OF THE SKULL IN THE COMMON SNAKE. 
391 
But in the Salmon (“Salmon’s Skull,” Plates 1-3) and in the Pig (“Pig’s Skull,’ 
Plate 28, figs. 1-3) this part is clearly seen; in the Fowl (“Fowl’s Skull,” Plate 81, 
fig. 1) it is represented by the line between the eye (e.) and the sub-ocular bar {pa.). 
I am not certain whether this cleft is quite open within ; if not, its morphological 
importance is the same. 
The ventral region is finished in front by an elegant double fold of skin, separated 
by a rounded emargination at the mid line, which grows from the head across the 
valley between the fore brain and the rudiment of the hemispheres. 
These, together, form the “ naso-frontal process {n.f.p >.) they are attached each to the 
corresponding olfactory dome, at its postero-internal part. These two folds grow more 
together, and receive, afterwards, a double growth of cartilage from the trabeculae — 
the conjoined trabecular cornua, rudiments of the foremost visceral arch. (See Plate 28, 
figs. 6 and 9, c.tr.) 
The relation of the cranial nerves to these ventral (visceral) folds, and their inter- 
vening clefts, is of the utmost importance in the morphological interpretation of the 
parts of the face and throat. 
Leaving out of question for the present those cranial nerves which cannot yet be 
classified, such as the olfactory, optic, and motores oculorum, the rest have very definite 
relations to the folds and clefts of the head.* The trigeminal, facial, glosso-pharyn- 
geal, and vagus nerves (5th, 7th, 9th, and 10th) break up into two or three principal 
branches that run on each side of the clefts. 
Both the facial and trigennial have three main branches; the glosso-pharyngeal two; 
and the vagus as many as there are branchial arches to be supplied by it behind the 
glosso-pharyngeal, this latter nerve supplying the back of the hyoid arch and the 
front of the first branchial. 
The facial nerve (7th), besides sending its main part to the front of the hyoid 
arch, and giving off the chorda tympani branch to the back of the mandible, sends 
forward a third branch, the vidian, which is distributed to the maxillopalatine regions. 
This nerve runs outside and below the first branch of the great trigeminal or 5th, 
whose second and third branches supply the parts round the oral cleft. 
But the first branch of the 5th, the ophthalmic or orbito-nasal, runs over the optic nerve 
into the nasal region, and, whilst the second and third branches in a normal manner fork 
over the oral cleft, the first branch runs in front of the lachrymo-nasal cleft to supply 
the rudimentary terminal arch, whose skeleton is formed by the cornua trabeculae. t 
i 
* The “ portio mollis,” 8tli or auditory nerve, may be a dorsal branch of the facial or seventh 
nerve ; I leave it ont of special consideration here. 
t The later researches of Mr. Balfour (Phil. Trans., 1876, Part II., Plates 16-18, pp. 175-195), 
showing that these nerves are formed in the “ Elasmobranchs ” from epiblast, give ns some hope of a true 
classification of the cranial nerves ; for it now looks as though the olfactory and optic nerves were not so 
widely diverse from the others as was supposed. Dr. A. Milhes Marshall has set this at rest with regard to 
the 1st nerve ; it does arise like the rest (see Quart. Journ. Micr. Soc., vol. 18, new ser., plates 1, 2, pp. 1-31). 
MDCCCLXXVIII. 3 E 
