MINUTE STRUCTURE OF THE OLFACTORY LOBE. 



175 



of which pass upwards through the granule layer, while most of their protoplasmic 

 or dendritic processes enter the next stratum. 



(2.) The layer of olfactory glomeruli (7). The remarkable bodies which 



Fig. 126. SECTION ACROSS A PART 



OF THE OLFACTORY Bt'LB 



(Heiile). 



1, 3, layers of very fine trans- 

 versely cut nerve-fibres, passing 

 round into one another at the 

 side, and forming the flattened 

 medullary ring, enclosing the cen- 

 tral neuroglia, 2 ; 4, 5, 6, granule- 

 layer ; 7, layer of olfactory glome- 

 ruli, f, ft ; 8, layer of olfactory 

 nerve-fibres, bundles of which are 

 seen passing at * * to the olfactory 

 mucous membrane. 



characterize this stratum 

 were first described by Ley- 

 dig in elasrnobranchs and 

 by Lockhart Clarke in 

 mammals. They are rounded 

 bodies which are formed of 

 a dense interlacement of 

 nerve-fibres derived on the 

 one hand from the dendrites 

 of the mitral cells, on the 

 other from the olfactory 

 fibres of the next layer. They also include a few small cells,\vhich are probably neuroglial. 

 (3.) The layer of olfactory nerve-fibres (8). This, the deepest layer of the bulb, 



Fig. 127. * DIAGRAM OF THE 



CONNECTIONS OK CELLS AND 

 FIBRES IN THE OLFACTORY 

 BULB. (E. A. S.) 



olf.c., cells of the olfactory 

 mucous membrane ; olf.n., 

 deepest layer of the bulb com- 

 posed of the olfactory nerve- 

 fibres, which are prolonged 

 from the olfactory cells; gl., 

 olfactory glomeruli, containing 

 arborisations of the olfactory 

 nerve-fibres and of the den- 

 drites of the mitral cells ; m.c. , 

 mitral cells ; a, their axis- 

 cylinder processes passing to- 

 wards the nerve-fibre layer, 

 n.tr., of the bulb to become 

 continuous with fibres of the 

 olfactory tract : these axis- 

 cylinder processes 'are seen to 

 give off collaterals, some of 

 which pass again into the 

 deeper layers of the bulb ; 

 n', a nerve- fibre from the 

 olfactory tract ramifying in 

 the grey matter of the bulb. 



olj. 



consists entirely of bundles of non-medullated nerve-fibres, which here form a dense 

 plexus the fibres of which on the one hand pass through the perforations in the 



