852 



THE NERVOUS SYSTEM 



constitutes the rostrum (figs. 667, 671). The rostrum is in contact with the 

 lamina terminahs of the third ventricle below by a short, thin, dorso-frontal 

 continuation of this lamina, known as the rostral lamina. The rostral lamina may- 

 be considered as beginning at the anterior cerebral commissure with the anterior 

 aspect of which it is in contact, and extending to the rostrum. Beginning with the 

 rostrum and genu, the corpus callosum arches backward as the body of the corpus 

 callosum, and ends over the quadrigeminate region in its rounded, thickened 

 posterior margin, the splenium. It is bounded above by the sulcus of the corpus 

 callosum, and, attached to its concave inferior surface, are the chorioid tela 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 palliuni, divided into lobes and gyri, and consisting of grey substance, the 

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



Fig. 672. — Diagram of Convex Surface of Right Cerebral Hemisphere and Part op 

 Upper Surface of Corpus Callosum. 

 Paramesial sulcus 



/ Superior frontal sulcus 



Outline of lateral 

 ventricle 



Lateral longitudinal stria 



Medial longitudinal stria 



Corpus callosum 



Middle frontal sulcus 

 Inferior frontal sulcus 

 Precentral sulcus 



Central sulcus (Rolandi) 



Postcentral sulcus 

 11 Lateral fissure (Sylvii) 



Intraparietal sulcus 

 Lateraroccipital sulcus 

 Transverse occipital sulcus 



rhinencephalon, having especially to do with the impulses brought in by the olfac- 

 tory nerve; (3) a cavity , the lateral ventricle; and (4) a buried mass of grey sub- 

 stance, the caudate and lenticular nuclei, which together with the internal capsule 

 of white substance, are known as the corpus striatum. 



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

 varial)le folds or gyri (convolutions). These are separated from each other by 

 corresponding furrows, the deeper and most constant of which are called fissures; 

 the remainder, 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 names. They are very variable both in different specimens and 

 in the two hemispheres of the same specimen. Collectively, they are the so-called 

 transitory gyri (gyri transitivi). Certain groiips of them are named according to 

 their locality, such as orbital qyri and lateral occipital gyri. Even the main gyri 

 [gyri profundi] (and sulci) are very irregular in detail. Some of the main and 

 deeper fissures are considerably deeper than otiiers. Some are infoldings of the 

 grey cortex so deep that a i)ortion of their course may be indicated as slight bulgings 

 in the walls of the lat(Tal ventricles, e. g., the hi])pocampal and collateral fissures. 

 While the general surface pattern is simihir for all normal human brains, yet when 

 a detailed comparison is made, the given gyri of different specimens are found to 



