842 



THE NERVOUS SYSTEM 



The angular gyrus is the portion which embraces the posterior end of the superior 

 temporal sulcus, and is continuous behind this into the middle temporal gyrus and 

 in front with the superior temporal gyrus. Its shape is usually such as to suggest 

 its name. The most posterior part of the inferior parietal lobule, when arching in a 

 similar way about the end of the middle temporal sulcus and continuous with the 

 temporal gyri on its either side, is known as the post-parietal gyrus. This is a 

 smaller area than either of the other two, and, owing to the variability of the end of 

 the middle temporal sulcus, is not always evident. 



The mesial surface of the parietal lobe is divided into two parts by the marginal 

 portion of the sulcus cinguli. The anterior and smaller part is the mesial continuation 

 of the posterior central gyrus, and comprises the posterior portion of the paracentral 

 lobule. It is limited from the part of this lobule belonging to the frontal lobe by a 

 vertical line drawn from the marginal extremity of the central sulcus. The praecu- 

 neus (quadrate lobule) is the posterior and larger part of the mesial surface of the 

 parietal lobe. It is separated from the cuneus of the occipital lobe by the parieto- 

 occipital fissure, and is imperfectly separated from the gyrus cinguli (limbic lobe) 



FIG. 626. OUTLINE DRAWING OF MESIAL SURFACE OF LEFT CEREBRAL HEMISPHERE. 

 (After Toldt, " Atlas of Human Anatomy," Hebman, London and New York.) 



SULCUS CINGULI 

 (marginal poi-tiiiu) 



SUBPARIETAL SULCUS 

 PARIBTO-OCCIPI- 

 TAL FISSURE 



CALCARINE 



FISSURE 



CENTRAL SULCUS (ROLAXDI) 



I -l/.I.SS.l I\TKI!MEDIA 



1 ' SULCUS CI\I,I'I f 



(a uhfron Inl portion) 



SULCUS CORPORIS 

 CALLOSI 



SUPERIOR 



\ 



<:EXI- OF CORPUS 

 C&LLOSUM 



XESEXCEPHA LOlf 



HYPOPHYSIS 



TUBER CIXEREUX 



\ ROSTRUM OF CORPUS CAI.LOSU.V 

 \ \ \ > 



\ i \ A.\TERIOR PAROLFACTORY SU1.1TS 

 \ \ I'Mtnl.t 'X -TIIKT AREA (BROCA'S AHE.t) 

 \ * POSTERIOR PAROLFACTORY SULCCS 

 'SL'B-CALLOSAL OTRVS (PEJ>UXCLE OF 

 \ CORPUS CALLOSUJf) 



INFUNDIBULUil 



below by the subparietal sulcus (postlimbic fissure), branches of which invade it ex- 

 tensively. 



The occipital lobe. This is a relatively small, trifacial, pyramidal segment, 

 comprising the posterior extremity of the hemisphere, its apex being the occipital 

 pole. Though one of the natural divisions of the cerebral hemisphere, it is very in- 

 definitely marked off from the lobes anterior to it. Though it contains the cortical 

 area of the visual apparatus, only in the brains of man and the apes does it occur as a 

 well-defined projection. In most of the mammalia it is not differentiated at all. 

 Its three surfaces comprise a convex, a mesial, and a tentorial surface. 



Its convex surface is separated from that of the parietal and temporal lobes by the 

 superior and external extremity of the parieto-occipital fissure, and by an arbitrary 

 line drawn transversely from this extremity to the infero-lateral borderof the hemi- 

 sphere, or so drawn as to bisect the pre-occipital notch when this is evident. The 

 sulci which occur on the convex surface may be described as two, though both of 

 these are very variable in their extent and shape, and their branches are inconstant 

 both as to number and length. (1) The transverse occipital sulcus is the most 



