THE CENTRAL NERVOUS SYSTEM. 



325 



FIG. 349. 



The protoplasmic processes of the mitral cells extend ven- 

 trally and terminate in two ways, as shown by the investiga- 

 tions of Golgi, Ram6n y Cajal, Retzius, and others. In addition 

 to the apical fibrils, lateral processes diverge and terminate in 

 free arborizations 

 within the ventral por- 

 tion of the gray mat- 

 ter. The apical 

 processes take part 

 in the formation of 

 (4) the olfactory 

 glomeruli, peculiar 

 masses (.05-. 3 mm.) 

 composed of dense 

 interlacements of 

 terminal ramifications 

 of the apical pro- 

 cesses sent out by 

 the mitral cells and of 

 the olfactory nerve- 

 filaments. The 

 axis-cylinder pro- 

 cesses of the mitral 

 cells pass dorsally and 

 become continuous 

 with nerve-fibres of 

 the medullary ring ; 

 during their course 

 they give off recur- 

 rent collateral 

 branches. 



The layer of olfac- 

 tory glomeruli is 

 followed by (5) the 

 stratum of olfac- 

 tory nerve - fibres. 

 These are non-med- 

 ullated, and arise in 



the olfactory cells of the Schneiderian membrane, whence they 

 pass into the cranium and end in arborizations included within 

 the olfactory glomeruli, to whose formation they thus con- 

 tribute. The exterior of the olfactory bulb is invested by a layer 

 of pia broken by the passage of the nerve-fibres and the blood- 

 vessels. 



Sagittal section of part of olfactory bulb of young rabbit, stained 

 after Golgi's silver method : m, mitral ganglion-cells from which 

 pass axis cylinder processes (a), sending off recurrent collateral 

 branches (r) and protoplasmic processes (f) ; h, horizontal 

 processes extending tangentially ; g, glomeruli from whose com- 

 plex of nerve-fibrils pass olfactory nerves (<?) ; n, filaments as- 

 cending from mucous membrane. (After Retzius.) 



