INTERIOR OF CEREBRUM. 



591 



in length, extending to within an inch and a half of the anterior, and to within 

 two inches and a half of the posterior, part of the brain. It is somewhat 

 broader behind than in front, and is thicker at either end than in its central 

 part, being thickest behind. It presents a somewhat arched form, from 

 before backwards, terminating anteriorly in a rounded border, which curves 

 downwards and backwards, between the anterior lobes to the base of the brain. 

 In its course, it forms a distinct bend, named the knee, or genu, and the reflected 

 portion, named the leak (rostrum), becoming gradually narrower, is attached to 

 the anterior cerebral lobe, and is connected through the lamina cinerea with 

 the optic commissure. The reflected portion of the corpus collosum gives off, 

 near its termination, two bundles of white substance, which, diverging from one 

 another, pass backwards, across the anterior perforated space, to the entrance 

 of the fissure of Sylvius. They are called the peduncles of the corpus callosum. 



Fig. 330. Section of the Brain. Made on a level with the Corpus Callosum. 



Posteriorly, the corpus callosum forms a thick, rounded fold, which is free for 

 a little distance, as it curves forwards, and is then continuous with the fornix. 

 On its upper surface, its fibrous structure is very apparent to the naked eye, 

 being collected into coarse, transverse bundles. Along the middle line is a 

 linear depression, the raphe, bounded laterally by two or more slightly elevated 

 longitudinal bands, called the striae kngitudinales, or nerves of Lancisi; and, still 

 more externally, other longitudinal striae are seen, beneath the convolutions 

 which rest on the corpus callosum. These are the strive lonrjitudinales laterales. 

 The under surface of the corpus callosum is continuous behind with the fornix, 

 being separated from it in front by the septum lucidum, which forms a vertical 

 partition between the two ventricles. On either side, the fibres of the corpus 



