218 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



of nerve cells of the olfactory lobe, the mitral and brush cells (C). 

 The axons of these cells pass toward the brain in the olfactory tract. 

 Three bundles of these fibers are distinguished: (1) The precommis- 

 sural bundle, the fibers of which terminate in part in nerve cells sit- 

 uated in the tract itself, but, for the most part, enter the anterioi 

 commissure and pass to the same or the opposite side, to end in the 

 hippocampal lobes or other gray matter belonging to the rhinen- 

 cephalon. (2) The mesial bundle, the fibers of which terminate 

 in the gray matter adjacent to the base of the olfactory tract, 

 the tuberculum olfactorium, whence the path is probably continued 

 by other neurons to the region of the hippocampal lobe. (3) The 

 lateral tract, whose fibers seem to pass to the hippocampal lobe of 

 the same side. According to Van Gehuchten,* none of the fibers 

 of the anterior commissure arise from the nerve cells in the olfactory 

 bulb. He considers that the fibers in the olfactory portion of this 

 commissure constitute an association system connecting the olfac- 

 tory lobe of one side with the olfactory bulb of the other side. 



The Cortical Center for Smell. So far as the histological 

 evidence goes, it tends to show that the chief cortical termination 

 of the olfactory paths is found in the hippocampal convolution, 

 especially its distal portion, the uncus. The experimental evi- 

 dence from the side of physiology points in the same direction. 

 Ferrier states that electrical stimulation in this region is followed 

 by a torsion of the lips and nostrils of the same side, muscular 

 movements that accompany usually strong olfactory sensations. 

 On the other hand, ablations of these regions are followed by de- 

 fects in the sense of smell. The experimental evidence is not very 

 satisfactory, owing to the technical difficulties in operating upon 

 these portions of the brain without at the same time involving 

 neighboring regions. There is some clinical evidence also that 

 lesions in this region involve the sense of smell. Thus Carbonieri 

 records that a tumor in this portion of the temporal lobe occa- 

 sioned epileptic attacks which were accompanied by nauseating 

 odors. 



The Cortical Center for Taste Sensations. Practically 

 nothing definite is known concerning the central paths and cortical 

 termination of the taste fibers. The course of these fibers in the 

 peripheral nerves has been much investigated and the facts are 

 mentioned in the section upon " special senses." It is usually 

 assumed, although without much decisive proof, that the cortical 

 center lies also in the hippocampal convolution posterior to the 

 area of olfaction. Experimental lesions in this region, according 

 to Ferrier, are accompanied by disturbances of the sense of taste. 

 On embryological grounds Flechsig supposes that the cortical 

 * Van Gehuchten, "Le Nevraxe," 6, 191, 1904. 



