OF THE MARSIPOBRANCH FISHES. 
401 
On the cranial nerves of Bdellostoma. 
For a detailed account of these, and also of the whole nervous system, the same 
excellent author is referred to ; but I have given an outline figure of the skull with the 
cranial nerves shaded, to help in the determination of the skeletal parts. My own 
dissection of these nerves was made with the help of Muller’s work (‘ Neuro- 
logie,’ III.). I made no attempt to find any filaments of the 3rd, 4th, and 6th. 
The vagus nerve (Plate 10, fig. 4, X.) probably contains the fibres that in higher forms 
are given off as the separate glosso-pharyngeal. Muller does not figure that nerve 
as distinct, nor can I find it. But the vagus is very large, and as its proper related 
structures are removed far backwards, passes directly backwards at right angles 
to the spinal nerves (sp.n 1-3 .). The vagus emerges behind the auditory sac ( au .), 
over the short parachordal. 
The 8th or auditory nerve is not figured; it passes into the auditory capsule 
through the great meatus interims. 
The 7th nerve (VII.) is shown; it finds its way out of the skull in front of the 
auditory capsule, between the “ pedicle ” and the head of the hyomandibular (fig. 2, pel., 
hm.), and turning backwards, burrows under the “shoulder” of the hyomandibular, 
escaping again behind the symplectic region—the hind boundary of the second fenestra 
—and passes down with, and in front of, the descending epi-cerato-hyal bar ( e.hy ., c.hy.). 
The 5th or trigeminal nerve (V.) is immense, and at first sight rather difficult of 
interpretation. I follow Muller’s notation, finding nothing in it to criticise. It is 
seen emerging in front of the auditory capsule over the pedicle {pel). It then breaks 
up into three branches, two of which pass over the subocular fenestra ( s.of ), whilst 
one pierces that membrane behind, and passes under the palato-quadrate cartilage. 
The 1st branch, the orbito-nasal (or ophthcdmic, V 1 .), is very large, and soon breaks up 
into a lesser outer and a larger inner branch. The inner branch then becomes trifid. 
The “ upper maxillary,” or second branch of the trigeminal (V 3 .) is considerably less 
than either of the three branches of the ophthalmic ; it runs over the subocular fenestra, 
and the palato-quadrate cartilage. The “ inferior maxillary,” or third branch (V 3 .), is 
as large as the ophthalmic, and as soon as it has passed through the suborbital fenestra 
it breaks up into four branches, which pass to the lower parts of the head in front. 
The optic nerves (II.) are about a fourth the size of the small maxillary nerve ; 
they pass under the ophthalmic (orbito-nasal), and are distributed to the arrested 
eye-ball (e.), enclosed in the much larger fat body ( c.a .). 
The olfactory nerves (I.) pass through the membranous “cribriform plate,” which is 
in two divisions and oblique. The huge olfactory lobes give off each five nerves 
and these, beginning to bifurcate, pass in a sub-horizontal row, right and left, to the 
olfactory folds ( ol .); here there is a most remarkable anticipation of the Mammalian 
* The outer or fifth bundle of the olfactory nerve lies somewhat under the fourth, and is not shown 
in the figure. 
