984 THE FIBRES OF THE BRAIN. [BOOK in. 



Corpus dentatum of tlie cerebellum. In the midst of the mass 

 of white matter which is formed in the interior of the cerebellum by 

 the confluence of the three peduncles, is found (Fig. Ill, GD) an 

 area of grey matter arranged, like the olivary body of the bulb, as 

 a sharply folded or plaited band in the shape of a flask or bowl. 

 As in the similar olivary body the grey wall of the flask is 

 covered up by and its interior filled up with white matter; 

 the mouth of the flask is, on each side, directed towards the 

 median line; the fibres pass chiefly to the superior peduncle. 



There are also other collections of grey matter in the central 

 white matter of the cerebellum, one of which, called the " nucleus 

 of the roof," is connected with the two inferior peduncles. 



The Arrangement of the Fibres ,of the Brain. 



631. The systems, tracts and bundles of fibres in which the 

 white matter of the brain is arranged, may be distinguished from 

 each other, partly through mere mechanical separation by means 

 of the scalpel, partly by being traced out with the help of the 

 microscope, but, as in the spinal cord, much more fully and 

 completely by differences of development, and by the method of 

 degeneration. 



We have seen that a marked feature of the brain is presented 

 by the two crura cerebri which, running forward from the hind 

 parts of the brain, spread out into each cerebral hemisphere. 

 We have also seen that the crus in the wide sense of the word 

 consists of two parts, a dorsal part, the tegmentum, and a ventral 

 part, the pes or crusta, and that these two parts differ very strik- 

 ingly from each other in structure and in relations. The pes 

 consists exclusively of bundles of longitudinal fibres, and we may 

 trace these from the cerebral hemispheres into the pons and some 

 of them beyond the pons into the bulb and spinal cord. The teg- 

 mentum is more complex in structure ; it consists of grey matter, 

 and of fibres and bundles of fibres having various relations, both 

 with the collections of grey matter lying within itself and with 

 surrounding structures. It too has connections with the parts 

 lying in front of it, and with the parts lying behind it ; we may 

 trace it too backwards through the pons into the bulb and forwards 

 to the optic thalamus. If we allow ourselves to conceive of the 

 optic thalamus as constituting the front ending of the tegmentum, 

 we may arrange a large part of the brain into two main regions, 

 into a tegmental region stretching from the optic thalamus through 

 the dorsal portion of the pons to the dorsal portion of the bulb, 

 and into a region, which we may call the pedal region, stretching 

 from the internal capsule through the ventral portion of the pons 

 to the ventral portion of the bulb. 



