360 H. W. NORRIS AND SALLY P. HUGHES 



THE VAGUS NERVE 



1 . The lateral-line roots and ganglia of the vagus nerve 



The roots of the vagus nerve in their entirety when seen in a 

 lateral view (figs. 24, 48, and 51) form a wedge-like sheet of 

 fibers on the side of the medulla. Converging at the postero- 

 ventral angle of the wedge, the combined fibers form a compact 

 column that produces a hollowing out of the mesial wall of the 

 ear capsule and forms a recess, the beginning of a canal or cham- 

 ber in the extreme posterior portion of the ventromesial part of 

 the ear capsule. This chamber in which the combined lateral- 

 line and visceral sensory ganglia for the greater part lie, opens 

 posteriorly at the border of the occipital condyle. 



As indicated in a previous section, the lateral-line element in 

 the ninth nerve enters the brain immediately anterior and ven- 

 tral to the anterior lateral-line roots of the vagus (figs. 24 and 

 51). Within the brain the vagus lateral-line fibers may be traced 

 far anteriorly as a wedge-shaped (in cross-section) tract reaching 

 from the periphery of the brain inward as far as the lateral border 

 of the visceral lobe. On entering the brain the lateral-line fibers 

 of the vagus all turn anteriorly (fig. 40). Farther anteriorly the 

 tract appears to be made up of scattered bundles and finally 

 becomes indistinguishable from the other medullated tracts of 

 the acusticum. Peripherally, the root fibers form a broad 

 ribbon-like band lateral to the brain, covering the anterior roots 

 of the vagus proper lying mesially. Farther posteriorly, the 

 lateral-line root drops ventrally so that the more posterior roots 

 of the vagus are exposed. Still farther posteriorly and ending 

 in the ganglion, the root becomes more compact covering merely 

 the ventral border of the vagus roots (figs. 24, 48, and 51). 



The lateral-line ganglion of the vagus shows evidence of a 

 segmentation into three parts. The first is the more anterior 

 part of the vagal ganglionic complex, a slender column of cells 

 that gives rise to the supratemporal ramus. Just posterior to 

 this first cell mass and for some distance in contact with it lies 

 the major part of the ganglion, two scarcely separable masses of 

 cells, from the anterior of which arise the fibers of the ramus 



