378 



PHYSIOLOGY 



probably functionally, part of the cerebral hemispheres, and its connections 

 will therefore be best dealt with when describing the latter bodies. 



THE AXIAL GREY MATTER 



In the spinal cord we could distinguish between the anterior grey matter 

 giving origin to the motor nerves, the posterior grey matter serving as an end 

 station for a number of the sensory posterior root fibres, and a lateral horn, 



DESCENDING 

 ROOT VIII. ' 



1GULA 



'AGUS] 



'ARCUATE 

 NUCLEUS 



r XII. 

 [HYPOGLOSSAL] 



FIG. 191. Cross-section of medulla showing nuclei of nerves x and xn. 

 (CUNNINGHAM.) 



less well marked, probably giving origin to the visceral system of nerves. 

 As the central canal widens out to form the fourth ventricle, the relative 

 position of these various parts becomes altered, the anterior grey matter 

 being now nearest the median line, while the posterior grey matter lies more 

 laterally. Part of the lateral grey matter seems to lie deeper than the rest, 

 from which it is separated by the tangle of fibres and cells known as the 

 formatio reticularis. All the cranial nerves from the third to the twelfth 

 arise or end in the axial grey matter, or in close proximity to it. So great, 

 however, is the complexity of this part of the nervous system, and so in- 

 volved are the genetic relations of the various nerves, that it is difficult or 

 impossible in many cases to state definitely the spinal analogies of these 

 nerves. 



The cranial nuclei (of origin or termination) may be roughly classed as 

 follows : 



(1) Motor Somatic Nuclei. These consist of an almost continuous column 

 of multipolar cells, lying close to the middle line on each side in the floor of 



