THE BRAIlSr OP MAMMALS AND THE OLFACTORY APPAKATTJS. 213 



it is designated as the spatium olfactorium {olfactory area, or espace quadri- 

 latere of Br oca). 



To this entire apparatus there is added posteriorly the cortical area, or 

 iield, of the olfactory apparatus, which has been designated, on account of its 

 shape, as the lobus pyriforviis. Mesially, this pyriform lobe passes directly 

 over into the territory of the gyrus hippocampi. 



The long fissura lirnbica separates the olfactory brain from the remain- 

 ing pallium. 



The fibers of the olfactory nerve dip into the bulbus. A section through 

 the bulbus reveals a distinct separation of the tissues into layers. As would 

 be expected, the fibers of the olfactory nerve lie most externally. Then 

 follows a grayish-white zone, in which, even with the naked eye, there are 

 visible numerous small balls, the glomeruli olfactorii; it is known as the 

 layer of the glomeruli. Within this lies the gray layer of ganglionic cells, 

 which then gradually passes, by means of a "granular zone," over into the 

 olfactory medulla. A delicate extension of the lateral ventricle reaches 

 into the bulbus. The ventricular epithelium borders immediately upon the 

 layer of medullated fibers. 



Investigations by Golgi, S. and P. Ramon y Cajal, and those b.)' 

 GeTiucMen and Kblliker have made us familiar with the elements of these 

 layers, and with the very interesting connection of some of these elements 

 with the fibers of the olfactory nerve. 



The fibers of the olfactory nerve are no other than the centrally directed ter- 

 minal processes of the sense-cells of the olfactory mucous membrane. This fact has 

 already been referred to while describing the embryology. 



After these fibers have passed the cribriform plate of the ethmoid and arrived 

 at the ventral surface of the bulbus, they undergo repeated decussations, and then 

 sink into the substance of the brain. There each neuraxon immediately breaks up 

 into a delicate terminal arborization. The arborization meets with the thick branches 

 of a dendritic process, which is similarly branched, and both varieties of fibers, which 

 lie in immediate contact with one another, together form n roundish complex: the 

 glomerulus olfactorius. 



The dendritic process arises from a ganglionic cell, which gives off similar proc- 

 esses in abundance. Only one of them constantly enters into the described relation 

 with the olfactory nerve-fibers. Each of these cells of the brain is connected with 

 quite a number of olfactory fibers, Such cells, varying in form and size, lie in large 

 numbers in the gray layer under the glomeruli. Each sends its neuraxon centrally; 

 it may be followed as far as the layer of medullated fibers. At times it gives off 

 collaterals on the way. Here is a good example of what was spoken of in the chapter 

 on the combination of the tissues of the central organs. The primary and the sec- 

 ondary olfactory pathways are seen directly before you, and it is recognized that 

 the connection is brought aboxit through the splitting-up of the neuraxon of the 

 primary path^^'ay and its contact with the dendritic processes from the secondary. 



A number of other elements (the nervous nature of which is still in doubt) 

 were also found in the cortex of the alfaotory bulb. Between the cells mentioned and 



