156 



ELEMENTS OF HISTOLOGY. [Chnp. xvm. 



the most anterior bundles-^-of the transverse fibres. 

 The bundles of the pyramidal tract pass as longitudinal 

 fibres merely through the anterior half of the pons, 

 and enter the crura cerebri where they form the 

 crusta. (2) The raphe. (3) The reticular formation; 

 but this is limited to the posterior part. Small masses 

 of grey matter and ganglion cells are scattered every- 

 where between the transverse bundles of the nerve- 

 fibres of this formation. (4) The grey matter at the 

 floor of the fourth ventricle. This grey matter con- 

 tains also on the posterior surface of the pons groups 

 of multipolar ganglion cells. 



Near the middle line there is a group of large 

 multipolar ganglion cells, each with an axis cylinder 

 process. This is the nucleus for the sixth nerve, and 

 of part of the seventh, the former lying more median 

 than the latter. There is another nucleus of the 

 seventh situated more deeply i.e., in the reticular 

 formation. More outwards we meet with the superior 

 nucleus of one of the roots of the auditory nerve. 

 Farther upwards we meet with the nucleus of the 

 motor roots of the fifth. 



(5) In the lower part of the pons there exists also 

 a continuation of the grey matter of the corpus den- 

 tatum of the olivary body. 



205. The pons is connected with the cerebrum by 

 the crusta of the crus cerebri, which, as mentioned 

 above, are bundles of medullated nerve-fibres passing 

 merely through the pons but being continuations of 

 the anterior pyramidal tracts of the medulla. 



206. III. The hemispheres of the cere- 

 brum. On a vertical section each convolution shows 

 a white centre and a grey cortex. The former is com- 

 posed of medullated nerve-fibres. The white matter 

 of the convolutions of the cerebral hemispheres is ar- 

 ranged as (a) the centrum ovale i.e., the central mass 

 of white matter from which the lamina of white matter 



