XVI THE NERVOUS SYSTEM 297 



anterior end of the medulla by a pair of roots which unite 

 in a large prootic ganglion before leaving the skull. This 

 ganglion, which corresponds in part to the Gasserian gan- 

 glion of higher forms, is connected with the sixth and seventh 

 nerves and also the sympathetic. Two branches of the tri- 

 geminus, the ophthalmic and the maxillo-mandibular, emerge 

 from the ganglion, and leave the skull by a foramen in the 

 anterior part of the prootic bone. The former runs along 

 the dorsal side of the orbit, passes through a foramen in the 

 posterior wall of the nasal capsule, and divides into branches, 

 most of which emerge from the nasal capsule again, and are 

 distributed to the skin of the anterior part of the head. The 

 maxillo-mandibular nerve runs outward behind the eye ; it 

 soon divides into the niaxillaris superior and the maxillaris 

 inferior, or 7nandibular. The former runs forward and out- 

 ward below the eye and suppHes the upper lip and adjacent 

 structures. The latter supplies the principal muscles for 

 moving the lower jaw, the lower lips, and skin of the lower 

 side of the mouth. The trigeminus is a mixed nerve, partly 

 sensory and partly motor. 



The sixth nerve, the abducens, arises from the ventral side 

 of the medulla. It joins the prootic ganglion and emerges 

 through the same opening as the fifth nerve, to be distributed 

 to the lateral or external rectus and retractor bulbi muscles 

 of the eye. 



The seventh, ox facial, nerve arises from the medulla, closely 

 behind the fitth, in company with which it leaves the skull 

 after emerging from the prootic ganglion. It soon divides 

 into two branches ; the first, \he palatine, courses along the 

 ventral side of the orbit, just above the mucous membrane 

 of the mouth. At the anterior end of the orbit it gives off 

 a branch which extends laterally and joins the maxillary 

 branch of the fifth nerve. The main nerve passes forward 



