THE CEHEBRUM OE PROSENCEPHALON. 



151 



at least in large reptiles, between the cortex of the olfactory lobes and the 

 epistriatum: Tr. cortico-epistriaticus. 



The olfactory apparatus, then, as far as described, consists of a com- 

 bination of at least two neurons: a peripheral neuron of the I order, from 

 the nasal mucous membrane to the bulbus; and a central neuron of the 

 II order, from the bulbus to one of the several termini above enumerated. 

 But from these terminations proceed other tracts of the third, or higher, 

 order. In the first place, the olfactory centers — i.e., the terminations of the 

 II neuron are uniformly connected by a tract with the Epithalamus, espe- 

 cially with the Ggl. habenulae. Carefully study these relations in Fig. 98. 



Epistriatum 



- Resio part. caud. sti-iat. 

 -Taaaia with three origina of bundles 



- lVucIcus tEKiiise 



Tr. strio-thalamieus 



Tr. septo-mesenceph. 

 Decuss. transverse 



Fig. 99. — Frontal section through the most posterior portion of the Cere- 

 brum of the Swamp-turtle: Emys lutaria. Note dorsaJly the mantle with its 

 cortex, ventrally the transition to the thalamus with the underlying chiasma, 

 at the right the posterior end of the olfactory region. 



A second connection passes from the olfactory center to the brain- 

 cortex. This tract might be designated the Tr. cor tico-olf actor ii. It is 

 absent in fishes, is probably present in amphibians and birds, and is well 

 developed in reptiles and mammals. 



The cortico-olfactory tract is, as you will find later, the first connection 

 which was established between the brain-cortex and any sensory apparatus. 

 Just because of this important fact this tract will be discussed later in 

 connectiou. with the development of the brain-mantle. 



