NERVE 



135 



human brain. To this the fibres from the olfactory bulb, the 

 secondary olfactory neurons, pass. These form synapses from 

 which the tertiary olfactory neurons pass to the fascia dentata 

 running along the edge of the hippocampus, and to tlie hippo- 

 camiJus {He). From these structures the fornix {F.) arises 

 which carries fibres across to the opposite hippocampus 

 and backwards on the same side to the thalamus {T.A.). The 

 olfactory fibres from the pyriform lobe have also extensive 

 sub-thalamic connections. They pass to form synapses in 

 each corpus mammillare {M.), from which fibres extend down 

 in the tegmentum, probably to act on the spinal arcs. 



Fig. 61. — Side view of the Cerebrum of one of the Lowest Mammals. B.O., 

 olfactory bull) ; y.O.Zr., olfactory tract; Twierc, olfactory tubercle; 

 L.P., lobus pyriformis ; f.r., fissura rhinica, above which is the neo- 

 pallium, divided into receiving areas ; //'", visual ; VIH'", auditory ; 

 yS'", sensations from body; V", sensations from face ; L.A.H., motor 

 areas for leg, arm, and head. (Elliot Smith.) 



The evidence points to the hippocampus, including the 

 fascia dentata, being the receiving area, the area which 

 when stimulated, gives rise to sensations of smell, while the 

 fibres of the fornix serve to connect these impressions with 

 those from the other sense organs. 



The cortex in this olfactory region, the rhinencephalon, 

 contains cells arranged in two layers — (1) outside a layer of 

 small cells, often in clusters, the granular layer; (2) below 

 this layers of larger cells, the suh-granular layer. The fibres 

 passing to it get their medullary sheaths at an early stage 

 of development. 



