CHAP, iv.] THE VASCULAR MECHANISM. 237 



Careful tracings of the great veins in the neighbourhood of the 

 heart shew elevations and depressions, which appear due to the 

 variations of endocardiac pressure, and which may perhaps be 

 spoken of as constituting a ' venous pulse,' though they have 

 a quite different origin from the venous pulse just described 

 in the salivary gland. In such a pulse it is the depression of 

 the wave, not the elevation, which corresponds to the systole 

 of the ventricle, the pulse-wave is the negative of the arterial 

 pulse-wave ; the matter however needs further study. In cases 

 again of insufficiency of the tricuspid valves, the systole of the 

 ventricle makes itself distinctly felt in the great veins ; and an 

 expansion travelling backwards from the heart becomes very 

 visible in the veins of the neck. This, in which the elevation of 

 the wave like that of the arterial pulse-wave corresponds to the 

 ventricular systole, is also spoken of as a venous pulse. 



Variations of pressure in the great veins due to the respiratory 

 movements are also sometimes spoken of as a venous pulse ; the 

 nature of these variations will be explained in treating of respi- 

 ration. 



