434 THE NEEVOUS REGULATION OF THE BLOOD-VESSELS 



junction, where the united ventral vagus forms the plexus gastricus 

 anterior, and the dorsal vagus, the plexus gastricus posterior. Both 

 plexuses are intimately connected with one another by fibers and com- 

 municate with the abdominal gangha of the sympathetic system by 

 direct rami to the plexus suprarenalis. The plexus gastricus ventralis 

 also gives off fibers which pass along the lesser curvature of the stom- 

 ach and eventually ramify upon the pylorus where they unite with the 

 plexus hepaticus. 



It is a well-known fact that the vagi nerves convey musculo- 

 motor and sensory impulses to and from the stomach and the other 

 organs of the abdomen. ^ They do not, however, seem to possess a 

 true vasomotor function. It should be mentioned at this time that 

 the excitation of the vagus frequently produces very decided reduc- 

 tions in the blood supply of the stomach and intestine, which are not 

 due to the inhibition of the heart nor to an active constriction of the 

 blood-vessels, but ^re dependent upon the peristaltic motion invariably 

 ehcited by the stimulation of this nerve. The influence of the inhib- 

 itor action of the vagus upon the heart and blood flow may be avoided 

 by simply stimulating this nerve at any point below this organ or 

 by administering an adequate amount of atropine to paralyze the 

 inhibitor mechanism. The perseverance of these vascular changes, 

 even after these precautionary measures have been taken, must 

 lead us to conclude that the contraction of the gastric and intestinal 

 walls lessens the size of the blood-bed and thus diminishes the blood 

 flow in a perfectly mechanical manner. 



The vagi, however, form a most important afferent path by means 

 of which the organs of the abdomen are connected with the central 

 nervous system. They are concerned, therefore, with the production 

 of numerous reflex actions, such as (a) the inhibition of the heart ^ in 

 consequence of strokes upon the region of the stomach (plexus Solaris), 

 (6) the systemic vasomotor and cardiac disturbances occasioned by 

 chemical and mechanical irritation of the intestine, (c) the referred 

 symptoms accompanying inflammatory reactions in any part of the 

 abdominal cavity, and others. 



Like the vagi, the splanchnic nerves are efferent and afferent in 

 their function. They form the connection between the thoracic and 

 abdominal ganglia of the sympathetic system. Beginning at the 

 ganglion stellatiim, a number of fibers pass downward along the spinal 

 column to be constantly augmented by fibers derived from the differ- 

 ent spinal nerves (Fig. 226). Opposite the thirteenth rib, this nerve, 

 which is known as the thoracic sympathetic, divides into the splanch- 

 nicus major and the sympatheticus abdominahs. The former pierces 

 the diaphragm and passes toward the adrenal body, where it ramifies 

 extensively, forming here the so-called plexus suprarenalis. The lat- 



1 Burton-Opitz, Pfliiger's Archiv, cxxxv, 1910, 205. 



^ As we are here concerned solely with reflexes upon the circulatory system, 

 the accompanying inhibition of the respiratory action is not considered at this time. 



