THE CENTRAL NERVOUS SYSTEM 



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to make connection with the motor nuclei of the cranial nerves 

 in the grey matter underlying the aqueduct of Sylvius and the 

 fourth ventricle terminate. Most of these fibres decussate to 

 make physiological connection with nuclei on the opposite side, 

 but some join nuclei on the same side. The question whether 

 they arborize directly around the cells of the motor nuclei or 

 make junction with them through another intercalated neuron 

 is precisely in the same position as the corresponding question 



FIG. 326. PATHS FROM CORTEX IN CORONA RADIATA (STARR). 



A, tract from frontal convolutions to nuclei of pons and so to cerebellum ; 

 B, motor pyramidal tract ; C, afferent tract for tactile sensations (represented 

 in the diagram as separated from B by an interval for the sake of clearness) ; 

 D, visual tract ; E, auditory tract ; F, G, H, superior, middle, and inferior cere- 

 bellar peduncles ; J, fibres from the auditory nucleus to the posterior corpus 

 quadrigeminum ; K, decussation of the pyramids in the bulb ; FV, fourth 

 ventricle. The Roman numerals indicate the cranial nerves. 



for the spinal pyramidal path (p. 775). On their way through 

 the pons they send off collaterals to the nuclei pontis, as they do 

 higher up to the grey matter of the basal ganglia of the cerebrum 

 and the substantia nigra, and the path may be continued to the 

 motor nuclei by axons arising here. There is no proof, however, 

 that this is the case. The rest of the pyramidal fibres run on into 

 the pyramid of the bulb, where the greater part (usually about 

 90 per cent.) of the fibres decussate, appearing in the cervical 



