CHAP. II ] 



A NERVOUS SYSTEM. 



45 



then, in order to complete our mental survey of the path 

 of a stimulus wave through such a nervous arc as is called 

 into play in one of the higher animals during the perform- 

 ance of a ' reflex ac- 

 tion,' it only remains 

 to consider the modes 

 of connection exist- 

 ing between the 

 several cells of 

 sensory groups and 

 of motor groups, 

 together with the 

 kinds of communica- 

 tion existing between 

 these two orders of 

 nerve units. 



4. Between the 

 contiguous cells of a 

 motor and perhaps 

 also of a sensory 

 group, union is 

 brought about in 

 some cases by means 



, FIG. 14. Motor Nerve Cells connected by inter- 



OI a SllOrt Simple cellular processes (6, 6), and giving origin to outgo- 



intercellular PrOCeSS ing fibres ( c > c > c < and a )- 4 - Multipolar cell contain- 

 '' ing much pigment around nucleus. Diagrammatic. 



such as we see repre- (Vogt.) 

 sented in figs. 1 and 



14. But whether this is the most frequent means of union, 

 or whether, in the majority of cases, especially amongst 

 sensory groups, it is not rather by the inosculation of the 

 rootlets of ramifying processes (with the possible interme- 

 diation of the neuroglia) we cannot at present say. There 

 is reason to believe that both modes of union may exist. 



5. The cells of a sensory group are united with the 



