THE STRUCTURE OF THE BRAIN STEM 



377 



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 



FIG. 192. Diagram showing the brain connections of the vagus, glosso-pharyngeal, 

 auditory, facial, abducent, and trigeminal nerves. (CUNNINGHAM after OBBE- 



STEINBR.) 



ipossible 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 

 the fourth ventricle, the Sylvian iter, and the back part of the third ventricle. 

 From below upwards these groups of cells give origin to the fibres of : 



