530 



THE CEREBRUM. 



and prominent, and occupies the middle fossa of the skull the edge of the 

 lesser wing of the sphenoid bone corresponding with the Sylvian fissure. 



Fig. 362. UPPER SUR- 

 FACE OF THE BRAIN 



SHOWING THE CONVO- 

 LUTIONS (from R. Wag- 

 ner). 4 



This view was taken 

 from the brain of a 

 famous mathematician, 

 Professor C. F. Gauss, 

 who died in 1854, aged 

 78. It is selected as 

 an example of a well- 

 formed brain of the 

 usual size with fully 

 developed convolutions. 

 a, superior or first 

 frontal convolution ; a', 

 second or middle frontal ; 

 ", third or inferior 

 frontal ; A, A, anterior 

 ascending parietal con- 

 volution ; B, B, pos- 

 terior ascending parietal 

 convolution ; b, first or 

 upper parietal convolu- 

 tion ; b', second or mid- 

 dle ; b", third or in- 

 ferior ; c, first or upper 

 tempoi'al convolution ; 

 d, first or upper occipi- 

 tal convolution ; d', 

 second or middle ; d", 

 third or lower ; I, I, the 

 superior longitudinal fis- 

 sure ; r, the fissure of Rolando ; p, the external perpendicular fissure. 



The posterior lobe is smooth and slightly concave on its under surface, 

 where it rests on the arch of the tentorium. 



It is right to remark that some anatomical writers have admitted only two lobes, 

 reckoning the middle and posterior lobes as one, under the name of the posterior 

 lobe ; while others more recently have divided the middle lobe into two, an upper 

 and lower, and have added that of the island of Reil, so as to make five principal 

 lobes in all. These have been named respectively the frontal, parietal, temporal, 

 occipital, and central lobes. 



The great longitudinal fissure, seen upon the upper surface of the brain, 

 extends from before backwards throughout its whole length in the median 

 plane, and thus separates the cerebrum, as already stated, into a right and 

 left hemisphere. On opening this fissure, it is seen, both before and behind, 

 to pass quite through to the base of the cerebrum : but in the middle it is 

 interrupted by a large transverse mass of white substance, named the 

 corpus callosum, which connects the two hemispheres together. While the 

 brain is in its natural situation, this fissure is occupied by a vertical process 

 of the dura mater the falx cerebri which dips down between the two 

 hemispheres, not quite reaching to the corpus callosum. 



The Sylvian fissure, which separates the anterior and middle lobes, passes 

 at first upwards and backwards in the outer part of the hemisphere, and 



