826 MAN 



tant systems of conduction fibers. The mesial and more massive is the su]3erior 

 cerebellar pechmcle (Sep) in the form of a crescent whose niferior tip 

 is approaching the median hne. Lateral to the superior cerebellar peduncle 

 is the lateral (lllet (Lf), the secondary pathway in the conduction of audi- 

 tory inijiidses. These fibers are approaching a relay station in the inferior 

 colliculus whose ele\'ations are not as yet present at this level. The relative 

 size of the superior cerebellar peduncle is readily appreciated and again 

 affords an opportunity for estimating the volume of efferent impulses pass- 

 ing out of the cerebelfum in connection with the function of muscular coor- 

 dination. The significance of its augmentation has already been discussed 

 and is undoubtedly connected with the vastly increased capacities on the 

 part of man for the liner adjustment in those highly skilled performances 

 whicli require the finest eoordinative control. 



The boundary line between the tegmentum and basis in this section is 

 created by the presence of the transversely disposed bundle of fibers of tlie 

 mesiat fillet (Mf). In the basis are all of the elements characteristic of 

 the pons Varolii, including its three major strata, the stratum superficiale 

 pontis, the stratum complexum pontis, containing the large masses of pontile 

 nuclei, and the stratum profundum pontis. The reticular lormation ( Rel) 

 at tliis level apj;)ears to be reasserting itself as a more extensive structure. 

 At the same time it appears somewhat more dill use, due to the tendency 

 of the superior cerebellar peduncle to undergo decussation. The iormatio 

 reticularis contains no specialized groups of cells at this level, i^ordering 

 upon it and perhaps forming a portion of it is a small aggregation of gray 

 matter, the caudal pole of the substantia nigra. This latter structure has been 

 variously interpreted as to its functional signilicance. At the present time the 

 majority of authorities ascribe to it the regulation of certain automatic 

 associated movements. 



