466 



GENERAL BIOLOGY 



means (as well as by the opposite one of observing the 

 paralysis produced by local injuries) the great motor 



area that traverses both 

 hemispheres (m, of fig. 

 264), has been carefully 

 explored. The definite- 

 ness of the responses to 

 stimulation upon these 

 centers has been aptly 

 compared to that of the 

 tones of a piano that 

 result when certain keys 

 are struck. If, however, 

 the motor center for the 

 leg or arm be stimulated 



FIG. 264. Diagram of localization of functions Vio-mie-nVi^t-^ tVi#* 



in the cerebrum. M, medulla. C, cerebel- in one Hemisphere 

 lum. m, the great motor area of the hemis- I^-U ~f +l-i^ rtV.p.-r cirl^ nf 

 phere Vith a few of the control centers limt> ol tne Otner Side C 

 approximately indicated: n, center for f i^ P "hnrl v will mnv^' for 

 movements of the leg; o, for arm; p, for face; T ' nt 3a y W11J LOVC, 1 

 a, for head; r, for organs of speech; t. center +-L mr+nr fi"hArc r>f tVif 

 for hearing ("brain deafness" may result tne motor HDerS OI tne 

 from its injury) ; , for sight ; v, for smell. g rea t tract B of figure 



261, (the "crossed pyramidal" tract) in the medulla, cross 

 over to the opposite side of the body from the one in which 

 they originate. For this reason, also, great injury to one 

 hemisphere produces paralysis of the opposite side of the 

 body. Conversely, the seat of injury, hemorrhage, etc., 

 within the brain may often be located by observing what 

 portions of the periphery of the body are paralyzed or ab- 

 normal in their action. 



Study 60. Demonstration of the functions of some of the 

 principal parts of the nervous system in the frog. 



Materials needed: Living frogs, some of them prepared 

 for this study several hours in advance of need (in order to 

 allow time for recovery from the shock of the operations) as 



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