THE OLFACTORY APPARATUS 221 



of Vicq d'Azyr, Figs. 78, 106), for the correlation of olfactory with 

 general somatic reactions. There is also a direct path between 

 the secondary olfactory area and the cerebral peduncle, without 

 connection with the diencephalon, by way of the tractus oLfacto- 

 tegmentalis (Fig. 106). In the epithalamus the olfactory ner- 

 vous impulses are correlated with those of the somatic sensory 

 centers of the thalamus, especially the optic and tactual sys- 

 tems (p. 162) ; in the hypothalamus they are correlated with gus- 

 tatory and various visceral sensory systems (p. 163). 



The preceding account includes a description of a few of the 

 more important pathways involved in olfactory reflexes. Ol- 

 factory impulses which reach the cerebral cortex take a different 

 path. They are carried from all parts of the secondary olfactory 

 area at the base of the olfactory bulb into the hippocampus 

 (which composes the greater part of the archipallium in the 

 human brain) by several olfacto-cortical tracts, whose courses 

 in the human brain are so tortuous that we shall not attempt to 

 describe them here. 



The hippocampus (formerly called the Ammon's horn or cornu 

 Ammonis, also the hippocampus major, Fig. 107) is a special 

 convolution which forms the postero-ventral border of the cere- 

 bral cortex; it is rolled into the posterior horn of the lateral 

 ventricle so that it does not appear on the surface of the brain. 

 It is connected with the remainder of the cortex (neopallium) 

 by cortex of transitional type, the hippocampal gyrus (gyrus 

 hippocampi), from which it is separated by a deep groove, the 

 fissura hippocampi. The free border of the hippocampus is 

 accompanied for its entire length by a strong band of fibers, the 

 fimbria, through which olfactory projection fibers enter it from 

 the secondary olfactory area. These fibers discharge into a 

 subsidiary part of the hippocampus, the dentate gyrus (gyrus 

 dentatus, also called fascia dentata), at a, Fig. 107. 



The hippocampus is connected with all other parts of the cere- 

 bral cortex by an extensive system of association tracts forming 

 the alveus (Fig. 107), thus providing for those complex inter- 

 actions of diverse functional systems for which the cortex is 

 especially adapted. There is also an efferent pathway from the 

 hippocampus to the brain stem through the fimbria and the 

 column of the fornix (Figs. 78, 107), whose fibers terminate in 



