EXTERXAL SURFACE. 



529 



fissure, and passes into the ano-ular gyi-us above the extremity of the 

 fissure of Sylvius, except in the rare instances in which the Sylvian 

 fissure is prolonged into the intra-parietal sulcus. 



Fig. 372.— IJprER ScK- Fig. 372. 



FACE OF THE BrAIN 

 SHOWING THE CONVO- 

 LUTIONS (from E. 

 AVagner). h 



Tliis view was taken 

 from the bi'ain of a 

 famous mathematician, 

 Professor C. F. Gauss, 

 who died in 1854, aged 

 78. It is selected as 

 an example of a weil- 

 formed brain of the 

 average size with fully 

 developed convolutions. 



a, superior or fir.st 

 frontal convolution ; a', 

 second or middle frontal ; 

 ft", third or inferior 

 frontal ; A, A, ascend- 

 ing frontal convolution ; 

 B, B, ascending parietal 

 convolution ; b, supe- 

 rior parietal lobule ; 6", 

 inferior parietal lobule ; 



c, first oi- upi^er temporo- 

 sphenoidal convolution ; 



d, first or uj^per occipi- 

 tal convolution ; d', 

 second or middle ; d", 

 third or lower ; I, I, the 

 superior longitudinal fis- 

 sure ; r, the fissure of 



Rolando ; j), the external parieto-occipital fissure (which appears, in consequence of the 

 j)osition of the brain, nearer than it really is to the posterior extremity). 



The cmgnIargjY\is,{ang.c.) is bounded in front by the terminal ascending 

 portion of the fissure of Sylvius, above by the intra-parietal sulcus, below 

 it is continuous with the superior (and sometimes with the middle) 

 temporo-sphenoidal convolution, and behind with the occipital lobe by 

 means of one or two (second and third) annectant convolutions. 



The Occipital Lobe (fig. 370) lies behind the parietal, and forms 

 the posterior extremity of the hemisphere. Below, it is continuous with 

 the temporo-sphenoidal lobe. It occupies the superior fossa of the 

 occipital bone, and rests on the tentorium. Its limits are to a consider- 

 able extent artificial. In front it is bounded by the external parieto- 

 occipital fissure, and by a line continuing the direction of the fissure 

 across the annectant convolutions to meet the inferior boundary of the 

 parietal lobe, and thence continued to the lower edge of this surface 

 at the anterior edge of the tentorium. 



Its convolutions, complex and ill-defined, are commonly described as 

 three in number, su^perior, middle, and inferior. They are continuous 

 Avith the, con volutions of the parietal and temporo-sphenoidal lobes by the 

 four annectant or connecting convolutions, of which ihQ first, passing round 

 the extremity, or in rare cases deeply across the bottom, of the external 



VOL. II, jl II 



