82 THE NERVOUS SYSTEM OF THE FROG. 
The course of the optic nerve has been fully seen in previous 
dissections. 
3. The motor oculi: a small nerve arising from the ventral 
surface of the brain close to the median line and between 
the crura cerebri. It supplies four of the muscles 
moving the eyeball; wz, the rectus superior, rectus 
internus, rectus inferior, and obliquus inferior. 
Owing to its small size the third nerve is not easy to dissect 
un the frog. 
4, The pathetic or trochlear nerve: a very slender nerve, 
arising from the dorsal surface of the brain between the 
optic lobes and the cerebellum, and supplying the 
obliquus superior muscle of the eyeball. 
The nerve is too small to be dissected satisfactorily in the frog. 
Fig. 18. The trigeminal, facial, glossopharyngeal, and pneumogastric 
nerves of the frog, dissected from the right side. 
a, stomach: e, Eustachian tube: h, hypoglossal nerve : 7, lung : m, second 
spinal nerve: s, sinus venosus: t, squamosal : t.a, truncus arteriosus : u, right 
auricle: v, ventricle: v.c, right vena cava superior: Va, ophthalmic branch 
of trigeminal: Vb, maxillary branch of trigeminal: Vc, mandibular branch 
of trigeminal: Vila, palatine branch of facial; VIIb, hyoidean branch of 
