90 



PSYCHOBIOLOGY 



the ophthalmic, the superior maxillary, and the inferior maxillary (or 

 mandibular) nerves. The first two are purely afferent, the third mixed. 



The efferent fibers of the trigeminal nerve are derived principally from 

 a nucleus lying at the level of the upper portion of the fourth ventricle. 

 The afferent fibers originate in the Gasserian {semilunar) ganglion, outside 

 of the brain stem; and after entering, divide, one branch ascending to 



re-n 



r ^ 



OPTIC CHIASMA 



Fig. 73. Diagram of the central connections of the optic nerve and optic tract. 

 (Cunningham, Anatomy.) 



a nucleus located laterally and ventrally to the motor nucleus, and the 

 other branch descending as far as the fourth cervical segment of the cord, 

 and terminating among the cells of the substantia gelatinosa Rolandi. 



The distal distribution of the efferent fibers is to the muscles of mastica- 

 tion (the masseter, temporal, and two pterygoid muscles), the mylo-hyoid 

 muscle, the superior belly of the digastric muscle, and the tensor tympani 



