THE OLFACTORY APPARATUS 



217 



lution than the non-olfactory pallium and has, therefore, been 

 called the archipallium. The non-olfactory cerebral cortex is 

 termed the neopallium (or somatic pallium, for it receives the 

 somatic projection fibers). The archipallium, as already indi- 

 cated, attains its maximum development in the lowest mammals, 

 particularly the marsupials, like the kangaroo and opossum, 

 consisting of the hippocampus and hippocampal gyrus (gyrus 

 hippocampi, or pyriform lobe). The neopallium attains its 

 maximum size in the human brain, and the indications are that 

 in civilized races it is now in process of further differentiation. 

 In the human brain practically all parts of the exposed cerebral 

 cortex are neopallium, the archipallium being of relatively small 



Olfactory tract 



Granule cell 

 Mitral cell 

 Glomerulus 

 Olfactory nerve 

 Ethmoid bone 

 ~^ Olfactory epithelium 



Fig. 104. Diagram of the connections of the olfactory bulb. 



size and mostly concealed by a process of infolding along the 

 posterior margin of the neopallium. 



In the human body the specific olfactory receptors (see p. 92) 

 are limited to a small area of the mucous lining in the upper part 

 of the nasal cavity on both its lateral (Fig. 103) and its medial 

 walls. The cell bodies of the olfactory neurons of the first 

 order lie in this mucous membrane (Figs. 36 and 104). The 

 axons of these neurons form the fibers of the olfactory nerve, 

 which are unmyelinated; they pierce the ethmoid bone in nu- 

 merous small fascicles (fila olfactoria) and terminate by free 

 arborizations in the primary olfactory center within the olfac- 

 tory bulb (Figs. 53, 78, 103, 104). Several olfactory nerve- 

 fibers terminate together in a dense entanglement of fibers 



