7io 



THE CEREBRAL CORTEX. 



rate of 60 per second ; the two tracings show an identical rate of the 

 waves which indicate successive muscular contractions. 



The circumstance that a muscular response is obtained at the rate in 

 question does not, of course, establish the fact that this rhythm is 

 originated in the cortex itself. For excitation of the corona radiata, 

 after removal of the superjacent motor cortex, or even of the cut 

 spinal cord, produces a muscular response which has a precisely similar 

 character and rhythm. Thus, in Fig. 324, A is the result of rapid 

 stimulation of the cortex, B of the corona radiata, C of the cut spinal 



Fig. 324. — Tracings obtained from the same muscle of a dog, on stimulation of different 

 parts of the motor path. (A) Leg centre in cortex cerebri ; (B) corona radiata, after 

 removal of cortex ; (C) cut spinal cord ; (D) cut motor nerve. The vertical lines 

 (omitted in D) mark seconds. The teeth on the abscissae show the rate of excita- 

 tion. In A the cessation of the excitation is followed by clonic epileptoid spasms 



of the muscle. 



All to be read from left to right. 



cord, and D of the motor nerve, all in the same individual (dog), the 

 same muscle being employed. The rate of stimulation in each case was 

 at least 30 per second, but the response in A, B, and C was only at the 

 rate of about 10 per second. In B and C this rhythm must have 

 become established in the cells of the spinal cord ; in A it may have 

 originated in the cells of the cortex. Or the cortical cells may have 

 responded at the same rate as the excitation, and the change of rhythm 

 may have occurred in the cells of the cord. It is, however, probable 

 that the cells of the cortex respond to rapid or continuous excitation at 

 about the same rate of rhythm as do the cells of the lower centres, since 

 the rhythm of epileptoid contractions, which unquestionably originates 



