Visceral Afferent System 43 



medial to this and directly under the floor of the fourth 

 ventricle. Some of the fibres of the fasciculus solitarius end 

 in these nuclei/ but many of them descend to about the level 

 of the decussation of the pyramids, where they decussate in 

 a mass of gray matter dorsal to the central canal and con- 

 tinuous with the nuclei of the fasciculi solitarii of the two 

 sides. This mass is the commissural micleus of Cajal {nucleus 

 commissuralis, PI. \'I.), in which the fibres terminate after 

 decussating within it, forming the commissura infima. The 

 commissura infima is not ordinarily seen in Weigert prepara- 

 tions as it contains very few myelinated fibres. A few of the 

 fibres do not decussate, but run right into the upper part of 

 the spinal cord on the same side. 



While the fasciculus solitarius and its gray matter are usually con- 

 sidered to contain both the general visceral and the gustatory connections, 

 there is some evidence in favour of the view that only the former com- 

 ponents end in this way. According to the supporters of this inter- 

 pretation, a considerable proportion of the visceral afferent fibres, at least 

 from nerves IX and X, do not end in the centres mentioned, and chiefly 

 on comparative grounds, these are believed to be the gustatory elements. 

 The nuclei with which they come into relation are two in number on each 

 side, and lie at the level of the entering nerve roots. The larger and 

 more distinct is a small-celled nucleus which is wedged in between the 

 anterior end of the hypoglossal nucleus and the dorsal motor vagus nucleus 

 (p. 47), and is named the nucleus intercalatus of Staderini (PI. VIII.). 

 This nucleus extends medially, forming a cap over the anterior extremity 

 of the hypoglossal nucleus, and becoming continuous with a small mass 

 next to the median line, the nucleus funiculi teretis. In front of the 

 hypoglossal nucleus, it enlarges and occupies the position of the latter for 

 a short distance. It also connects laterally, dorsal to the motor X nucleus, 

 with the second centre to which gustatory functions are attributed, viz., 

 a small mass which forms the ventro-medial angle of the chief vestibular 

 nucleus, and which has usually been considered as part of that centre. 

 Allen, however, could trace no visceral afferent fibres to either of these 

 centres in the guinea pig, but found them all to enter the fasciculus soli- 

 tarius. 



Wlen found no terminals from the tractus solitarius in the nucleus 

 para solitarius of the guinea pig (Jour. Comp. Neur., vol. 35). 



