THE CEREBRAL HEMISPHERES 



<)45 



in each half fornix, but a number course transversely to enter the cms fornicis 

 of the opposite side to end in the hippocampal formation. These fibres, of 

 transverse course, form a thin lamina filling in the small triangular space in the 

 subsplenial region between the converging crura fornicis and constituting the 

 hippocampal commissure (lyra; psalterium). Occasionally a small recess called 

 Verga's ventricle is formed between the corpus callosum and the hippocampal 

 commissure. 



The two half fornices now become joined in the mesal plane and, leaving the 

 subsplenial surface of the corpus callosum, dip frontoventrad in an arch the 

 body of the fornix. Its caudal part is broad and each half is of triangular outline 

 (on section) with a sharp edge directed laterad. Where it is not in contact with 

 the corpus callosum it affords attachment, on each side of the mesal plane, to 

 the hemiseptum of the septum lucidum. Laterad of these lines of attachment 

 the dorsal surface of each fornix enters into the formation of the floor of the lateral 



PSEUDOCELC 



FK:. t)99. A frontal section of the brain slightly caudad of the genu of the corpus callosum. 



ventricle and is covered by ependyma (Fig. 690). The ventral surface rests 

 upon the velum interpositum, which separates it from the third ventricle and the 

 dorsal surface of the thalamus (Fig. 666). 



Near the region of the anterior commissure the fornix again divides into its 

 constituent lateral halves, separating as rounded strands called the anterior 

 pillars (fornicolumns). These curve ventrad to form the frontal boundary of the 

 foramen of Monro and thence plunge into the hypothalamic gray, inclined slightly 

 caudad, to end in the corpus albicans. The terminals of the fornix fibres come 

 into relation with the cells of the nucleus of the corpus albicans, which, in turn, 

 give off the bifurcating Y-shaped axone bundles already described (p. 908). 



In rare instances each anterior pillar has been seen to divide on approaching 

 the anterior commissure, a part passing frontad thereof as an anomalous pre- 

 commissural pillar of the fornix. The fornix, in its course from hippocampus 

 to corpus albicans, gives off, in addition to those described as hippocampal 

 commissural fibres, axones (a) to the opposite half fornix, decussating in the 

 fused portion (body), (6) to the hemiseptum of the septum lucidum, and (c) to 



