THE BRAIN OF MAMMALS AND THE OLFACTOET APPARATUS. 217 



The corima Ammonis themselves possess a distinct eomnmnication with 

 one another: an extensive system of fibers extends between them. It is 

 called the commissure of the •eornu Ammonis, or the psalterium. 



The cornu Ammonis is connected with the olfactory lobe by the mesial 

 olfactory radiation already mentioned. As the tractus eortico-olfactorins 

 septi, it was first seen to appear in the reptiles; the greatest part of its 

 course is visible in Fig. 144. In the higher mammals and in man the tract 

 is not to be recognized without further study, and by no means as readily 

 as in the brain of the marsupial, shown in Fig. 123. Nevertheless, Zucker- 

 kandl has succeeded in demonstrating its existence in an entirely satisfactory 

 manner, and this wholly independently of the more recent, comparative ana- 

 tomical considerations. He has named it the olfactory bundle of the cornu 

 Ammonis. 



Fig. 143. — Median sagittal section through the brain of a calf. The lobus 

 limbieus is shown somewhat lighter. 



The greater portion, at all events, springs from the medulla of the olfactory 

 field. The large tract of fibers arises on the under side of the brain in the cortex of 

 the olfactory area^ then turns over this toward the median line (see Figs. 141 and 

 144) and passes along beneath the gyrus subeallosus (Figs. 133 and 135) dorsally, 

 up to the septum pellucidum. In the septum a part of the fibers cross and another 

 part goes directly backward. Both bundles, reunited, meet with the fornix at the 

 posterior margin of the septum and run farther backward in it as far as the medulla 

 of the cornu Ammonis. 



For that which follows, compare especially Fig. 144. 



The olfactory lobe and the olfactory field have, in the main, received 

 the afferent tracts, the olfactory-nerve pathways of the second order, from 



