320 



NERVOUS SYSTEM OF VERTEBRATES. 



Where the commissure crosses in the lamina terminahs the latter 

 is thickened by gray matter which has invaded it from the adjacent 

 mesial olfactory nucleus or paraterminal body (Fig. 163). In the 

 upper part of the lamina terminahs the hippocampal commissure 

 crosses in front of the foramen of Monro and covers the face of the 

 hippocampus which bounds the lateral ventricle. Upon the 

 upper surface of the hippocampal commissure in the middle Une 

 appears the small recessus superior. The hippocampal commis- 

 sure is derived wholly from the hippocampal fold of the mesial 

 wall of the hemisphere, while the dorsal and lateral wall or gen- 

 eral cortex contributes fibers to the anterior commissure. 



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Fig. 161. — Portion of a transverse section through the brain of a Monitor 

 {Hydrosaurus). From G. Elliot Smith. In the figure to the left the line x-y, 

 shows the plane of the section, alv., alveus; c./., columna fornicis; fasc, fascic 

 ulus marginaHs; hip., hippocampus; para., paraterminal body; rec.s., recessus 

 superior; c.d., hippocampal commissure; c.v., anterior commissure. 



In sagittal section near the medial plane (Fig. 164) are to be 

 seen the following tracts belonging to the olfactory apparatus. 

 The tractus olfactorius (olfactory peduncle) enters the tuberculum 

 olfactorium and the precommissural body and also sends a part 

 of its fibers up into that part of the hippocampal formation known 

 as the fascia dentata. The latter fibers are a vestige of the 

 olfactory tract fibers which run to the epistriatum in fishes. From 

 the tuberculum olfactorium a large tract, not shown in the figure, 

 goes up through the precommissural body to the hippocampus. 



