CHAPTER VIII. 



Correlation Centres and Tracts in the Medulla 

 Oblongata and Pons. 



THE nerve centres and pathways which have been con- 

 sidered so far do not by any means exhaust the list 

 of structures visible in sections of the medulla ob- 

 longata and pons. There are pathways leading to and from 

 both the cerebellum and the higher regions of the brain, and 

 there are structures which serve for correlation of impulses 

 within this region itself. The functional difference between 

 the correlation centres and the sensory nuclei is, however, 

 one of degree rather than of kind, for sensory nuclei usually 

 receive stimuli from several different sources, as do corre- 

 lation nuclei. The only real difference is that the sensory 

 centre receives a great majority of its stimuli from one source, 

 frequently outside the body. 



One of the most conspicuous correlation centres in the 

 brain stem is a prominent mass of gray matter lying in a 

 ventro-medial situation and having a very characteristic 

 appearance in section (Pis. YH., YIII., XXVI.). This is the 

 inferior olivary complex, of which the functional relations 

 are still very imperfectly understood, but which is known to 

 be intimately related with the cerebellum. The mass is 

 divisible into three distinct nuclei, the medial olive {medial 

 accessory olivary nucletis), the dorsal olive {dorsal accessory 

 olivary nucleus), and the ventro-lateral or principal olive {in- 

 ferior olivary nucleus, oliva inferior), which are continuous with 

 each other at certain points. Each of these is an elongated 

 lamella of rather irregular outline, so that its exact form and 

 position vary at different levels. The medial nucleus extends 



