BRAIN AND CRANIAL NERVES OF BDELLOSTOMA DOMBEYI, 175 
outside the cranium, acusticus 6 lies for a little while im- 
mediately in contact with the first spino-occipital nerve. ‘T'his 
is apparently one reason for Fiirbringer’s calling acusticus b 
the first spino-occipital nerve, in spite of the fact that it 
arises from the acusticus centre of the medulla. In regard to 
his possible ventral root to this nerve, which he admits not 
having been able to trace as far as the skull, I find nothing 
whatever answering to it, unless, indeed, he has in mind one 
of the separated sets of acusticus fibres that enter the acusti- 
cus ganglion from the ventral part of the lateral surface of 
the medulla. 
The First Spino-occipital Nerve.—The roots of this 
nerve are seen emerging from and entering the spinal cord 
immediately caudad of the last root of the vagus, in that 
transition region where the medulla ends and the cord begins. 
It has one sensory root and two motor ones, the sensory roota 
trifle the most anterior of the three. The sensory and dorsal 
roots curve away from each other to admit of the passage be- 
tween them of the glosso-pharyngeusand vagus, and then 
approach each other as they reach the cranial wall. Here a 
curious thing happens: the sensory root divides, passing the 
wall in two sets of fibres, through two distinct foramina. 
The anterior set has a small ganglion, apparently apart from 
the main ganglion, lying in or inside the wall. After passing 
the wall both strands unite to enter the main ganglion of the 
nerve. ‘lhe two motor roots divide also, passing the wall 
through three foramina and uniting again on the other side, 
and motor and sensory roots unite to form one nerve-trunk 
laterad of the ganglion. It is possible that this division of 
the roots in passing the wall indicates the fusion in the first 
spino-occipital of two distinct nerves, and that study of 
different stages of embryos will throw some light on the 
question. ‘The main trunk of the nerve runs cephalo-laterad, 
then, bending ventrad, it divides into two branches, that run 
ventro-cephalad on the inner face of the lateral longitudinal 
body muscle, supplying finally the lateral body muscles and 
the skin. 
