THE CRANIAL NERVES. 83 
facial: IX, glossopharyngeal: Xa, laryngeal branch of pneumogastric: Xb, 
pulmonary branch of pneumogastric : Xc, cardiac branch of pneumogastric : 
Xd, gastric branch of pneumogastric: 2, transverse process of second ver- 
tebra: 3, transverse process of third vertebra. 
5. The trigeminal: the largest of the cranial nerves in the 
frog. Arises from the side of the anterior part of the 
medulla, and runs outwards and forwards to the skull 
wall ; just before reaching this it expands into a large 
swelling—the Gasserian ganglion. It then passes 
through the skull wall immediately in front of the 
auditory capsule, and divides at once into two main 
branches :— 
i, The ramus ophthalmicus: runs forward through 
the orbit lying close to its inner side, between 
the skull wall and the eye. It lies beneath the 
rectus superior, but above all the other muscles 
of the eyeball and the optic nerve. At the 
anterior end of the orbit it divides into two 
branches which passes through the walls of the 
nasal capsule, and supply the skin of the fore 
part of the head. 
To trace this branch dissect from the dorsal surface : cut away 
carefully with scissors the side wall of the cranium ; cut through 
and turn aside the rectus superior, and find the nerve running close 
alongside the skull wall, between it and the eyeball. Trace it for- 
wards to the nose. 
ii, The ramus maxillo-mandibularis: runs directly 
outwards behind the eyeball, in front of the 
auditory capsule and between the temporal and 
pterygoid muscles. After a very short course it 
divides into the maxillary and mandibular nerves. 
To trace this nerve and its branches remove the squamosal bone 
carefully, and find the nerve lying on the pterygoid muscle and 
emmeduately behind the eye. Follow the nerve between the pterygoid 
and temporal muscles to the skull, removing the muscles if necessary ; 
and then trace the branches outwards to their distribution. 
a. The ramus maxillaris: runs forwards and 
outwards in the floor of the orbit, behind 
and below the eyeball, to the margin of the 
upper Jaw which it reaches about midway 
