NERVE 79 



spring. It is probable that several series of intei^calated 

 neurons exist between the ingoing and outgoing neurons. 



B. Outgoing Neurons (fig. 33, B). — {a) From the nerve 

 cells in the ventral part of the grey matter of the cord, fibres 

 are given o^ which pass out in the anterior or ventral roots of 

 the spinal nerves to skeletal muscles, and (6) from cells 

 situated in the lateral part of the grey matter of the cord 

 fibres pass out to be connected with the visceral neurons 

 which pass to muscles or to glands (p. 54). 



The fibres entering and leaving the base of the brain by 

 the cranial nerves belong to this spinal arc. 



The action of these spinal neurons is controlled and 

 modified by the two other arcs. 



2. Cerebral Arc— A. Ingoing Neurons (fig. 33, C). 



Loiver Xeurons. — The ingoing fibres of the spinal cord and 

 cranial nerves not only give off branches to form the spinal 

 arcs, but they also form other synapses in or just above the 

 cord from which fresh neurons run upwards, cross the middle 

 line to the opposite side, and finally form synapses higher up 

 and chiefly in the thalamus (fig. 101). From these fibres 

 pass (a) to other basal ganglia such as the red nucleus, and (6) 

 to the cortex cerebri to form synapses. From these fibres 

 pass to the outgoing neurons. 



B. Outgoing Neurons — These cross the middle line and run 

 down the spinal cord to act upon the spinal arcs (fig. 33, B). 



3. Cerebellar Arc— A. Ingoing (fig. 33, E).—{a) Some 

 of the branches of the spinal ingoing neurons from muscles 

 and joints end in synapses round nerve cells at the side of 

 the grey matter of the spinal cord. From these, fibres run up 

 to the cerebellum to form, directly or indirectly, synapses 

 round the cells in this orgfan. 



(6) Fibres from the synapses, formed by the incomino' 

 fibres from the vestibular part of the labyrinth of the ear, 

 also course to the cerebellum. 



B. Outgoing (fig. 33, F). — From the cells of the cortex of 



the cerebellum (a) fibres pass to masses of grey matter the 



roof nuclei — and to a mass of cells lying outside the 

 cerebellum on each side — Deiters' nucleus — where they form 



