THE NERVOUS SYSTEM. 423 



bundles; one of which, ascending in a tolerably straight direc- 

 tion, is continuous with the fasciculus lateralis of the restiform 

 body, and with it enters for the most part into the peduncle of 

 the cerebellum, and in small part into the tegmentum ; a second 

 division penetrates forwards between the divergent anterior 

 columns, decussates in two or three fasciculi with that of the 

 other side (decussatio pyramiduni), constituting the principal 

 bulk of the pyramids; a third division, lastly, appears between 

 the posterior columns at the bottom of the rhomboid fossa, or 

 fourth ventricle, as the eminentia teres. These latter are con- 

 tinued, on the floor of the fourth ventricle and applied to each 

 other, into the tegmentum of the cerebral peduncles, whilst the 

 pyramids, passing between the first and second transverse layers 

 of fibres of the pons, are continued into the base of the cere- 

 bral peduncles. The posterior columns of the cord, lastly, 

 chiefly constitute the fascicidi graciles and cuneati, the latter 

 of which, in great part, enter the pedunculi cerebelli, whilst the 

 remainder, and the fasciculi graciles, situated externally to the 

 eminentia teretes, may be traced into the tegmentum of the 

 crura cerebri. All these fasciculi consist, besides the grey 

 substance, of parallel nerve-fibres of the same dimensions as 

 those of the cord, that is to say, from 0001 — 0001'", seldom 

 more. 



Besides this white substance, the pons Varolii and medulla 

 oblongata, omitting the roots of the nerves, present a system 

 of mostly horizontal fibres. This system consists : 1. of the 

 well-known transverse, arcuate fibres, external to the corpora 

 pyramidalia and olivaria; 2. of straight fibres, which extend 

 from before backwards, in the middle, through the medulla 

 oblongata, contributing to the formation of the so-termed 

 raphe (Stilling); 3. and lastly, of very numerous fibres pro 

 ceeding from this raphe into the lateral halves of the medulla, 

 following a more or less curved direction. These latter, the 

 internal transverse fibres, commence behind the pyramids, and 

 the anterior of them as a large mass, very minutely broken 

 Tip by fine flattened fasciculi of the pyramidal and olivary 

 columns, penetrate from within into the corpus dentatum olives, 

 the white substance of which is constituted by them ; they 

 then expand in a brush-like form, and are continued through 

 the grey substance of the corpus dentatum, ultimately turning 



