THE OLIVAEY BODT. 315 



Some fibres (commissural) join the root from the raphe, and 

 others seem to arise from the abducens nucleus, though this is 

 denied by many authors. The fibres which seem to arise from 

 the abducens nucleus are probably fibres from the anterior 

 nucleus of the facial, which do not traverse the coil ("genu," 

 as it is called), but enter the root directly. 



The facial root thus formed goes directly outward at first 

 toward the external angle of the fourth ventricle, then turns 

 sharply forward to emerge at the junction of the pons and 

 medulla external to the sixth root. Many authors, first of 

 whom was Clarke, describe an inferior nucleus of the facial 

 nerve, supposing it to innervate the lips and mouth, basing 

 their assertions as much on the seat of lesion in labio-glosso- 

 pharyngeal paralysis as on anatomical evidence. There can 

 be but little doubt as to its existence, and probably it corre- 

 sponds to the group of cells seen in Figs. 137 and 138. 



Sections of the pons above this point soon begin to show 

 traces of the fifth nerve. (See 

 Fig. 143.) The picture we get 

 in transverse sections at the 

 emergence of the fifth root is, 

 in front, two large bundles of 

 longitudinal nerve-fibres sur- 

 rounded by the arciform fibres 

 and separated by the raphe ; 

 behind, the gray matter of the 

 fourth ventricle, which here is 

 pentagonal in shape and is 

 covered in by the base of the , I IG ; i4s.- Dia K rwn showing origin and course 



f of the tngeminus nerve. 



cerebellum, the inferior vermi- 

 form process. Emerging from the gray matter in front of the 

 external corner of the ventricle, and also joined by fibres from 

 above and below, is a large bundle of fibres which pursue a 

 diagonal course outward and forward, to emerge from the side 

 of the pons. This is the sensory root of the fifth nerve. Inter- 

 nal to this root, just after its formation, is seen in successful 

 sections a large group of multipolar cells sending off fibres, the 

 motor root, which join the sensory root and emerge with it. A 

 collection of large, oval, pigmented cells here underlie the exte- 

 rior part of the fourth ventricle and form the locus cceruleus. 

 It seems to have an indistinct connection with the trigeminal 



