802 THE CENTRAL AXIS OF THE NERVOUS SYSTEM. 



Viewed superiorly, it shows the upper part ot the frontal, parietal, and occipital lobes. The 

 frontal lobe is separated from the parietal by the fissure of Rolando, which is very deep and 

 almost transversely intersects the middle portion of the liemisphere. The parietal lobe is 

 separated fDin the occipital by the external perpendicular fissure. 



The fissure of Rolando is separated by two large convolutions — the frontal ascending and 

 parietal nscending. 



The inferior face of the hemisphere is intersected by a deep_/i8«wre of Sylvius, at the bottom 

 of whicli is found the lohde of the insula, when the temporal lobe, situated in front of it, ia 

 separated from the frontal lobe, situated behind it. 



The internal face presents, besides the parts described in animals, two fissures — the internal 

 perpendicular and vertical branch of the calloso -marginal fissure. Between these two fissures 

 is Xhecentral or quadrilateral lobule — a dependency of the parietal lobe ; in front, the paracentral 

 lobule that surrounds the termination of the fissure of Rolando, and the internal face of tlie 

 frontal lobe ; behind, the cuneiform lobule, the internal portion of the occipital lobe. 



Its convolutions are larger, and separated by deeper sulci than in the domestic animals. 



Fig. 448. 



THE BASE OF THK HUMAN BRAIN. 



1, Longitudinal fissure ; 2, anterior lobes of cerebrum ; 3, olfactory bulb ; 4, lamina cinerea ; 5, fis- 

 sure of Sylvius ; 6, locus perforatus auticus ; 7, optic commissure ; 8, tuber cinereum ; 9, third 

 nerve; 10, corpus albicantium ; 11, fourth nerve ; 12, locus perforatus posticus ; 13, fitth nerve; 

 14, crus cerebri; 15, sixth nerve; 16, pons Varolii ; 17, fiortiodura of seventh nerve; 18, middle 

 lobe of cerebrum; 19, portio molliss of seventh nerve; 20, anterior pyramid; 21, glosso-pharya- 

 geal nerve; 22, olivary body; 23, pneumogastric nerve; 24, lateral tract; 25, spinal accessory 

 nerve; 26, digastric lobe; 27, hypoglossal nerve; 28, cerebellum; 29, amygdala; 30, slender 

 lobe ; 32, posterior inferior lobe. 



The frontal convolutions are three in number; the third, or external, indistinct in animals, 

 is situated on the cxterno-iiiftrior part of the lobule, immediately above the fissure of Sylvius; 

 it is named the language convolution, or convolution of Broca, to si>jnify that this surgeon 

 demonstrated that it was the seat of language. These convolutions, all proceeding backwards, 

 pass into the ascending frontal convolution. 



The temporal lobe, which is very developed, shows three undulating convolutions on its 

 smface, distinguished a,s first, second, and third. 



The convolutions of the lobrde of the curved plait are incomparably more developed than in 

 animals. 



Lastly, the occipital lobe has three convolutions— ^rs^ second, and third — ^joined to those of 

 the parietal lobe by two aunectent gyri. 



