682 



THE NERVOUS SYSTEM. 



the tegmental portion, as most of its constituents are continued into the tegmentum 

 of the crus cerebri. 



The anterior or ventral part consists of three layers of fibres: 1. superficial 

 transverse fibres ; 2. longitudinal fibres ; 3. deep transverse fibres. These three 

 layers are not, however, completely differentiated from each other, for some 

 transverse fibres may be seen between the bundles of the longitudinal fibres 

 (Fig. 362). 



1. The superficial transverse fibres, consisting of a rather thick layer on the 

 ventral surface of the pons, cross the middle line, and proceeding laterally are 

 collected into a large rounded bundle of fibres on each side. This bundle, with 

 the addition of some transverse fibres from the deeper part of the pons, forms the 

 middle peduncle of the cerebellum of the corresponding side. 



2. The longitudinal fibres enter the pons below as a single mass, which forms 

 the continuation upward of the fibres of the pyramids of the medulla ; as they 

 ascend they become broken up into bundles by some of the transverse fibres, and 



Superficial 

 fibres of pons 

 reflected. 



FIG. 362. Superficial dissection of the medulla oblongata and pons. (Ellis.) 



are continued into the crusta of the mid-brain. They lie on either side of the 

 middle line, and cause a bulging of the superficial transverse fibres on the ventral 

 surface of the pons, with a longitudinal mesial groove between them. This is the 

 groove, mentioned above, in which the basilar artery is received. As the fibres 

 ascend they are increased in number, being reinforced by others derived from the 

 nerve-cells in the deep transverse strata. 



3. The deep transverse fibres form a thicker layer than the superficial set, and 

 there is much gray matter between them. The fibres pass from the middle line, 

 where they interlace with those from the opposite side, and, coursing to the lateral 

 borders of the pons, they, for the most part, curve dorsally, and assist the super- 

 ficial transverse fibres in forming the middle peduncle of the cerebellum. Some 

 of the fibres join the nerve-cells which are situated in the gray matter of this 

 layer, and in addition nerve-fibres derived from others of these cells pass off to 

 join the longitudinal fibres (see above). 



