CHAP. X.] THE MEDULLA OBLONG ATA. 269 



information sufficiently specific to enable us to make a positive 

 statement respecting the points in question. There is nothing in 

 the results of Stilling's researches which does not confirm that 

 which previous dissections, by coarser means of observation, had 

 pointed out namely, that the restiform and pyramidal bodies are 

 composed in great part of fibres, taking a longitudinal course, 

 while the central portion contains both the vesicular and fibrous 

 nervous elements. The fibres of the latter, according to Stilling, 

 taking chiefly, if not exclusively, a transverse direction. 



There is no evidence of any interchange of fibres between the 

 restiform bodies, nor between the posterior pyramids of the right 

 and left sides, such as has been noticed between the anterior pyra- 

 mids in the description of their decussating fibres. The central or 

 olivary columns of the medulla oblongata, however, have a very in- 

 timate connexion with each other, along the mesial plane, apparently 

 by fibres passing from one to the other. 



When the medulla oblongata is divided vertically along the me- 

 dian plane, a series of fibres is seen to form a septum between its 

 rig-ht and left half. These fibres take a direction from before 

 backwards, and appear to connect themselves with the posterior 

 olivary columns. They are limited inferiorly by the decussating 

 fibres. Cruveilhier proposes for them the name antero-posterior 

 fibres ; they appear to belong to the same system as the arciform 

 fibres. 



Of the Cerebellum. This segment of the encephaloii is situated 

 above and behind the medulla oblongata in a distinct compartment 

 of the cranium, which has for its roof the tentorium cerebelli. It 

 bears to the cerebrum in point of weight about the proportion 1 : 8, 

 and to the entire encephalon, 1 : 10. 



The cerebellum consists of a central and of two lateral portions. 

 The former, also called the median lobe, is the primary part ; it is 

 the only part of the organ which exists in fishes and reptiles ; the 

 lateral portions or hemispheres are additions to this, and denote an 

 advance in development. It is in birds that these are first found; 

 they are most highly developed in mammals, and attain their max- 

 imum in man. 



Upon removing the pia mater from the surface of the cere- 

 bellum, we observe its arrangement in numerous thin lamellae, 

 which are attached to a central column of fibrous matter. A vertical 

 section of either hemispheres serves well to display their structure. 

 A series of planes of fibrous matter become detached from the 

 ('(Mitral white column, each plane separating from it at a different 



