358 NERVOUS SYSTEM. 



inches or more. The convolutions proceed in diversified and 

 complicated courses, which never correspond in different indi- 

 viduals, and seldom on the two hemispheres of the same brain. 

 Though their summit is generally convex, yet some of them 

 have it depressed slightly, which is considered a proof of each 

 convolution being divisible into two halves or layers, placed side 

 by side. Some of the convolutions are short, others long; they 

 present numerous varieties.in the manner of joining each other. 

 Owing to the narrowness of the fissures between them, they are 

 closely packed together, so that the lateral surfaces of each one 

 are suited to such as are contiguous: occasionally, there is a 

 departure from this rule. 



The surface of the convolution, by which we mean not only 

 the most exterior periphery of the cerebrum, but also the surface 

 formed by the fissures to their very bottom, is covered by cine- 

 ritious neurine or matter of about one line in thickness. 



Within the periphery of the cerebrum, the mass of medullary 

 neurine or matter is very considerable, and is of an ovoidal 

 shape. This ovoid is called the Centrum Ovale of Vieussens, 

 and is brought fairly into view by making a horizontal cut 

 through the hemispheres, two inches below their summit. 



In proceeding with the anatomy of the cerebrum from its 

 base upwards, the following is the order or succession of parts 

 in its structure: In advance of the pons varolii, and springing 

 from it, there are two divergent medullary trunks, one on each 

 side, which run forwards, and are lost in the medullary sub- 

 stance of the cerebrum. These trunks are the crura cerebri, 

 upon the upper surface of each are two protuberances: the pos- 

 terior is the thalamus nervi optici, and the anterior is the cor- 

 pus striatum. Each crus cerebri, having penetrated into the 

 substance of its respective hemisphere, expands by a multipli- 

 cation of the filaments composing it, so as to constitute the prin- 

 cipal bulk of the hemisphere. These filaments may, indeed, be 

 traced very satisfactorily in almost every direction towards the 

 periphery of the cerebrum, where they terminate in the convo- 

 lutions, their extremities being covered by the cineritious mat- 

 ter there. The arrangement is best seen by scraping with a 

 knife along the base of the brain, especially when the latter has 



