y ///; 



S3 1 



The corpus callosum. -In their early development as lateral dilations of the 

 anterior primary l>r:iin-vesirles. the hemispheres are connected with each Other 

 only at the anterior end of the t halamenceplialon. where they are liolh continuous 

 with the lamina termiiuilis. As development proceeds and the hemispheres extend 

 upwards, backwards, forwards, and laterally to completely conceal I he base, and as the 

 pallium thicken:- and its folds begin to appear, (lie two hemispheres become united 

 across l he mic 1-line abo ve t he t halamenceplialon and the third ventricle by the formation 

 of the great cerebral commissure, the corpus callosum. After removal of the falx 

 rerebri from the longitudinal fissure, the dorsal surface of the corpus callosum may be 

 exposed by drawing apart the cont iguous mesial surfaces of the hemispheres. It con- 

 sists of a dense mass of pure \\hite substance coursing transversely, and arises as out- 

 growths from the cortical cells of both hemispheres. Thus it is the great pathway which 



viates the cortex of the two sides of the telencephalon. Only the smaller medial 

 portion of the body lies free in the floor of the longitudinal fissure, by far the greater 

 part being concealed in the. substance of the hemispheres, where its fibres radiate to and 

 from different localities of the pallium, forming the radiulwn of the corpus callosum. 

 Its surface shows numerous transverse markings, the transverse stria', which indicatethe 



FIG. 019. MESIAL AND TENTOUIAL SURFACES OP RIGHT CEREBRAL HEMISPHERE, VIEWED FROM 

 DIE LEFT. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) 



,vr/.(7.s HI' THE cintlTS CAL/.oxr.M 

 BOD Y OF FORM* ; 

 BODY Of COXPUS CALLOBPM ' ' TllAI.AMi* 



INTKin-KSTKUTHK FOKAUKX \^, j ' ' CR US OF FOKX/.Y 



__, , ,_ ..._ CUT SURFACE OF CEREBRAL 



OEXU OF co/i ITS ^JT "f \ | .' Jf ,' F" ^1^. PEDUNCLE 



CALLOSUM m m ^ _ ._, __ ,__ 



SPLEXIUM OF CORPUS 



PILLARS or /-'on \i.v 



A NTERIOR COM Miss I '/; /: 



OPTJC c/lfASMA 

 //I. /. i/.'.v OF roi:\i.\ _ 

 CORPUS MA '/)///,/. i /,/: \ llirrocAMl-Ai. 



Impression for petrous bone 

 TIIALAMO-MA.MMILLARY FASCICULUS DEXTA TK FASCIA 



OF KYRUS FORXICA- 



. \ n > 



\ cm II! 101 1) FISSURE 

 flMBRIA 



course of its component bundles of fibres. In addition there may be seen two delicate, 

 variable longitudinal bands running over its surface on each side of the mid-line. The 

 medial longitudinal stria runs close to the median plane, around the anterior end 

 into the gyrus subcallosus (fig. 620) , and over the posterior end downwards and lateral- 

 \\ards to connect wit h the hippocampal gyrus of the base of the telencephalon. The 

 lateral longitudinal stria is more delicate than the mesjal stria, and courses lateral- 

 wards, and can only be seen within the sulcus of the corpus callosum (fig. 620). 



When severed along the median plane, it may be seen that the anterior margin of 

 the corpus callosum is turned abruptly downwards, forming the genu, and that this 

 turn continues, so that the tapering edge of the body points posteriorly and constitutes 

 the rostrum (iigs. til.") and (HO). The rostrum is in contact with the lamina terrninalis 

 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 backwards as the body of the corpus callosum, and ends over the 

 corpora iaiadrigemina in its rounded, thickened posterior margin, the splenium. It 

 is bounded above by the sulcus of the corpus callosum, and, attached to its concave 



