370 PHYSIOLOGY 



peduncles, which run forward to the posterior corpora quadrigemina. The 

 restiform bodies can be regarded as the direct continuation forwards of the 

 lateral columns of the cord, minus the pyramidal tracts, the chief remaining 

 tract therefore being the posterior or direct cerebellar tract. In the region 

 of the dorsal nuclei, however, it receives accession of fibres from the gracile 

 and cuneate nuclei of the same side and, through the superficial arcuate 

 fibres, from the nuclei of the opposite side, and thus passes as a thick white 

 bundle into the cerebellum. Among these arcuate fibres are also a number 

 derived from the olivary body of the opposite side, known as the cerebello- 

 olivary fibres. On its way it is joined by a smaller bundle, the ' internal 

 restiform body,' which conveys fibres from the vestibular division of the 

 eighth nerve and* also serves to connect Deiters' nucleus with the cerebellum. 

 The restiform body is thus made up of the following fibres (Fig. 184) : 



(1) The direct or posterior cerebellar tract, derived from the cells of 

 Clarke's column on the same side of the cord. 



(2) The posterior superficial arcuate fibres, derived from the gracile and 

 cuneate nuclei of the same side. 



(3) The anterior superficial arcuate fibres, from the gracile and cuneate 

 nuclei of the opposite side. 



(4) The cerebello-olivary fibres. 



(5) The vestibule- cerebellar fibres. 



A section through the pons shows the fourth ventricle widely dilated, 

 with a floor formed of grey matter as in the medulla. The chief difference 

 in the appearance of the section is due to the great masses of transverse 

 fibres which pass into the pons by the lateral peduncles of the cerebellum, 

 cross by the median raphe, and turn either upwards or downwards on the 

 opposite side or end in connection with the nerve-cells which are scattered 

 throughout the white fibres. The pyramids can still be seen as thick longi- 

 tudinal bundles on each side in the midst of the transverse fibres. They are 

 considerably larger than in the medulla and become larger as we trace them 

 up towards the mid-brain, owing to the presence of a number of fibres 

 which are derived from the cortex cerebri and end in the grey matter of the 

 pons. The tract of the fillet lies on each side of the middle line dorsally to 

 the transverse fibres. A little to the outside of the fillet is seen a special 

 mass of grey matter, known as the superior olive. The nervous mass lying 

 behind the transverse fibres of the pons, between them and the grey matter 

 of the floor of the fourth ventricle, is known as the formatio reticularis. It 

 is divided into a lateral and mesial part by the fibres of the hypoglossal 

 nerve. In the lateral portions there is a considerable quantity of grey 

 matter, which can be regarded as continuous with the grey matter of the 

 lateral horns of the cord. The ' lateral nucleus ' is simply a condensed part 

 of this grey matter, lying between the olive and the gelatinous substance of 

 Rolando. The mesial part of the formatio reticularis is almost free of nerve- 

 cells. The reticular appearance of this part of the pons is due to the inter- 

 section of fibres which run longitudinally and transversely. The transverse 

 fibres are a continuation of the deep arcuate fibres. The longitudinal fibres 



