THE MAMMALIAN NERVOUS SYSTEM 105 



lowest mammals. See Herrick ('15), Fig. 106, h. sc, and 

 Johnston ('06), Chap. XVIII. These structures are smaller in 

 man than in the sheep, though they may still be recognized. 

 See Cunningham ('15), Fig. 554, p. 626; Morris ('14), Fig. 672, 

 p. 852; Spalteholz ('09), Fig. 715; Toldt ('04), Fig. 1198, p. 780; 

 Villiger ('12), Figs. 32-34, 36, 39. 



(3) Tractus olfado-corticalis lateralis. — These fibers arise 

 from the lateral olfactory nucleus and enter the ventro- 

 lateral end of the hippocampus in the uncus region of the 

 temporal lobe. They accompany those of the lateral olfactory 

 tract. 



The uncus and adjacent parts of the temporal lobe are of 

 transitional type. Forward they merge into the lateral ol- 

 factory nucleus, laterally into the neopallium (see Section 112) 

 through the gyrus hippocampi, and medially into the archipal- 

 lium through the hippocampus (see Section 127). 



127. The hippocampus and fornix. — When the relations of 

 the olfactory tracts of the sheep already described are clearly 

 in mind, remove the septum pellucidum and look into the 

 lateral ventricle, drawing apart the corpus callosum and the 

 underlying corpus fornicis (see Fig. 10). Locate the hippo- 

 campus in the floor of the posterior horn of the lateral ventricle; 

 also the fimbria and hippocampal commissure (the latter lying 

 in the corpus fornicis and connecting the hippocampi of the 

 two hemispheres) . Now cut through the splenium of the corpus 

 callosum, separating the parts last mentioned from the overly- 

 ing corpus callosum. Working carefully, continue this cut 

 laterally and ventrally, cutting from the ventricular wall 

 back into the lobus hippocampi and general cortex along the 

 posterior and outer border of the hippocampus for its entire 

 length downward to the tip of the gyrus hippocampi. Now 

 beginning in the gyrus hippocampi (into which the lateral 

 olfactory tract has already been traced), note carefully the 

 shape and position of the hippocampus and its fiber tract, the 

 fimbria, as you pass toward the midline. 



The hippocampus is the chief part of the archipallium, or 

 olfactory cerebral cortex. It is a buried convolution rolled 

 into the lateral ventricle from the ventral and occipital margins 

 of the cortex cerebri along the fissura hippocampi. It is en- 



