ON THE MAMMALIAN NERVOUS SYSTEM. 517 



(c.) That such bilateral effects, under these circumstances, can be evoked more 

 readily by excitation of the corona radiata than of the cortex. 



Hence, we conclude that, as far as the cortical efferent representation of the lower 

 limb in the Cat and Monkey is concerned, the normal condition is that of 

 unilaterality. (See Chapter VII.) 



(5.) Electrical Changes evoked in the Spinal Cord by Excitation of its Columns. 



Observation of the electrical changes in the dorso-lumbar spinal cord, when 

 evoked by direct excitation of its fibres after severance from the encephalon, has 

 revealed by comparison of the electrical changes produced the proportionate existence 

 of direct and indirect channels in the various columns of the cord. 



We have thus examined the columns so far as they conduct ascending and descending 

 impulses respectively in the Cat and Monkey. This analysis we extended by employing 

 the exclusion method of intervening sections, as an addition to observations on the 

 intact cord. The results show that : 



(a.) In the Monkey a relatively larger number of direct fibres are contained in the 

 lateral column than in the posterior column, the reverse being the case in the Cat. 



(b.) For both classes of impulses and of animals observed we have obtained (a) no 

 evidence of crossing between the lateral columns, (/3) evidence of indirect connections 

 between one posterior column and the lateral column of the same side, (y) evidence of 

 cross connections between the posterior columns. 



(c.) There is no evidence of the existence in the anterior columns of the cord (Cat 

 and Monkey) of any continuous fibres between the mid-dorsal and lumbar regions. 



(d.) The spread of impulses from path to path in the spinal cord appears, in 

 addition to what is stated under (b), to be conditioned as follows : The posterior 

 column fibres spread into other columns more as they ascend than as they descend, 

 whereas the fibres of the lateral column spread in a converse manner. (See 

 Chapter VIII.) 



(6.) The Relations of the Spinal Cord to the Lumbar Nerves. 



We have investigated the relation of the peripheral nerves and their roots to the 

 paths and to the bulbo-spinal centres in the dorso-lumbar region of the spinal cord. 



The investigations consisted in observing (A) the electrical changes produced by 

 exciting the mixed nerves or their roots in the spinal cord when separated from the 

 encephalon, (B) the electrical changes produced by excitation of the divided cord in 

 the spinal nerves, and (C) the excitatory changes produced by stimulation of the 

 spinal centres. 



A. The results obtained by the first method may be grouped as follows : 



(a.) By far the majority of afferent impulses ascend the cord on the same side as 



