84 D. A. RHINEHART 



MOTOR PART OF THE NERVUS FACIALIS 



The nucleus of origin and the central course and relations of 

 the motor part of the nervus facialis of the mouse are very simi- 

 lar to those of other mammals and man. The nucleus is located 

 in the ventral part of the pons close to its surface, and just me- 

 dial and slightly ventral to the nucleus olivaris superior. This 

 superficial position is due to the absence of transversely directed 

 pontine fibers other than those of the trapezoid body. 



The nucleus is composed of large multipolar cells closely re- 

 sembling in size and shape those in the oculomotor and hypo- 

 glossal nuclei. Coarse fibers arise from the cells of the nucleus 

 and pass dorsally with a slight inclination medially, scattered 

 over a considerable area of the formatio reticularis. In relation 

 to the dorsal surface of the nucleus abducens the fibers unite into 

 a compact bundle. This bundle passes anteriorly for a short 

 distance and bends at an angle forming the genu internum. 



The emerging part of the nerve passes ventrally, laterally, and 

 slightly anteriorly until near the ventral surface of the pons. 

 Here it makes a bend and emerges from the pons by passing 

 almost horizontaly laterally through the fibers from the cochlear 

 nuclei and between the nucleus and radix spinalis nervi tri- 

 gemini on its dorsal side, and the anterior extremity of the nu- 

 cleus olivaris superior on its ventral side. 



After emerging from the pons the facial nerve passes laterally, 

 dorsal to the cochlea and the tensor tympani muscle, to the dor- 

 sal wall of the tympanic cavity where it bends posteriorly in the 

 genu externum. At the surface of the pons the nerve is in rela- 

 tion to the emerging trigeminal nerve anteriorly, the vestibular 

 nerve and ganglion dorsally, and the cochlear nerve posteriorly 

 (fig. 1). The relation to the vestibular ganglion at this place is 

 accounted for by the fact that it is located against the surface 

 of the pons, anterior and inferior to the ventral cochlear nucleus, 

 and overlapping a part of it. 



Dorsal to the facial nerve between the pons and the genu ex- 

 ternum, are the vestibular nerve and ganglion, the nervus inter- 

 medins, and the ramus ampullae superior and ramus ampullae 



