THE OLFACTORY BULB. 421 



which also terminate in the same manner in the gray substance. 

 The association fibers form the bulk of the medullary rays. 



On examining a vertical section through one of the cerebral 

 convolutions a number of successive striations may be seen. These 

 are more or less distinct, according to the region, and consist of 

 strands of medullated nerve-fibers between the layers of cells, and 

 parallel with the surface of the convolution. The most superficial 

 form a layer of tangential fibers. Between the molecular layer and 

 the layer of small pyramidal cells is the striation of Bechtereff and 

 Kaes, and in the region of the large pyramidal cells the striation of 

 Baillarger (Gennari) corresponding to the striation of Vicq d'Azyr 

 in the cuneus. In figure 336 the medullary substance is seen 

 below, \vith rays, composed of parallel bundles of fibers, passing 

 upward into the gray substance ; in reality these fibers penetrate 

 much higher than is shown in the illustration. 



D. THE OLFACTORY BULB. 



The olfactory bulb is composed of five layers, which are espe- 

 cially well marked on its ventral side : first, the layer of peripheral 

 nerve-fibers ; second, the layer of olfactory glomeruli ; third, the 

 stratum gelatinosum, or molecular layer ; fourth, the layer of pyr- 

 amidal cells (mitral cells) ; and, fifjth, the granular layer with the 

 deeper nerve-fibers. 



The layer of peripheral fibers is composed of the nerve- 

 bundles of the olfactory nerve which cross one another in various 

 directions and form a nerve-plexus. The glomerular layer con- 

 tains peculiar, regularly arranged, round or oval, and sharply defined 

 structures, which were first accurately studied by Golgi. They are 

 known as glomeruli (from 100 [J. to 300 /JL in diameter), and are in 

 reality complexes of intertwining telodendria. As we shall see, 

 the epithelial cells of the olfactory region of the nose must be 

 regarded as peripheral ganglion cells and their centripetal (basal) 

 processes as neuraxes. The telodendria of these neuraxes, together 

 with those of the dendrites from the mitral or other cells, come in 

 contact with each other within the olfactory glomeruli. The molec- 

 ular layer consists of small, spindle-shaped ganglion cells. Their 

 neuraxes enter the fifth layer and their short dendrites end in ter- 

 minal ramifications in the glomeruli. The mitral cells give off 

 neuraxes from their dorsal surfaces which also enter the granular 

 layer, but the majority of their dendrites break up into terminal 

 ramifications in the olfactory glomeruli, as just described. The 

 granular layer (absent in the illustration) is made up of nerve-cells 

 and nerve-fibers ; but, aside from these, we find also large numbers 

 of peculiar cells with a long peripherally and several short centrally 

 directed dendrites. No neuraxes can be demonstrated in these 



