BRAIN AND CRANIAL NERVES OF BDELLOSTOMA DOMBEYI. 169 
glossus-superficialis, and m. copulo-glossus-pro- 
fundus, and a posterior branch to the “club muscle,” the 
retractor of the lower jaw. This last branch also divides 
into two, an outer and an inner. The outer branch runs 
straight caudad in the fascia of the outer circular muscle, 
and on reaching the muscle itself divides into dorsal 
and ventral branches. The ventral branch runs on the 
upper surface of the circular muscle just beneath the long 
central muscle, sending off tiny threads all along the way. 
At the end of the circular muscle it passes diagonally 
upward, running across m. perpendicularis. The dorsal 
branch runs in the depths of the dorsal part of the circular 
muscle just over the central muscle, and it also gives off tiny 
threads along the way. About half way back it anastomoses 
with its fellow of the opposite side, and from this anasto- 
mosis three or four strands are given off, all running straight 
backward. Among them are two principal ones, a dorsal 
strand that passes very obliquely upward and ends at the 
broad dorsal tendon of the circular muscle, and a ventral 
one that remains on the deeper level and, running through 
m. perpendicularis, ends in the long central muscle. 
The inner branch goes back a little, then turns suddenly 
mediad and enters the tendon of the long central muscle, 
running backward in the tendon. 
Caudad of r. mandibularis the main trunk of the 
trigeminus gives off a small motor branch to m. velo- 
quadratus. 
N. Facialis.—The facial nerve is exceedingly small and 
fragile, very difficult to dissect out, and hard to follow to its 
termination even in sections. It leaves the medulla caudad 
of acusticus a and acusticus b, passes through the 
acusticus ganglion, and breaks through the cranial wall just 
cephalad of the ear capsule. Heematoxylin sections give no 
hint as to its containing more than motor and communis 
fibres. On leaving the cranium the facialis runs caudo- 
ventrad under the hyoid arch. Its ganglion lies close to the 
ear capsule, and is always present, though variable in shape, 
