INTERNAL STRrCTUEE. 



653 



elongated vertically in front. A thick layer of grey substance occupies 

 its floor, beneath ^yhich, on each side, is the common nucleus of the 

 third and fourth nerves. 



INTERNAL STRUCTURE OP THE CEREBRUM. 



The cerebrum, like the rest of the encephalon, is composed of white 

 and grey substance, the white pervading nearly the whole of its extent, 

 though more exclusively composing its deeper parts ; the grey forming 

 a covering of some thickness over the whole surface of the convolutions, 

 and in certain of the deeper parts either collected into distinct masses 

 or scattered among the bundles of nerve fibres, snch as the corpora 

 striata, thalami optici, corpora quadrigemina, and crura cerebri. To 

 the grey substance, the names of cineritious and cortical have been 

 applied ; to the white that of medullary. 



The White Matter of the encephalon consists of tubular fibres, 

 varying in size in different parts, but in general still smaller than those 

 of tlie cord, their average diameter being the Toooo^h of an inch. 

 Non-medullated fibres are seen only in the neiglibourhood of the 

 grey matter in the basal ganglia and cortex. The fibres of the white 

 substance present no divisions. They are arranged in bundles sepa- 



Ficr. SS6. 



Fig. 38(5. — Sketch op a Dissection shovting the connection of the Columns of the 

 Medulla Oblongata with the Cerebrum and CEREBELLUii (from Mayo). ^ 



In the lower part of the figure the medulla oblongata is entire where it is prolonged 

 downwards into the spinal cord ; a, the anterior pyramid ; a', its continuation upwards 

 into the pons Varolii (•;») ; c, olivary body ; c', olivary fasciculus ; behind c', the fasciculi 

 teretes arc represented ; d, the white laminre in part of the cerebellum ; /, superior 

 peduncle of tlie cerebellum ; g, anterior part or crust of the cerebral peduncle ; h, part 

 of the fibres radiating from the peduncle into tlie right cerebral hemisphere, of which a 

 considerable extent is shown containing parts of the frontal, parietal, and occipital lobes ; 

 ^'i y, y, part of the corona radiata ; K (in front), central fibres of the convolutions ; i, 

 fillet ; I, back of the thalamus opticus ; m, pons Varolii ; n, inferior peduncle of the 

 cms cerebelli ; o, section of the pes hippocampi ; r, tegmentum ; y, y, show the white 

 fibres issuing from the corpus striatam. 



