480 



PHYSIOLOGY 



fibres entering by the posterior root at the level of the cord where 

 they end. 



(2) THE FRONTO-PONTINE FIBRES. These arise from cells in the 

 cortex of the frontal lobe, and pass down in the anterior limb of the 

 internal capsule to gain the mesial part of the crusta of the crus cerebri. 

 The fibres end in the grey matter of the formatio reticularis of the 

 pons, the nucleus pontis. 



(3) THE TEMPO RO-PONTINE FIBRES. These arise from the two 

 upper temporal convolutions, especially from that area which is 

 associated with hearing. They pass inwards under the lenticular 

 nucleus through the hinder limb of the internal capsule to gain the 



outer part of the crusta. In this situa- 

 tion this tract passes down into the pons, 

 where it ends in the nucleus pontis. 



As part of these projection fibres we 

 ought probably to reckon the fibres which 

 take origin or end in the corpus striatum. 

 The afferent fibres of this body are de- 

 rived chiefly from the thalamus, forming 

 the thalamo-striate fibres. Other fibres 

 arise in the nuclei of the corpus striatum 

 and pass down in the dorsal portion of 

 the crusta to end for the most part in 

 the pons, the strio-pontine fibres. 



The relative position of these various 

 fibres in the internal capsule and in the 

 crusta is shown in the accompanying 

 diagrams (Figs. 214 and 215). 



The fronto-pontine and temporo-pon- 

 tine fibres, which end in the nucleus pontis, 

 come there in relationship with the fibres 



forming the middle peduncles of the cerebellum and derived chiefly 

 from the lateral lobes of the cerebellum. These fibres may therefore 

 be regarded as the efferent side of the great cerebro- cerebellar connec- 

 tions of which the afferent side is represented by the fibres efferent 

 so far as concerns the cerebellum which pass from the cerebellar 

 cortex to the dentate nucleus and thence by a fresh relay in the superior 

 cerebellar peduncles to the red nucleus, optic thalamus, and cortex of the 

 opposite side. The development of these fibres, as of the lateral 

 lobes of the cerebellum, is largely proportional to the growth of the 

 cerebral hemispheres. In cases where there has been congenital 

 atrophy of one cerebral hemisphere the crusta of the same side and 

 the lateral lobe of the cerebellum of the opposite side also fail to 

 develop. 



ill 



FIG. 215. Transverse section 

 through mid- brain to show 

 position of fillet and pyramid. 

 AQ, anterior corpus quadri- 

 geminum ; dV, descending root 

 of fifth nerve ; F, fillet (I, lateral, 

 and m, mesial fillet) ; Pyr, pyra- 

 mid ; Fr, fibres from frontal lobe 

 to pons ; TO, fibres from occipi- 

 tal lobe to pons ; Ne, fibres from 

 nucleus caudatus to pons ; III, 

 root of third nerve ; S, Sylvian 

 iter ; Rn, red nucleus. 



