THE DOGFISH 17 



3. The oculomotor is a small nerve which arises in the ventral 

 surface of the optic lobe on each side and passes laterally to the 

 orbit ; it enters the orbit a short distance back of the optic nerve 

 and sends branches to the inferior rectus, the internal rectus, the 

 superior rectus, and the inferior oblique muscles. It may be seen 

 by pressing the side of the skull away from the optic lobes. 



4. The trochlear, or pathetic, nerve is a delicate strand which 

 arises from the laterodorsal surface of the brain between the optic 

 lobe and the cerebellum. It runs forward to the orbit, which it 

 enters above the optic nerve, and goes to the superior oblique 

 muscle. It may be seen emerging from beneath the anterior por- 

 tion of the cerebellum and passing to the orbit. 



5. The trigeminus is a very large nerve which arises from the 

 side of the anterior end of the medulla in such close connection 

 with the seventh and eighth nerves that the three nerves appear to 

 spring from a common root. The trigeminus passes into the orbit 

 and at once divides into four branches. Cut away the wall of 

 the orbit and find these nerves. (1) The uppermost of the four 

 branches is the superficial ophthalmic, which is joined by the cor- 

 responding branch of the seventh nerve and runs forward along 

 the medial wall of the orbit to the ophthalmic foramen near its 

 anterior end. It leaves the orbit through this foramen and runs 

 forward on the dorsal surface of the snout, where it innervates 

 the Lorenzinian ampullae. (2) The second branch is the deep 

 ophthalmic, a slender nerve which passes forward beneath the 

 superficial ophthalmic and, leaving the orbit, is distributed to the 

 skin of the snout. (3) The third branch is the maxillary, a broad 

 flat nerve which is joined with the buccal branch of the seventh 

 nerve and passes obliquely across the floor of the orbit, from which 

 it emerges near its forward end and innervates the skin of the ven- 

 tral surface of the snout. (4) The fourth branch is the mandibular, 

 which arises beneath and behind the maxillary branch and passes 

 along the hinder wall of the orbit to the muscles and the ampullae 

 of the lower jaw. In the smooth dogfish the third and fourth 

 branches are united. 



6. The abducens is a very small nerve which arises from the 

 ventral surface of the medulla near the median line behind the 



