740 



DISSECTION OF THE BRAIN. 



Pyramidal 



tract in 

 pons. 



Grey matter 

 in transverse 

 fibres. 



Formatio 

 reticularis. 



Raphe. 



Superior 

 olive. 



oilier, but that they break off near the middle line and mostly 

 assume a longitudinal direction. They are in great part connected 

 with pontine cells which are associated with fibres descending in 

 the crusta of the cms cerebri of the opposite side. 



The pyramidal fibres (fig. 266, 267, pyr. b) enter the pons below as 

 a single mass, but in their passage upwards through the pons they 

 are broken up by decussating bundles of transverse fibres. Much 

 increased in number, they emerge at the upper border of the pons, 

 and are continued into the lower portion (crusta) of the crus cerebri. 



Scattered amongst the transverse fibres are numerous small masses 

 of grey matter (nuclei pontis), with which the cerebellar fibres are 

 connected, as just explained. 



The reticular formation of the pons (fig. 266) is formed of longi- 

 tudinal fibres continued from the medulla oblongata and passing 

 upwards to the upper portion (tegmentum) of the crus cerebri and 

 decussating with various transverse fibres. It contains much in- 

 terspersed grey matter ; and near the floor of the fourth ventricle 

 there are several nerve-nuclei, which will be referred to when that 

 cavity is described. 



In the dorsal portion of the pons, as in the medulla oblongata, 

 there is a median raphe (fig. 267, ra), formed mainly by the trans- 

 verse fibres changing their direction as they cross the middle line. 



There is also in the lower part of the pons, close behind the dee]) 

 transverse fibres of the ventral portion, and occupying a position 

 immediately above the olivary body, a small collection of grey 

 matter to which the name of superior olivary nucleus is given (fig. 267, 

 Son), and which is connected with some of the fibres coming from 

 the cochlear portion of the auditory nerve. 



SECTION IV. 



DISSECTION OF THE CEREBRUM. 



Situation The CEREBRUM, or great brain, the largest of the subdivisions of 

 cerebrum. tne encephalon, fills the upper part of the cranial cavity, and 

 occupies the anterior and middle fossae of the base of the skull. Its 

 hinder part rests on the tentorium, which separates it from the cere- 

 Lower limit bellum. Its lower limit would be indicated on the surface of the, 

 head by a line carried along the eyebrow to the external angular 

 process of the frontal bone and then descending to the upper border 

 of the zygoma and continued backwards to the external occipital 

 protuberance. 



Form. Taking the general form of the cranial cavity, the cerebrum is 



convex on the upper aspect, and uneven on the lower. It consists 



Two hemi- O f two hemispheres, which are placed side by side, and separated by a 



median longitudinal fissure above as far down as the great transverse 



