BRAIN AND CRANIAL NERVES OF BDELLOSTOMA DOMBEYI. 178 
of the other. Once outside the cranium the glosso- 
pharyngeus and vagus run together in the same sheath, 
and a few millimetres beyond the capsule each gives a few 
fibres to the trunk of the other. From this point on, how- 
ever, the two nerves may easily be dissected apart. ‘The 
glosso-pharyngeal ganglion is small, causing no enlargement 
of the nerve trunk, and lies a little caudad of the brain 
capsule. The glosso-pharyngeus runs in the same sheath 
with the vagus as far as the second branchial arch; then 
separating, it runs ventro-caudad, passes through m. con- 
strictor-pharyngis, into which it sends a couple of 
branches, and so to the pharynx wall, dividing into several 
branches, and innervating the side of the pharynx near the 
end of the backward position of the second branchial arch. 
N. Vagus.—The vagus is the most posterior of the 
cranial nerves of Bdellostoma, arising from the caudal end 
of the medulla by four or five roots. ‘These roots run caudo- 
laterad as separate, though close lying, strands, passing 
between the dorsal and ventral roots of the first and second 
spinal nerves, to the wall of the brain capsule. After the 
give and take of fibres with the glosso-pharyngeus the 
vagus runs straight caudad, near to the notochord, until it 
nears the first gill sac. It has no ganglion near the 
cranium, although a few scattered ganglion cells may be . 
found near the brain, and also outside the cranial wall. In 
the region of the branchial rami, however, these cells occur 
in great numbers. ‘They are rather smaller than the cells of 
the Gasserian ganglion, are of a long, oval shape, as though 
compressed by the nerve, and are arranged in longitudinal 
strands. These strands are found from cephalad of the first 
to caudad of the last branchial ramus, and le all through the 
thickness of the nerve, but are more plentiful at the periphery 
than at the centre. All of the gill sacs are innervated in 
the same way. A ramus branchialis is given off that 
divides into an interior and exterior branch. ‘The interior 
branch runs to the duct connecting the gill sac with the 
cesophagus, and divides again into dorsal and ventral rami. 
