17S 



AXATOMY OF THE CENTKAL XEBTOUS SYSTEM. 



divides into two parts: one bundle going to the Ggl. habeniilje, — Tr. 

 Coiiico-habenularis, — and another one to the Corpus mamillare on the base 

 of the hypothalamns, — Tr. cortico-mamiUaris (see Fig. 100). The latter, 

 especially, is a well defined bundle easily followed in its course, long known 

 in mammals as the Fornix column. In birds it is very thin. In birds and 

 reptiles the fornix passes in a rather straight course from its origin to its 

 terminus. But in mammals, where, through the great development of the 

 mantle, the olfactory cortex recedes far to the posterior and in part bends 

 ventrally (Figs, lo'i, 133, and 143), the Tr. cortico-inamiUaris must follow 



Meclio-dors cortex. Ammon's horn A' ^ 



Epistrintiim ^^ 

 Post, end of septum fimbria ^_. 

 Fiss. arcuat. aepti _. 

 Plexus chovioid. 

 Taiuia 



Tr. thalamo-raamill. _, 



Tr. olf. lialjenul. 



Fornix 



Tr. strio-thalamicus - — 



Tr. septo-mesencepbalicus __ 



Fig. 120. — Frontal section through the posterior cerebral portion of the 

 giant snake: Pijflwii, bii'ittatiis. Dorsal, the mantle; ventral, the transitional 

 region of the Thalamus. 



the margin of the hemisphere and run a rather long arcuate course before 

 it can turn down to the corpus mamillare just behind the commissura 

 anterior. 



Besides the Fornix system the olfactory cortex is characterized by a 

 commissural system which connects the right side with the left. Its 

 bundles are designated as C ominissiira ant. and post, pallii. In mammals 

 the whole complex is called the Psalterium. In the lowest orders of mam- 

 mals it forms the only mantle commissure; in the higher orders there is a 

 second commissure, the Corpus callosum. The latter connects mantle-areas 

 which do not belong to the olfactory apparatus, and is usually, especially in 

 man, much larger than the commissures of the olfactory mantle, because. 



