600 



HANDBOOK: OP PHYSIOLOGY. 



fibres from the cord as low as the second cervical nerve, and this forms 

 a tract at the tip of the posterior cornu, between it and the restiform 

 body. No nerve cells are connected with it. The roots can be traced 

 obliquely through the pons Varolii, beneath the floor of the front part 

 of the fourth ventricle. The motor root is in a position median to 

 sensory. The nerve appears at the ventral surface of the pons near its 

 front edge, at some distance from the middle line. 



Function. The first and second divisions of the nerve, which arise 

 wholly from the larger root, are purely sensory. The third division 

 being joined, as before said, by the motor root of the nerve, is of course 

 both motor and sensory. 



(a.) Motor. Through branches of the lesser or non-ganglionic por- 

 tion of the fifth, the muscles of mastication, namely, the temporal, mas- 

 seter, two pterygoid, anterior part of the digastric, and mylohyoid, 

 derive their motor nerves. Filaments are also supplied to the tensor 

 tympani and tensor palati. The motor function of these branches is 

 proved by the violent contraction of all the muscles of mastication in 

 experimental irritation of the third or inferior maxillary division of the 

 nerve; by paralysis of the same muscle, when it is divided or disorgan- 



Fig. 366. Section across the pons, about the middle of the fourth ventricle, py. , pyramidal 



r ^i 'f * * ) -VO UU.VsJ.^U.0 , Y JLJL. , J-CH-/1CH 14 d V C , Y J.4. I*. , ill' 



termediate portion, n. VII. , its nucleus; VIII., auditory nerve, nVIIL, lateral nucleus of the 

 auditory. (After Quain.) 



ized, or from any reason deprived of power ; and by the retention of the 

 power of these muscles, when all those supplied by the facial nerve lose 

 their power through paralysis of that nerve. The last instance proves 

 best, that though the buccinator muscle gives passage to, and receives 



