104 



THE MECHANISM OF THE CIRCULATION. 



To the finger, both the breadth of the pulse and the apparent 

 diameter of the radial artery is increased by distension of the venae 

 comites. Such being the case, on examining the radial sulcus with the 

 finger, we can speak of 



1. The size or breadth of the band-like swelling, composed of the 

 artery and the veins, which more or less occupy this space. 



2. The tension of the band. By this we mean the sense of 

 pressure necessary to obliterate the calibre of the artery, and stop 

 the pulse. 



3. The condition of the arterial wall, which can be investigated by 

 flattening the artery with the finger and rolling it upon the bone. 



4. The oscillation or wave of expansion. 



FIG. 68.- Section of fore- 

 arm passing through the 

 radial sulcus. Hill, Bar- 

 nard, and Sequeira. 



a, Skin. 



b, Fat. 



c, Deep fascia. 



d, Flexor carpi radialis. 



e, Superficial vein. 



/, Radial artery and its venae 



comites. 



g, Pronator quadratus. 

 h, Styloid process of radius. 



FIG. 69. Superficial view of the radial 

 vessels. Hill, Barnard, and Sequeira. 



a, Venae comites. 

 I, d, Flexor carpi radialis. 

 e, Post. div. radial nerve. 

 e, Radial artery. 



The wave of expansion admits of description in these particulars 

 (1) Frequency; (2) regularity; (3) amplitude of excursion; (4) 

 period of excursion ; (5) dicrotism. 



A radial sphygmogram is a pressure curve, for the movements of the 

 lever of the sphygmograph are produced by the changes in pressure in 

 the vessels which lie in the radial sulcus. The scale by which the 

 ordinates of the curve should be measured is, however, an unknown 

 quantity. The arterial pressure acts not only on the arterial wall, but 

 also on the surrounding tissues; and since the pad of the instrument 

 rests partly upon the venae comites, not only the arterial tension, but 

 any turgidity arising from venous congestion, affects the height of the 

 sphygmographic curve. 1 That this is so, is shown by the effect of 

 compression of the veins of the arm. 



In Fig. 70, tracing 1, the whole of the upper arm at the point (A) was 

 compressed by the hands of the observer ; at the point (B) the compression 



1 Hill, Barnard, and Sequeira, Journ. PhysioL, Cambridge and London, 1897, vol. xxi. 

 p. 148. 



