134 
MR. T. WHARTON JONES ON RYTHMICAL 
actually not so much constricted as above and below, though, on account of the 
narrowness of the stream of blood from the presence of the lymphy deposit, it ap- 
peared as much so at first sight (fig. 4). 
Having subjected the web to the galvanic influence from a single pair of plates, I 
found all the smaller arteries of the part in a state of considerable tonic constric- 
tion, but the larger arteries constricted in a less degree. The effect of galvanism on 
the veins appeared to be to render their rythmical contractions somewhat more 
brisk, they having been previously rather languid. On cutting a vein across, 1 did 
not observe tonic constriction of it, any more than in the Frog. 
After the application of a drop of Vinum opii to the web, the veins were found 
dilated as well as the arteries, and their rythmical contractions appeared to be sus- 
pended. 
It has been stated by an authority not liable to err, that, on mechanical irritation, 
both artery and vein of the Bat’s web gradually contract and close, and, by and by, 
dilate wider than before. And, again, that in Bats, contraction of veins is quite as 
well marked as that of arteries. 
These statements, it will be observed, imply tonic contractility of the veins. 
Notwithstanding my attention has been repeatedly directed to the point, I have 
not, as previously stated, been able to observe unequivocal evidences of tonic con- 
tractility of veins, in addition to their rythmical contractility. For this reason, I 
cannot help venturing on the supposition that Mr. Paget* must have made his 
statements either from a hasty and imperfect observation of the proper rythmical 
contractions of the veins ; or, seeing that in rythmical contraction of the veins the 
constriction is never to closure, like that of the arteries, under some such misappre- 
hension as to the nature of the vessel observed, as he certainly must have laboured 
under when he supposed that arteries and veins of the second and third order open 
directly into each other without any intermedium of capillaries. 
The arteries and their subdivisions anastomose freely with each other, forming a 
network all through the web, the meshes of which go on to diminish towards the 
free margin. Each artery and each subdivision of an artery is closely accompanied 
by a vein ; and these veins, like the arteries they accompany, anastomose with each 
other. But it is to be remarked that nowhere do the arteries and veins directly 
communicate. The only communication is the usual one through the medium of 
capillaries. The capillaries, the walls of which are destitute of contractility, receive 
the blood from small arterial twigs which arise from the arterial network, and return 
it to the venous radicles which open into corresponding veins. These arterial twigs, 
capillaries and venous radicles, form networks within the meshes of the great vas- 
cular network, and a looped network at the margin of the web-f- (Plate V.). 
The observations recorded in the preceding pages were made principally with 
* Lectures on Inflammation at the Royal College of Surgeons in 1850. 
t I shall have occasion to treat of this point more in detail in a paper on the state of the blood and the 
blood-vessels in inflammation of the web of the Bat’s wing. 
