The Cranial Nerve Components of Petromyzon. 153 
it is found in some fishes. The neuromast part of it is shown in 
HATSCcHER’sS Fig. 11. 
- In front of the point where the sensory bundle swings across 
the eaudal surface of the motor root, this root runs ventro-laterally 
(319) through the ganglion, dividing the ventral part into lateral 
and mesial portions (Fig. 2). The mesial portion is much smaller 
and consists of the ganglion cells belonging to the sensory bundle 
just mentioned. Between 316 and 312 two rami arise which together 
represent the ramus mandibularis. The more mesial ramus consists 
of motor fibers alone; the more lateral consists of a) all the sensory 
fibers from the mesial part of the ganglion, b) other sensory fibers 
from the lateral part, and e) a small part of the motor root (Fig. 2). 
The mesial, pure motor root runs backward (316—320), downward 
in the velum (324), backward and downward through the longi- 
tudinal muscle which forms the ventral border of the velum to 
450—454, where it descends to the dorsal surface of a transverse 
muscle which covers the dorsal (inner) surface of the ventral earti- 
lage. The cartilage is here semi-lunar in section. Here the nerve 
turns abruptly forward and runs elose upon the surface of this 
muscle, slowly nearing the middle line. It lies just below and 
lateral to a median fold or septum until at 345 it enters a basket- 
work of muscle in this septum. This seems to be a median muscle 
until about 278, where it separates into lateral bundles. As we pass 
