BRAIN AND CRANIAL NERVES OF BDELLOSTOMA DOMBEYI. 165 
foramen. Once outside, the sensory fibres enter the Gasserian 
ganglion, while the motor fibres run, a compact bundle, along 
the ganglion’s ventral surface. The ganglion itself is cylin- 
drical in shape, its long axis directed cephalo-caudad ; it lies 
just outside the craninm, and extends from the anterior end 
of the cerebellum to about the middle of the olfactory lobes. 
The ophthalmic and maxillo-mandibular parts of the ganglion 
overlap each other, the former extending farther cephalad, 
and not so far caudad as the latter. The ophthalmic cells 
of the ganglion, like the ophthalmic fibres of the nerve, lie 
dorso-mediad of the maxillo-mandibular portion. 
R. Ophthalmicus.—This first branch of the Trige- 
minus is purely sensory. P. Fiirbringer declares that it has 
a few motor fibres, but I have found absolutely no trace of 
them, either in the origin or distribution of the branch, 
whether working with sections or by dissection. After 
leaving the ganglion the ophthalmicus runs forward, passing 
dorsad of the optic nerve, between the eye and the skull. 
Immediately in front of the eye it gives off a stout supra- 
orbital branch, r. ophthalmicus cutaneus (r. cutaneus 
superficialis posterior, P. Fiirbringer; r. dorsalis, 
Bowers, 1900). This branch runs dorsad between the 
muscles, appearing on the surface of the head muscles just 
cephalad of the eye. Running cephalo-laterad across the 
subdermal lymph space, it reaches the skin, runs cephalad 
immediately under it for some millimetres, and divides and 
subdivides into numerous fine branches, innervating the skin 
on the dorsal and lateral surfaces between the levels of’ the 
third tentacle and the anterior end of the nasal capsule (fig. 
14). About half way from the Gasserian ganglion to the 
head, the main trunk of the ophthalmicus divides into a 
superficial and a deep branch. The superficial branch, which 
is the smaller of the two, runs forward near the nasal tube, 
and along the dorsal surface of m. palato-ethmoideo- 
superficialis (the names of the various muscles are those 
given by Fiirbringer). On reaching the anterior third of the 
nasal tube it divides, sending one, or possibly two small 
