832 



THE NERVOUS SYSTEM 



inferior surface, are the tela chorioidea of the third ventricle, the fornix, the septum 

 pellucidum, and the medial walls of the lateral ventricles. 



Each cerebral hemisphere includes (1) a superficial and much folded mantle 

 or pallium, divided into lobes and gyri, and consisting of grey substance, the cortex, 

 covering an abundant mass of white substance; (2) a modified portion, the rhmen- 

 cephalon, having especially to do with the impulses brought in by the olfactory nerve; 

 (3) a cavity, the lateral ventricle; and (4) a buried mass of grey substance or basal 

 ganglia which together with the internal capsule of white substance, is known as the 

 corpus striatmn. 



Gyri, fissures, and sulci. The cerebral pallium is thrown into numerous and 

 variable 'folds or gyri (convolutions). These are separated from each other by corre- 

 sponding furrows, the deeper and most constant of which are called fissures; the re- 

 mainder, sulci. All the fissures and the main sulci are named. There are, however, 

 numerous small and shallow sulci to which names are seldom given. These occur 

 as short branches of main sulci or as short, isolated furrows bounding small gyri 

 which connect adjacent gyri. These small gyri are likewise seldom given individual 



FIG. 620. DIAGRAM OF CONVEX SURFACE OF RIGHT CEREBRAL HEMISPHERE AND PAUT or 

 UPPER SURFACE OF CORPUS CALLO.SIM. 



PARAMESIAL SULCUS 



SUPERIOR FRONTAL SULCUS 



OUTLINE OF LAT- 

 ERAL VENTRICLE. 

 LA TERAL LONGI- 

 TUDINAL STRIA 



.MEDIAL LONGI- 

 TUDINAL STRIA 



CORPUS CALLOSUM 



MESIAL SULCUS 

 INFERIOR FRONTAL 



SULCUS 

 PRECEXTRAL SULCUS 



CENTRAL SULCUS 

 (SOLA SI U) 



POSTCENTRAL 



SULCUS 



LA TERA L FISSURE 

 (SYLVII) 



INTRAPARIETAL 

 8ULCU& 



LA TERAL OCCIPITAL 

 SULCUS 



TRANSVERSE OCCIPITAL 

 SULCUS 



names. They are very variable both in different specimens and in the two hemi- 

 spheres of the same specimen. Collectively, they are the so-called gyri transitivi 

 Certain groups of them are named according to their locality, such as orbital gyri and 

 lateral occipital gyri. Even the main gyri (and sulci) are very irregular in detail. 

 Some of the main and deeper fissures are considerably deeper than others. Some are 

 infoldings of the grey cortex, so deep that a portion of their course may be indicated 

 as slight bulgings in the walls of the lateral ventricles, e.g., the hippocampal and 

 collateral fissures. While the general surface pattern is similar for all normal human 

 brains, yet when a detailed comparison is made, the given gyri of different specimens 

 are found to vary greatly. Neither are the main gyri of the two hemispheres of the 

 same brain ever entirely alike. 



Origin of the Gyri. The gyri (and sulci) are the result of processes of unequal growth 

 folds necessarily resulting from the surface portion of the hemispheres increasing much more 

 rapidly than the central core. In the early periods of fetal life the surfaces of the hemispheres 

 are quite smooth. In many of the smaller mammals this condition is retained throughout life, 

 but in the larger mammals, including man, as development proceeds the cerebral cortex becomes 

 thrown into folds. The absolute amount of the grey substance of the hemispheres varies with 



