THE CEBEDEUM. 



693 



Fig. 330 



whicli IS the foramen of Monro, or orifice communicating with the two ven- 

 tricles. On the floor of these cavities is observed two large eminences the 

 corpus stnatum and the hippocampus ; with a vascular and apparently granu- 

 lated cord forming the cerebral choroid plexus, a dependency of the velum inter- 

 positum. 



It now remains to enter into some detail with regard to the anatomical 

 characteristics of all these parts. 



1. The Corpus Gallosum. (Figs. 327, 330.) 

 _ The corpus callosum is a kind of arch thrown over the two lateral ven- 

 tricles, while at the same time it is a commissure uniting the two hemispheres. 

 It belongs exclusively to mammalia. 



_ Composed entirely of white substance, it affects a quadrilateral form, 

 being elongated in an antero-posterior direction, and thus presents for study 

 two faces, two herders, and two extremities. 



The superior face, free in the middle, and corresponding to the bottom 

 of the interlobular fissure, is covered right and left by the substance of the 

 hemispheres. It is traversed from before to behind by two white, and u 

 generally very delicate, cords, the tractus ' longitudinalis (the chordae " 

 longitudinalis of Lancisii) of the corpus callosum, which lie together on th«/ 

 middle line. The inferior face is 

 divided by the insertion of the sep- 

 tum lucidum into two lateral por- 

 tions, each of which forms the roof 

 of one of the cerebral ventricles. 



The two lateral borders of the 

 corpus callosum disappear in the 

 central substance of the hemis- 

 pheres, where it is almost impos- 

 sible to distinguish their limits. 



The posterior extremity appears 

 at the bottom of the interlobular 

 fissure, after the destruction of the 

 adhesion usually established above 

 it between the two hemispheres, in 

 the form of a thick, rounded en- 

 largement (splenium) folded in 

 genu, below, and confounded with 

 the middle part of the fornix. It 

 is prolonged, laterally, above the 

 ventricular cavities, by forming two 

 angles (linece transversa) which are 

 soon lost in the white central sub- 

 stance of the cerebrum. 



The anterior extremity comports 

 itself in a similar manner between 

 the anterior lobes of the hemi- 

 spheres. 



2. ITie Lateral or Cerebral Ventricles. (Figs. 325, 331.) 



The lateral ventricles are two large elongated cavities excavated in the 

 hemispheres, lying against each other in their anterior moiety, and divergent 

 in their posterior part, which is very much curved backwards, outwards, and 

 downwards, to open into the substance of the mastoid lobule. 



47 



THE CORPUS CALLOSUM, AFTER REMOVAL OP 

 THE UPPER PORTION OP THE CEREBRAL 

 HEMISPHERES. 



1, Centrum orale of Vieussens; 2, 2, Chords 

 longitudinales ; 4, 4, Cornua, or angles of the 

 posterior extremity; 5, 5, Ditto of aucerior 

 extremity. 



