250 VERTEBRATE ZOOLOGY 



Back of the hemispheres is the broad pons with its transverse 

 fibers ; it is the ventral portion of the fourth division of the brain, 

 of which the cerebellum is the dorsal portion. Just in front of it 

 and springing from near the midventral line may be seen, by tilt- 

 ing the brain to one side, the small oculomotor nerves, the third 

 pair of cranial nerves, which pass forward on each side and supply 

 the following muscles of the eyeball : the superior rectus, internal 

 rectus, retractor, inferior rectus, and inferior oblique. From the 

 lateral side of the brain, just in front of the pons on each side, 

 springs the pathetic, or trochlear, nerve, the fourth cranial nerve ; 

 it is a delicate strand which passes forward to the superior oblique 

 muscle of the eyeball. It will be seen when the ventral surface 

 of the brain is studied. 



The large trigeminal nerve, the fifth cranial, springs from the 

 posterior border of the pons by two roots, a small motor and a 

 large sensory root. The large root passes straight forward, and 

 soon enlarges and forms the Gasserian ganglion ; from this three 

 nerves spring, the ophthalmic, the maxillary, and the mandibular ; 

 the small root joins the last-named nerve. The ophthalmic nerve 

 passes into the orbit, where it gives off branches which go to 

 the eyeball, the upper eyelid, and the nose and snout." The maxil- 

 lary nerve emerges from the cranium back of the orbit and 

 gives off branches which go to the lower eyelid, the upper lip and 

 jaw, the palate, and the face. The mandibular nerve leaves the 

 cranial cavity back of the orbit and gives off branches which sup- 

 ply the external ear, the muscles of the jaw, the lower jaw, the 

 lips, and the tongue. 



Just back of the pons will be seen, in the lateral aspect of the 

 brain, a swelling called the trapezoid body, which is at the anterior 

 end of the medulla. Springing from the medulla medial to the 

 trapezoid body is the sixth pair of cranial nerves, the abducens, 

 which pass to the external rectus muscle of the eyeball; these 

 nerves will be seen when the ventral surface of the brain is studied. 



Arising from the lateral surface of the trapezoid body are the 

 facial and auditory nerves,— the seventh and eighth cranial nerves. 

 The facial is the smaller of the two ; it springs from near the base 

 of the trigeminal nerve and passes to the face immediately below 



