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HAND-BOOK OF PHYSIOLOGY. 



2. Parietal (P.). This lobe is bounded in front by the fissure of Bo- 

 lando, behind by the external perpendicular fissure (parieto-occipital), and 

 below by the fissure of Sylvius. Behind the fissure of Rolando is the "as- 

 cending" parietal" convolution, which swells out at its upper end into what 

 is termed the superior parietal lobule. The superior parietal lobule is 

 separated from the inferior parietal lobule by the mtra-parietal sulcus. 

 The inferior parietal lobule (pli courbe) is situated at the posterior and 

 upper end of the fissure of Sylvius; it consists of (a) an anterior part (supra- 

 marginal convolution) which hooks round the end of the fissure of Sylvius, 

 and joins the superior temporal convolution, and a posterior part (b) (angu- 

 lar gyrus) which hooks round into the middle temporal convolution. 



FIG. 383. View of the brain from above (semi-diagrammatic). SI, end of horizontal ramus of fis- 

 sure of Sylvius. The other letters refer to the same parts as in Fig. 332. (Ecker.) 



3. Temporo-splienoidal (T. ), contains three well-marked convolutions, 

 parallel to each other, termed the superior, middle, and inferior temporal. 

 The superior and middle are separated by the parallel fissure. 



4. Occipital (0.). This lobe lies behind the external perpendicular or 

 parieto-occipital fissure, and contains three convolutions, termed the supe- 

 rior, middle, and inferior occipital. They are often not well marked. In 

 man, the external parieto-occipital fissure is only to be distinguished as a 

 notch in the inner edge of the hemisphere; below this it is quite obliter- 

 ated by the four annectent gyri (plis de passage) which run nearly hori- 

 zontally. The upper two connect the parietal, and the lower two the tem- 

 poral with the occipital lobe. 



5. The central lobe, or island of Eeil, which contains a number of 

 radiating convolutions (gyri operti). 



The internal surface ^Fig. 334) contains the following gyri and sulci: 

 Gyrus fornicatus, a long curved convolution, parallel to and curving 

 round the corpus callosum, and swelling out at its hinder and upper end 



