi- 

 tory components running in the IX trunk. 



The roots, gangha, and rarni of the vagus group are dia- 

 grammatically projected on Fig. 7, and shown in their proper 

 relationship in Fig. 29. 



2. The VII-VIII complex (Figs, 11, 1 1 a, 12, 29). 



The roots of VII and VIII both enter the auditory cap- 

 sule. The VIII has medium sized fibers and a large ganglion 

 of very small cells, together with a few very thick fibers and 

 large cells. The ganglion is dorso-ventrally flattened and is 

 elongated. It is a dense mass of cells and fibers from which 

 two main rami go to the cephalic and caudal portions of the 

 ear. The two lateral line VII roots, arising higher on the wall 

 of the medulla, come down close over the cephalic surface of 

 the VIII roots and ganglion and, coursing forward and down- 

 ward, make their exit from the capsule at the cephalic and 

 mesial angle. The fibers are thick and are easily distinguished 

 from those of VIII or the communis VII. The root bears a 

 large ganglion of medium large cells, the greater part of which 

 lie beneath the auditory capsule, extending both forward and 

 backward. A part of the ganglion cells accompany the root 

 in the foramen and within the auditory capsule. From this 

 ganglion the VII-X anastomosis passes laterally and from the 

 cephalo-lateral angle the large buccal trunk goes ventro-later- 

 ally to supply the pit organs of the infra-orbital line. The 

 anastomosis contains a few fine fibers which pass through the 

 ganglion, coming presumably from the ganglion of the com- 

 munis root to be described below. As the anastomosis passes 

 around the auditory capsule it gives off some fine branches 

 which presumably innervate the pit organs above and in front 

 of the first gill slit. Miss Alcock has described two other 

 nerves from the front end of the ganglion which Cole ('98) in- 

 terprets as otic and ophthalmicus superficialis. From the pos- 

 terior portion of the ganglion arises the ramus hyoideus which 

 divides into a branchial nerve to the hyoid segment and a ramus 

 branchialis profundus as described by Alcock. 



