CEREBELLUM. 



515 



From these nuclei, groups of nerve-cells may be traced for a con- 

 siderable distance down the medulla. The relation of the auditory 

 nuclei, and of the sensory nucleus of the fifth, to the grey matter of the 

 medulla, has been already spoken of. In the position of the motor 

 nucleus of the fifth, cells can be traced as far as the point of the 

 calamus scriptorius. From the facial nucleus, a group of cells extends 

 do\vn to the inner side of the hypoglossal nucleus, to the lowest part of 

 which it may be traced. This relation is of considerable interest in 

 connection with the conjoined movements of the lips and tongue. 



(For fuller details on the anatomy of the medulla oblongata and pons 

 Varolii the reader is referred to Lockhart Clarke's paper in the Philo- 

 sophical Transactions for 18G8, to Meynert's article on the Brain in 

 Strieker's Histology, to Henle's Handbuch der Anatomic, Bd. iii., 

 Abth. 2, and to Kulliker's Handbuch der Gewebelehre, 5th ed.) 



THE CEREBELLUM. 



The Ceredellum hinder Irain, consists of a lody and of three pairs of 

 cnira or peduncles, by which it is connected with the rest of the cerebro- 

 spinal axis. 



The cerebellum is covered with grey cortical substance, rather darker 

 than that of the cerebrum. Its greatest diameter is transverse, and 

 extends to about three and a half or four inches : its width from before 

 backwards is about two or two and a half inches ; and its greatest 

 depth is about two inches, but it is much thinner round its outer 

 border. 



Fig. 3G0.— Outline of the Upper Fig. 360, 



Surface OF THE Cerebelluji. (Allen 

 Thomson. ) \ 



At the upper part of the figiu-e, the 

 crura cerebri and ijarts behind them 

 have been cut through and left in con- 

 nection with the cerebellum. 



in. the third pair of nerves lying 

 upon the crura cerebri ; c r, white 

 matter or crust of the crura cerebri ; 

 I n, locus niger ; t, tegmentum contain- 

 ing grey matter in the upper part of 

 the crura ; a s, aqueduct of Sylvius ; 

 q, corpora quadrigemina, the upper 

 elevations di\dded ; s v, superior ver- 

 miform process, some of the foremost 

 folia, immediately behind q, form the 

 central lobe (of Reil) ; I q, lobulus 

 quadratus ; p s, posterior superior lobe ; 



fh, horizontal iissure ; p I, posterior inferior lobe ; n, the notch between the hemi- 

 spheres. 



It consists of two lateral hemispheres joined together by a median 

 portion called the vermiform ^jrocess,. which in man is distinguishable 

 only as a small though well marked part below, named the inferior 

 vermiform process, and a mere elevation above, called the superior 

 vermiform process (fig, 360), In birds, and in animals lower in 

 the scale, this middle part of the cerebellum alone exists ; and in 

 most jnammals it forms a central lobe very distinct from the lateral 

 portions. 



The hemispheres are separated behind by a deep noicU (fig, 360, n). 



L L 2 



