Houser, Zhe Neurones of a Selachian. gI 
table jungle. The surface of a dendrite bears a few gemmules, 
together with certain small knobs and elevations of various 
shapes. 
The internal organization of a neurone from the right lobus 
vagi is shown in Fig. 46. The nucleuS is always large in pro- 
portion to the bulk of the cell. In some instances there is only 
a thin film of cytoplasm enclosing it at certain points. The 
nucleus is a more or less perfect oval, holding one or more 
nucleoli. The chromatin is distributed in a few thin, branch- 
ing strands which give the appearance of joining in some parts 
of the nucleus. The chromatin never stains intensely in these 
neurones, and so the nucleus is represented by light coloration 
in the figure. | 
The cytoplasm lies principally in the broad areas where 
the cell-body merges into the dendrites. Its tigroid substance 
is never collected into large masses. In the region of the nu- 
cleus, the tigroid material is chiefly in the condition of medium- 
sized granules, with a few small triangles intercalated. The 
dendrites have fusiform or linear tigroids scattered at irregular 
intervals. A very small axone-hillock gives origin to the 
axone. Inthe specimen figured, this lies at the side of the 
most massive dendrite, but this location is not the rule for these 
neurones. 
b. Termination of Communis Fibres. —By far the greater 
number of the communis fibres from the VII, IX, and X nerves 
pass directly to their termination in the lobus vagi, a few, only, 
entering the fasciculus communis, described below. 
Fibres penetrate the lobus vagi for ultimate termination 
chiefly from the dorsal side (Fig. 2, ¢. f.). They reach this 
position by a sweeping curve which carries them to an ever 
higher level as they run inward from the exterior. These in- 
coming fibres constitute a thin stratum next the limitans in- 
_terna, the neurones lying just beneath. The final arborization 
occurs near the body of some neurone. It is of a narrowly 
branching type, with fine, bristle-like twigs terminating the 
branches (Fig. 4, c.f). 
¢. The Fasciculus Communis.—This remarkable tract was 
U 
