ON THE MAMMALIAN NERVOUS SYSTEM. 481 



Efferent Channels of Communication. The efferent path from the encephalon, i.e., 

 cerebrum, is well known as the pyramidal tract, and the fibres composing it are 

 commonly supposed to end in the corpuscles of the anterior horns. As this 

 connection is of the utmost importance, we may be permitted to discuss the point at 

 a little further length. 



The evidence by the degeneration method shows that the principal mass of the 

 pyramidal tract fibres do not run towards the corpuscular elements in the anterior or 

 ventral horn, but towards the posterior or dorsal portion of the nerve centres, thus 

 suggesting that the fibres join rather the field of conjunction than the efferent side. 

 Again, the degeneration method shows clearly that no pyramidal fibres pass directly 

 out into the anterior root. 



Anatomically therefore there is evidence of some structural change in the path 

 where the pyramidal fibre comes into relation with the spinal centres. 



The distribution of the pyramidal fibres in the spinal cord is still so much a matter 

 sub judice, especially after recent work by the histological* methods, that the complete 

 destination of the fibres, when yet at the upper part of the cord, is unknown. 



The existence of efferent fibres (internuncial) connecting each nerve centre with the 

 next and others below it have, like the afferent internuncial system, been surmised to 

 exist from physiological evidence, all anatomical facts being wanting. 



We believe that our previous experiments (see bilaterality, &c.) go to show that 

 such efferent internuncial fibres must be few in number and but feebly differentiated. 



The efferent channels from the spinal nerve centres are the fibres composing the 

 anterior roots. 



Commissural Channels of Communication. Of commissural connection between 

 spinal nerve centres of opposite sides of the cord no certain anatomical proof exists, 

 but the presence of such connection is surmised from the physiological evidence, and 

 is morphologically suggested by many researches, especially those of LOCKHART 

 CLARKE and GOLGI. 



2. Physiology. 



While the spinal nerve centres have been investigated in numerous ways since 

 WuNDTt estimated the delay in the passage of an impulse through them, it is 

 remarkable how little is known with certainty of their functional activity. 



By the galvanometric method we have been able to establish some fundamental 

 considerations on this matter, and, to indicate their bearing, we will first enumerate 

 categorically the facts that have been previously ascertained by various investigators. 



The facts may be conveniently divided under the headings of 



* See particularly C. GOLGI, ' Anatomischer Anzeiger,' 1890, Nos. 13 and 14, and C. SHEEEINGTON, 

 ' Journal of Physiology,' &c. 



t WUNDT, ' Untersnchungen zur Mechanik der Nerven und Nervencentren,' 1876. 

 MBCCCXCI. B. 3 Q 



