856 



THE CENTRAL NERVOUS SYSTEM 



thalamus must be regarded as a great sensory centre through which 

 afferent impulses stream on their way to all parts of the cortex. 



The fibres which connect the cerebral cortex with lower levels of 

 the central nervous system are sometimes grouped together as 

 projection fibres in contradistinction to the commissural and associa- 

 tion fibres. A large proportion of the fibres of the corona radiata are 

 projection fibres, including efferent groups (pyramidal tract, fronto- 



pontine fibres, temporo- 

 pontine fibres) and afferent 

 groups (the fillet system, 

 thalamo-cortical fibres from 

 the grey matter of the 

 thalamus to the cortex, in- 

 cluding the optic radiation). 



SECTION VII. CONNECTIONS 

 OF BRAIN STEM WITH CORD 

 CONNECTIONS OF CERE- 

 BELLUM. 



Connections of the Vestibulo- 

 Spinal or Antero- Lateral De- 

 scending Tract. The main 

 origin of these fibres is the 

 nucleus of Deiters, a collection 

 of large multipolar nerve-cells 

 in the floor of the fourth ven- 

 tricle near the inner auditory 

 nucleus. This nucleus consti- 

 tutes an important intermedi- 

 ate station between the cere- 

 bellum and the cord. Its 

 cells give off axons which pass 

 into the posterior longitudinal 

 bundle of the bulb and pons, 

 mostly to the bundle of the 

 same side, but partly into that 

 of the opposite side. Here the 

 fibres bifurcate into an ascend- 

 ing branch, which passes up to 

 the oculo-motor nucleus, and a 

 descending (vestibulo - spinal] 

 branch, which passes down- 

 wards to the spinal cord and 

 enters the antero -lateral de- 



Fig. 35i. Fibres connecting Frontal and 

 Temporo-Occipital Lobes with Cerebellum, 

 etc. (Diagram) (after Gowers). Fr, frontal, 

 Oc, occipital lobe ; interrupted lines indicate 

 fibres (TOC) connecting cerebellum and 

 temporo-occipital cortex, and fronto-cere- 

 bellar fibres (FC). On left side the position 

 of these two groups of fibres and of motor 

 (pyramidal) tract, PY, in the crus, is indi- 

 cated by letters. The pyramidal tract is 

 seen on the right passing down from the 

 Rolandic area through posterior limb of 

 internal capsule 1C (the genu or knee of 

 which is indicated by asterisk) to decussate 

 in the bulb. AF, ascending frontal convolu- 

 tion; AP, ascending parietal convolution; 

 FR, fissure of Rolando; IFF, intraparietal 

 fissure; PCF, precentral fissure; Ipt, crossed 

 pyramidal, apt, direct pyramidal tract. 



scending tract. The fibres of 



this tract ultimately pass into the anterior horn, where most of them 

 end by arborizing amongst the cells of the horn. Higher up corre- 

 sponding fibres from the posterior longitudinal bundle arborize in the 

 cranial motor nuclei. 



Connections of the Rubro-Spinal Tract. These fibres, as the name 

 given to the bundle implies, originate in the red nucleus and run down 

 into the cord. A little distance from their cells of origin they cross the 



