140 NEKVOUS SYSTEM. 



viding it at its origin or in different portions of its course. 

 In treating of these nerves, we shall first, as in the case of 

 the motor nerves of the eye, study their properties at their 

 roots, noting the phenomena following their galvanization 

 and section. It will be necessary, also, to describe their ori- 

 gin and distribution, as far as has been ascertained by dissec- 

 tion. 



Nerve of Mastication (the Small, or Motor Root of the 



Fifth). 



The motor root of the fifth nerve is entirely distinct from 

 its sensitive portion, until it emerges from the cranial cavity 

 by the foramen ovale. It is then closely united with the 

 inferior maxillary branch of the large root ; but at its origin 

 it has been shown to be motor, and its section in the cranial 

 cavity has demonstrated its distribution to a particular set 

 of muscles. 



Physiological Anatomy. The apparent origin of the 

 fifth nerve is from the lateral portion of the pons Varolii. 

 The small, or motor root arises from a point a little higher 

 and nearer the median line than the large root, from which 

 it is separated by a few fibres of the white substance of the 

 pons. The most satisfactory investigations with regard to 

 the deep origin of the small root are those of Yulpian. Ac- 

 cording to this observer, the dissections should be made after 

 the specimen has been kept in alcohol for about fifteen days, 

 and before the parts are thoroughly hardened. At the point 

 of apparent origin, the small root presents "from six to eight 

 rounded filaments. If a thin layer of the pons covering 

 these filaments be removed, the roots will be found pene- 

 trating its substance, becoming flattened, passing under the 

 superior peduncles of the cerebellum, and going to the ante- 

 rior wall of the fourth ventricle. At this* point, they change 

 their direction, passing now from without inward, and from 

 behind forward toward the median line, the fibres diverging 



