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VETERINARY PHYSIOLOGY 



B. Outgoing (fig. 40, B). From the neurons in the ventral 

 part of the cord, fibres are given off which pass out in the 

 ventral roots of the spinal nerves to muscles, glands, and 

 other reacting structures. 



The fibres entering and leaving the base of the brain by the 

 cranial nerves belong to this arc. 



The action of these neurons is controlled and modified by the 

 two other series of central neurons. 



FIG. 40. To show the three Arcs in the Central Nervous System. A, Peripheral 

 ingoing neuron giving off collaterals in the cord and some terminating 

 above in the nuclei of the dorsal columns ; , peripheral outgoing neurons ; 

 C, ingoing cerebral neurons ; D, outgoing cerebral neurons, crossing to 

 the opposite side at // ; E t ingoing cerebellar neurons ; F, outgoing 

 cerebellar neurons. 



2. Cerebral Arc A. Ingoing (fig. 40, C] (a) Lower 

 Neurons. These are the ingoing neurons of the spinal arc, 

 described above. 



(b] Intermediate Neurons. These start (i.) from the cells in 

 the nuclei of the dorsal columns, and, crossing the middle 

 line, run up to the base of the great brain, where they end in 

 synapses round other cells in the thalamus options (fig. 40, C) ; 

 (ii.) from the cells in the spinal cord with which the spinal 

 ingoing neurons have made synapses. The fibres to the cere- 

 brum cross in the cord and run up to end in synapses in the 

 thalamus; (iii.) from the synapses in the base of the brain, 

 formed by the incoming fibres of the head sense organs. These 

 fibres also pass up to end in the thalamus. 



(c) Upper Neurons. From cells in the thalamus, processes 

 pass up to the cortex of the great brain, to end in synapses 

 with the neurons situated there. 



