CIRCULATION OF THE BLOOD. 559 



ing along these vaso-dilator nerves inhibit the local ganglia in the walls 

 of these vessels and thus lead to relaxation of the muscular fibres of the 

 vessels and to their consequent dilatation. Their modus operandi may 

 thus be regarded as similar to that of the pneumogastric nerves, since 

 in both cases the motor ganglia are inhibited and the muscular fibres in 

 the walls of the organs of circulation relax (Fig. 236). 



Fig. 236.— Diagrammatic Plan of the Cardiac-Nerve Mechanism, after • 

 Carpenter. (Yeo.) 



The direction of the impulses is indicated by the arrows. Both right and left sides of the cut are used 

 to show one complete lateral half of the fibres. 



* 



Finally, to recapitulate, the pulse and blood pressure may be modi- 

 fied by the following causes (Lauder-Brunton) : — 



We have now to follow the blood in its course through the body and 

 consider the changes which it undergoes in the different organs and tis- 

 sues. It was seen that the circulation might be divided into two sys- 

 tems, the greater and lesser. The changes which the blood undergoes in 

 the latter, the pulmonary system, will be considered first. 



