186 Proceedings of the Royal Physical Society. 
is the Palatine. This in Scylliwm is well developed, but here, owing to the 
short distance from its origin to the roof of the mouth which it serves, it is 
reduced to a tuft of twigs given off a few millimetres from the nerve’s source. 
The course of this Hyomandibular nerve is peculiar. It does not enter the 
orbit at all but runs through the anterior portion of the cartilage of the 
Auditory capsule. ) 7 
The rest of this complex does enter the orbit, as I have said, and there 
divides into four trunks (Fig. 1). Beginning with the most dorsal we have 
the Superficial Ophthalmic (VII and V oph.). This is divisible into two 
bundles which in Scylliwm enter the orbit separately—the individual branches 
of the Facial and J'rigeminal—but here they are enclosed in one sheath. As 
in Scylliwm and all other Selachians, they run dorsal to all other structures 
found in the orbit, and on leaving it spread over the dorsal surface of the 
snout. The VIIth fibres are part of the Lateralis system, and therefore go 
to the sensory canals of that region. 
The second of the four trunks is the Deep Ophthalmic (V prof). This is 
considered by some specialists as a separate cranial nerve, the Profundus, and 
not simply a branch of V. It is absent in Scylliwm, at least as a separate 
trunk. In Acanthias it runs ventral to the Rectus and Obliquus Superiores 
muscles, and in contact with the eyeball. On leaving the orbit it also spreads 
over the dorsal surface of the snout. 
The next trunk is the Mandibular branch of V (V mn.), which, while in 
the orbit, occupies very much the position the Hyomandibular has in other 
forms, 2.c. it runs round the posterior wall, but instead of passing round the 
spiracle it, of course, continues to the corners of the mouth and innervates 
the lower jaw. 
The last of these four trunks into which the anterior portion of the VIIth 
and Vth complex divides is a broad band of nerve fibres running postero- 
anteriorly along the floor of the orbit. This trunk, like its dorsal analogue 
the Superficial Ophthalmic, is composed of fibres from both V and VII, the 
Buccal branch of the latter and the Maxillary branch of the former. At the 
anterior end of the orbit, where they become embedded in the tissue of the 
head, they separate and the Buccal branch of the Facial (VII 0.) runs up and 
supplies the sensory canals while the Maxillary branch of the Trigeminal 
(V ix.) spreads over the whole of the ventral part of the snout. 
‘he only other cranial nerve connected with the Rhombencephalon is the 
Abducens, VI, which emerges about two millimetres from the mid-ventral 
line a little posterior to the root of VIII, and, as always, supplies the Rectus 
Externus muscle. ee 
The Mesencephalon (Figs. 2-5). This division of the brain is shaped, 
