102 LECTURE IV. 



call them, rests upon the roof of the orbits, whilst the lower 

 or temporal lobes fill up a deep cavity formed by the sphenoid 

 and temporal bones in the base of the cranium, on both sides 

 of the sella Turcica. Again, on viewing the human brain 

 from below, the posterior margin of the hemisphere is seen 

 to project beyond the cerebellum, thus forming a prolongation 

 which is called the posterior lobe. Finally, there may, in this 

 posterior lobe be distinguished a middle or parietal lobe which 

 is, however, the least marked of all. 



Fig. 31. Brain of the celebrated mathematician. Gauss, side view, 



after Waerner. 



8. Sylvian fissure. R. Fissure of Eolando. C. Cerebellum. F. Frontal 

 lobe. P. Parietal lobe. 0. Posterior lobe. T. Temporal lobe of cerebrum. 



On viewing the brain from the side, the deep fissure which 

 separates the temporal from the frontal lobe is seen to divide 

 into two branches, one of which, rising almost perpendicularly, 

 is gradually lost in the mass of the frontal lobe ; the other takes 

 at first a horizontal direction, and is lost between the convolu- 

 tions in the mass of the temporal lobe. This fissure, termed 

 the Sylvian, is important, because, imder all circumstances, it 

 clearly indicates the division between the frontal and the pari- 

 etal lobes. Viewed from above, the brain seems to consist of 

 three parts : the anterior, the parietal, and the posterior lobes. 

 Viewed from the side, there would be added the temporal lobe, 

 and a small concealed lobe, called the island or the central lobe, 



