204 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



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 lobe, especially 

 its distal portion, the gyrus uncinatus. 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 move- 

 ments that accompany usually strong olfactory sensations. On 

 the other hand, ablations of these regions are followed by defects 

 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 

 center may lie in the posterior portion of the gyrus fornicatus 

 (6, Fig. 94). 



Aphasia. The term aphasia means literally the loss of the 

 power of speech. It was used originally to indicate the condition of 

 those who from accident or disease affecting the brain had lost in 

 part or entirely the power of expressing themselves in spoken words, 

 but the term as a general expression is now extended to include 

 those who are unable to understand spoken or written language, 

 that is, those who are word-blind or word-deaf. It is usual, there- 

 fore, to distinguish sensory aphasia from motor aphasia. By the 

 latter term is meant the condition of those who are unable to speak, 

 and by sensory aphasia those who are unable to understand the 

 written, printed, or spoken symbols of words. 



Motor Aphasia. A condition of motor aphasia not infrequently 

 results from injuries to the head or from hemorrhage in the region 

 of the middle cerebral artery. The first exact knowledge of the 

 portion of the brain involved seems to have been obtained by 

 Bouillaud (1825) as the result of numerous autopsies. 



