78 



VETERINARY PHYSIOLOGY 



Receptors on the one side, and outgoing neurons ending in 

 Effectors on the other side ; the neurons between them 

 constituting the Conductor mechanism. 



THE NEURAL ARCS. 



A. Arrangement. 



The neural arcs will later have to be studied more in 

 detail. At present a mere outline of their distribution will 

 be given. 



Fig. 33. — To show the three Arcs in the Central Nervous S3'stem. A, Peri- 

 pheral ingoing neuron giving off collaterals in the cord and some 

 terminating above in the nuclei of the posterior columns ; B, peripheral 

 outgoing neurons ; G, ingoing cerebral neurons ; D, outgoing cerebral 

 neurons, crossing to the opposite side //; E, ingoing cerebellar 

 neurons ; F, outgoing cerebellar neurons. 



1. Spinal Arc. — A. Ingoing Neurons (fig. 33, A) — This 

 set of neurons is developed primarily in connection with the 

 surface of the body, but they also start in muscles, joints, 

 and internal organs. They start in dendritic expansions at 

 the periphery, and enter the cord by the dorsal roots of 

 the spinal nerves in the swelling or ganglion upon which the 

 cell of each neuron is situated (see p. 106). In the cord 

 they divide into (a) branches running for a short distance 

 down the cord ; (b) branches running up the spinal cord. 

 From these branches, processes pass forward to form 

 synapses with the neurons in the ventral part of the spinal 

 cord from which the outgoing fibres to the skeletal muscles 



