196 THE CEREBRUM. 



arborizing processes from the granules in the fifth layer and the 

 branches of a few endogenous spindle cells, called the brush cells. 

 The mitral dendrites are on their way to the glomeruli in the 

 second layer. The spindle cells likewise, both large and small, 

 throw their dendritic processes down into the stratum glomeru- 

 losum, where they end in rich tufts or brushes; and their axones 

 penetrate the fourth and fifth layers, enter into the white sheath 

 of the bulb and thence are continued into the olfactory tract. 

 (4) The stratum cellulare, or layer of mitral cell-bodies. The 

 mitral cells have large pyramidal bodies with one axone and rich 

 dendritic processes. The latter arborize through the reticular 

 layer to the glomeruli of the second layer, where they terminate 

 in the form of end-brushes. The axones of the mitral cells run 

 centrally through the granular layer, to which they give off col- 

 laterals, and then turn backward in the white sheath and ulti- 

 mately constitute the olfactory tract. The white sheath incloses 

 a mass of cells derived from the ependymal lining of the ventricle 

 in the embyro. (5) The stratum granulosum is composed of a 

 thick layer of small cell-bodies, "granules," whose processes 

 arborize richly in the granular, cellular and reticular layers. 

 Imbedded in the granular layer are the medullated axones coursing 

 toward the white sheath and the olfactory tract. The function 

 of the granular layer is not understood. The mitral and spindle 

 cells of the olfactory bulb, it should be carefully noted, form the 

 terminal nucleus of the olfactory nerves: the points of contact 

 between them are established in the glomeruli; and the axones 

 of the nucleus constitute the olfactory tract and its stria, which 

 join the bulb to the cerebral hemisphere (Fig. 63). The lateral 

 stria of the olfactory tract runs directly to the uncus, hence we 

 shall study that region next. 



The uncus and crown of the hippocampal gyrus (Figs. 55, 6 1 

 and 62) probably represent the greater part of the lobus pyra- 

 formis of osmatic mammals. It constitutes the chief cortical 

 center of smell. However it is probable that the subiculum, 

 hippocampus, fascia dentata, and anterior end of the gyrus cinguli 

 belong in the cortical area of smell, as all showed arrested develop- 

 ment in two cases of congenital absence of the olfactory bulbs 



