236 HUMAN PHYSIOLOGY 



called the decussation of the fillet. After crossing, the fibres 

 lie dorsal to the pyramidal tracts ; they then join the sensory 

 fibres which, having perhaps already crossed in the cord, 

 run upward in the lateral bundles. The common sensory 

 tract thus formed, called fillet, passes upward through the 

 pons and the crura cerebri. Thence a part of the fibres go 

 to the ganglia of the corpora quadrigemina ; another part, 

 crossing the ventro-lateral nucleus of the thalamus opticus, 

 pass, always posterior to the pyramidal tract, through the 

 posterior limb of the internal capsule into the corona radiata 

 to the cortex of the cerebral hemispheres. 



In their course the fillets receive fibres originating from 

 masses of cells in which the sensory cranial nerves, after 

 entering the brain, end ; these fibres cross before joining the 

 fillet. 



The nuclei of the motor and sensory cranial nerves lie in the 

 upward prolongation of the gray matter which forms the floor of 

 the fourth ventricle and, above it, the aqueduct of Silvius. The 

 cranial nerves, except the optic and olfactory, are analogous to the 

 spinal nerves. The optic nerve originates from the group of ganglia 

 in the anterior lobe of the corpora quadrigemina and the lateral 

 geniculate body. The olfactory nerve proceeds directly from the 

 cerebral hemispheres. 



2. The direct cerebellar tracts pass through the restiform 

 body [inferior cerebellar peduncle] to the cerebellum, where 

 they end in the gray matter of the worm. Besides this con- 

 nection of the cerebellum with the spinal cord there are 

 other fibres which unite the cerebellum with the cerebral 

 hemispheres. They are : 



(a) Fibres which pass from the anterior and posterior 

 cortex of the cerebral hemispheres through the anterior and 

 posterior limbs of the internal capsule and the crura cerebri 

 to the nuclei of the pons. Thence they proceed backward 

 to the cerebellum through the middle peduncle of the cere- 

 bellum frontal, temporal, and occipital regions being thus 

 joined to the cerebellum. 



(b) Fibres which proceed from the cerebral hemispheres 

 and, with the fillet, pass through the thalamus opticus into- 



