THE NERVOUS SYSTEM 



1363 



terminate in arborizations in the cortex. The fibres, therefore, of 

 which the middle peduncle of the cerebellmn is composed may be 

 regarded as being of two kinds, namely, efferent and afferent. 

 The efferent fibres arise in the cerebellar cortex and terminate 

 in the pons, whilst the afferent fibres arise in the pons and terminate 

 in the cerebellar cortex. 



The bundles of longitudinal fibres in each half of the ventral part 

 of the pons are derived from the breaking up of the crusta or pedal 

 portion of the corresponding crus cerebri, which enters the pons at 

 its upper border. Most of these bundles are collected together at 

 the lower border of the pons, and form the pyramid of the medulla 

 oblongata on the same side. Certain of the fibres of the crusta of the 

 cms cerebri, however, 

 terminate in the pons, 

 as follows: (i) some 

 end in arborizations 

 around the cells of the 

 motor nucleus of the 

 fifth cranial nerve, the 

 nucleus of the sixth 

 cranial nerv^e, and the 

 nucleus of the seventh 

 cranial, or facial, ner\e ; 

 and (2) others end in 

 arborizations around 

 the cells of the nucleus 

 pontis, all of the same 

 side. 



The grey matter of the 

 pons, which is large in 

 amount, occupies the 

 intervals between the 

 intersecting transverse P, Right Pyramid ; O.B., Right Olivary Body, 

 and longitudinal bun- 

 dles, and contains small multipolar nerve-cells. It is kno\vn as the 

 nucleus pontis, and is continuous with the arcuate nuclei of the 

 medulla oblongata. 



Corpus Trapezoides or Trapezium. — ^The trapezium represents a 

 group of transverse fibres, on either side, which have no connection 

 with the corresponding middle peduncle of the cerebellum. The 

 fibres are situated in the lower part of the pons, dorsal to the pjTa- 

 midal bimdles. Within the trapezium are large multipolar cells, 

 which constitute the nucleus of the trapezium. The fibres of the 

 trapezium arise chiefly as the axons of the cells of the ventral 

 cochlear nucleus and also of the lateral cochlear nucleus or tuber- 

 culum acusticum, in which nuclei the fibres of the cochlear di\nsion 

 of the auditory ner\'e terminate. Some of the fibres arise from the 

 superior olivary nucleus; others are the axons of the cells of the 

 nucleus of the trapezium; whilst a third set {strice acusticce) arise 



Corpora Albicantia 



Crusta of Crus Cerebri ___,." \^\Jug 

 Locus Perforatus Postic'jf "" Aiwy 



Right Pyramidal Tract 



Transverse Fibres of 

 Pons Varolii 



Middle Peduncle of 

 Cerebellum 



Decussation of the Pyramids — - — 1, I 



Fig. 570. — Dissection of j.^.^ ^ ,:.s Varolii, 

 showing the course of the pyramidal 

 Tracts of the Medulla Oblongata 



(HiRSCHFELD AND LeVEILL^). 



