KEGUKGITANT VENOUS PULSE. 329 



does not exist. In extreme congestion, reflux of blood may 

 take place to a certain extent in the external jugular, for this 

 vessel has but two valves, which are not competent to pre- 

 vent regurgitation ; 1 but the chief cause of congestion is 

 due, not to regurgitation, but to accumulation from the pe- 

 riphery, and an obstruction to the flow of blood into the great 

 vessels. 



It is in the internal jugular that the influence of expiration 

 is most important, both from the great size of the vessel in the 

 human subject, as compared with the other vessels, and from 

 the importance and delicacy of the parts from which it collects 

 the blood. At the opening of this vessel into the innominate 

 vein, is a pair of strong and perfect valves, which effectually 

 close the orifice when there is a tendency to regurgitation. 

 These valves have attracted much attention among physiolo- 

 gists, since the discovery of the circulation has made it evi- 

 dent how important they might be in protecting the brain 

 from reflux of blood. When the act of expiration arrests the 

 onward flow in the veins near the thorax, these valves are 

 closed, and effectually protect the brain from congestion by 

 regurgitation. The blood accumulates behind the valves, but 

 the free communication of the internal jugular with the 

 other veins of the neck relieves the brain from congestion, 

 unless the effort be extraordinarily violent and prolonged. 



The above remarks with regard to the influence of expira- 

 tion are applicable to vocal efforts, violent coughing or sneez- 

 ing, or any violent muscular efforts, such as straining, in 

 which the glottis is closed. 



.Regurgitant Venous Pulse. In the inferior animals, like 

 the dog, if the external jugular be exposed, a distention of 

 the vessel is seen to accompany each expiratory act. This is 

 sometimes observed in the human subject, when respiration 

 is exaggerated, and has been called improperly the venous 

 pulse. There is no sufficient obstacle to the regurgitation of 





1 GRAY, Descriptive Anatomy, Philadelphia, 1859, p. 404. 



