HISTOR Y OF THE INVOL UNTA R Y NER VO US S YSTEM 9 



effected through these connector neurons, as represented diagram- 

 matically in Fig. 3, B. 



Further consideration of the cells constituting the dorsal 

 nucleus of the vagus is given in chapter IX. 



DM. 



P.R.G.- 



FIG. 2. THE REFLEX PATHS IN THE CORD. 



A. Of the voluntary system. 



The receptor neurons run in the posterior root, their cells lying in the posterior 

 root ganglion, P.RG. The connector neurons lie in the dorsal horn, D.H., and 

 connect with the excitor neurons lying in the ventral horn, V.H., whose processes 

 run in the anterior root. 



B. Of the involuntary system. 



The receptor neurons run in the posterior root, their cells lying in the posterior 

 root ganglion, P.R.G. The connector neurons lie in the lateral horn, L.H., their 

 processes running out in the anterior root and connecting, as the white ramus 

 communicans, with the excitor neurons lying in the sympathetic ganglia, Sy.G. The 

 processes of the excitor neurons form the grey ramus communicans and run out in 

 the spinal nerve. 



Turning now to the consideration of the involuntary nervous 

 system, can we classify its muscles into morphological groups as 

 in the case of the muscles of the voluntary system, and can we 

 define with equal precision the position of its receptor, connector, 



