532 



THE NERVOUS SYSTEM. 



" 1. A white or medullary layer, characterized by the presence 

 of a large number of small cells (< granules') with reticulating 

 bundles of medullated nerve-fibers running longitudinally between 

 them. 



" 2. A layer of large nerve-celh, with smaller ones intermingled, 

 the whole embedded in an interlacement of fibrils which are 

 mostly derived from the cell-dendrons. From the shape of most 

 of the large cells of this layer it has been termed the ' mitral ' 

 layer. These cells send their neurons upward into the next layer, 



FIG. 310. Diagram of the connections of cells and fibers in the olfactory bulb: 

 olf.c, cells of the olfactory mucous membrane; oZ/.n, deepest layer of the bulb, 

 composed of the olfactory nerve-fibers which are prolonged from the olfactory 

 cells ; gl, olfactory glomeruli, containing arborization of the olfactory nerve-fibers 

 and of the dendrons of the mitral cells ; m.c, mitral cells ; a, thin axis-cylinder 

 process passing toward the nerve-fiber layer, n.tr, of the bulb to become continuous 

 with fibers 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 ; ri, a nerve- 

 fiber from the olfactory tract ramifying in the gray matter of the bulb (Schafer). 



and they eventually become fibers of the olfactory tract and pass 

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

 in the bulb as they pass backward. 



" 3. The layer of olfactory glomeruli consists of rounded nest- 

 like interlacements of fibrils which are derived on the one hand 

 from the terminal arborizations of the non-medullated fibers 

 which form the subjacent layer, and on the other hand from 

 arborizations of descending processes of the large ' mitral ' cells 

 of the layer above. 



"4. The Layer of Olfactory Nerve-fibers. These are all non- 



