NEUKO-MUSCULAK MECHANISM 89 



B. Outgoing (fig. 40, D). The outgoing neurons start in the 

 cells of the cortex cerebri, and pass down to the upper part 

 of the spinal cord, where most of them cross and run down 

 the lateral column of the spinal cord, giving off collaterals 

 which end in synapses round the cells in the ventral horn 

 of grey matter, from which the spinal outgoing neurons pass 

 to the muscles, etc. Those which do not cross run down the 

 ventral column of the cord for some distance, and end by 

 crossing and becoming associated with the cells in the ventral 

 horn. 



3. Cerebellar Are A. Ingoing (fig. 40, E). Some of the 

 collaterals of the spinal ingoing neurons end in synapses round 

 a mass of nerve cells at the side of the grey matter of the spinal 

 cord the cells of Lockhart-Clarke. From these cells, fibres 

 extend up at the margin of the cord to the lesser brain or cere- 

 bellum to form, directly or indirectly, synapses round the cells 

 in this organ. From the same group of cells other fibres cross to 

 the opposite side and run up to the cerebellum. Fibres from the 

 synapses, formed by the incoming fibres from the labyrinth of 

 the ear and probably from the eye, also course to the cerebellum. 



B. Outgoing (fig. 40, F). From neurons near the surface of 

 the cerebellum and in the central nuclei axons extend (a) to the 

 medulla oblongata, where they end in synapses round a mass 

 of cells the nucleus of Deiters. From these cells, fibres extend 

 down the lateral columns of the same side of the spinal cord, 

 and give off collaterals to the cells of the ventral horn of grey 

 matter. (6) To the cerebrum. 



The nervous system may thus be considered as built up of 

 these three ares. 



1st. The Spinal arcs consist of the peripheral ingoing neurons 

 and the peripheral outgoing neurons. These arcs exist not 

 only at the level of the cord at which the ingoing neuron 

 enters, but are placed at various levels above and below this 

 point (fig. 40). 



2nd. The Cerebral arcs consist of (1) the peripheral ; (2) 

 the intermediate ; and (3) the upper ingoing neurons ; (4) the 

 central outgoing neurons; and (5) the peripheral outgoing 

 neurons. 



