THE ESSENTIALS OF HISTOLOGY. 



ing neuroglia (1, 2, 3), as in the olfactory tract, but below this ring- 

 several layers are recognised as follows : 



1. A white or medullary layer (fig. 284, 4, 5), characterised by the 

 presence of a large number of small cells ("granules ") with reticulating 

 bundles of medullated nerve-fibres running longitudinally between 

 them. 



2. A layer of large nerve-cells (6), with smaller ones intermingled, the 

 whole embedded in an interlacement of fibrils which are mostly derived 

 from the cell-dendrites. From the shape of most of the large cells of 

 this layer (fig. 285, m.c.) it has been termed the " mitral " layer. These 



olf.c. 



FIG. 285, DIAGRAM TO SHOW THE RELATIONS OF CELLS AND FIBRES IN THE 

 OLFACTORY BULB. 



olf.c., olfactory cells of M. Schultze in the olfactory mucous membrane, sending their 

 basal processes as iion-medullated nerve-fibres into the deepest layer of the olfactory 

 bulb(o//.n.) ; gl, olfactory glomeruli containing the terminal arborisations of the olfactory 

 fibres and of processes from the mitral cells ; m, mitral cells, sending processes down to 

 the olfactory glomeruli, others laterally to end in free ramification in the nerve-cell layer, 

 and their axis-cylinder processes, a, a, upwards, to turn sharply backwards and become 

 fibres of the olfactory tract (tr.olf.). Numerous collaterals are seen curving off from these 

 fibres : '. a nerve-fibre of the olfactory tract apparently ending in a free ramification in 

 the olfactory bulb. 



cells send their axis-cylinder processes upwards into the next layer, 

 and they eventually become fibres jof the olfactory tract and pass along 

 this to the base of the brain, giving off numerous collaterals into the 

 bulb as they pass backwards (v. Gehuchten). 



3. The layer of olfactory glomeruli (fig. 284, 7 ; fig. 285, gl.) consists of 

 rounded nest-like interlacements of fibrils which are derived on the 



