THE TELENCEPHALON. 



1187 



be conveniently considered under two groups, the short and the long tracts^ accord- 

 ing to the position of the nuclei with which they are associated. 



The short projection tracts include the following : i. T\\e cortico-thalaviic 

 tracts, the fibres of which pass from all parts of the cortex of the hemisphere to the 

 thalamus. The components of these tracts are : (a) fibres passing from the cortex 

 of the frontal lobe to the anterior extremity of the thalamus ; {b) fibres passing from 

 the cortex of the Rolandic region and the adjoining part of the parietal lobe' to the 

 lateral and mesial nuclei of the thalamus ; (c) fibres passing from the occipito-tem- 

 poral lobe to the medio- ventral part of the thalamus ; and {d) fibres passing from the 

 posterior part of the parietal and from the occipital lobe to the pulvinar. 



Associated with the foregfoinsf 

 corticifugal paths are the thalamo- Fig. 1026. 



cortical tracts which, coursing in the 

 opposite direction (corticipetally), 

 proceed by way of the stalks or 

 peduncles of the thalamus (page 

 1 1 22) to all parts of the cortical 

 sheet of gray matter investing the 

 cerebral hemisphere. The thalamo- 

 cortical tracts (Fig. 969), are the 

 continuations (by means of the thala- 

 mic neurones) of the afferent paths 

 conveying impulses from the spinal 

 cord and the brain-stem and from 

 the cerebellum to the great sensory 

 internode, the thalamus. These 

 include, on the one hand, chiefly 

 the median Jillct, the spino-tha- 

 lamic tract and, perhaps, a part of 

 Gowers' tract, by which paths the 

 sensory impulses collected by the 

 spinal and the cranial nerves are 

 transmitted to the thalamus ; and, 

 on the other hand, the cercbello- 

 rjibro-thalamic tracts, by which the 

 cerebellum is linked with the thal- 

 amus by way of the superior cerebel- 

 lar peduncle. The visual impulses 

 carried by the fibres of the optic 

 tract to the pulvinar are, in a similar 

 manner, conveyed to the occipital 

 cortex, along with those interrupted 

 in the lateral geniculate and the 

 superior quadrigeminal body, by the 

 optic radiation of which the occipital 

 stalk of the thalmus is a part. 



2. The cortico-genicidate and 

 the cortico-quadrigcniinal tracts are important constituents of the optic radiation. 

 Their fibres extend from the occipital cortex to the primary optic centres and, as 

 in the case of those going to the pulvinar, are accompanied within the radiation 

 by corticipetal fibres passing from the small lateral geniculate body and the 

 pulvinar. 



3. The auditory radiation comprises both corticipetal and corticifugal fibres 

 which, in proceeding outward, pass from the inferior quadrigeminal and the median 

 geniculate body through the retrolenticular portion of the posterior limit of 

 the internal capsule and beneath the lenticular nucleus 

 within the temporal lobe. This cortical centre includes 

 the superior temporal convolution and, probably, the 

 temporal operculum. 



Cortico-rutjrai 

 Fronto-pontine- 



Temporo- 

 occipito-pontine 



Cerebello-pontine 



Lateral 

 pyramidal 



Direct pyramidal 



Diagram of long projection fibres; nuclei of cranial nerves are 

 indicated by Roman numerals ; R, red nucleus. 



to the auditory centre 

 the middle portion of 

 adjoining part of the 



