THE NERVOUS SYSTEM 



489 



cell-connections are formed all the way along, either by means of 

 collaterals or by the fibres actually terminating ; in either case 

 synapses are formed around the cells in the ventral horns of grey 

 matter. From these axons arise which eventually form the 

 motor root of the spinal nerves. The motor roots pass to the 

 muscles, where they terminate in an end plate. It will be 

 observed that there are two neurone systems in this path, one 



Fig. 147. — Paths from Cortexjin Corona Radiata, Human (Starr). 



A, tract from frontal convolutions to nuclei of pons and so to cerebellum ; 

 B, motor pyramidal tract ; C, afferent tract for tactile sensations (represented 

 in the diagram as separated from B by an interval for the sake of clear- 

 ness) ; D, visual tract ; E, auditory tract ; F, G, H, superior, middle, and 

 inferior cerebellar peduncles ; J , fibres from the auditory nucleus to the 

 posterior corpus quadrigeminum ; K, decussation of the pyramids in the 

 bulb ; FV, fourth ventricle. The Roman numerals indicate the cranial nerves. 



between the cortex and the cord (pons for the facial muscles), 

 the other between the cord and the muscle. From the moment 

 these fibres start on their journey from the cortex, connec- 

 tions are formed with neighbouring structures by means of 

 synapses, not only in the cortex, but mid-brain, pons, bulb, 

 and, as we have seen above, in the cord. It has even been 

 considered that in their passage along the cord the two tracts 

 exchange fibres from opposite sides. In this way is formed the 



