42 Journal of Comparative Neurology. 



of the striatum with the nucleus thaeniae which makes up the 

 wall of the preoptic recess (Fig. 20). The cells of this nucleus 

 closely resemble those of the same nucleus in Acipenser. They 

 are fusiform or stellate cells having central processes to the cavity 

 and their dendrites spread widely. The nucleus on the whole 

 appears so much like the mammillare, or that part of the in- 

 ferior lobes which surrounds the postoptic recess, that in study- 

 in ^ sections the optic chiasma appears to be only an interrup- 

 tion in a continuous nucleus. The neurites of these cells in 

 part pass backward over the chiasma into the inferior lobes and 

 in part pass dorsad to join the tractus olfacto-habenularis. These 

 fibers are dispersed in the wall of the thalamus until they are 

 about to meet that part of the tract coming from the olfactory 

 area, when they appear as a distinct bundle forming the caudal 

 border of the tract. I have not traced fibers to the nucleus 

 thaejiiae from- the olfactory lobes, but suppose that such fibers 

 exist. 



d. Lobus olfactorius. 



The olfactory lobe shows a very low order of differentia- 

 tion. Cells and fibers are not gathered in distinct zones, al- 

 though the cells are more numerous near the cavity. In hae- 

 matoxylin sections the glomeruli are prominent and appear to 

 be sharply marked off from one another. The study of Golgi 

 sections shows that this apparent separateness of the glomeruli 

 is due entirely to the arrangement of the olfactory fibers in 

 bundles and is not dependent in any way upon the form or dis- 

 position of the cells of the lobe. In fact, many of the bodies 

 which appear to be glomeruli are no more than cross sections of 

 large bundles of olfactory fibers. 



The olfactory fibers as they enter the lobe gradually break 

 up in the course of these large bundles which are penetrated by 

 the dendrites of cells. These bundles of branching fibers with 

 the dendrites which pierce them form the glomeruli (Fig. 19). 

 A single glomerulus is thus sometimes of great size, running 

 through the outer part of the lobe. The dendrites which enter 

 into the formation of these glomeruli come from numerous cells 

 which lie in all parts of the lobe, either near the central cavity 



