136 MR. T. WHARTON JONES ON RYTHMICAL CONTRACTILITY OF VEINS OF THE BAT. 
ti-actility of veins, supported by the presence of valves, is called forth to promote 
the flow of blood in the wings, which, on account of their extent, are, as regards their 
circulation, in a considerable degree, though not entirely, beyond the sphere of the 
heart’s influence. 
I may take this opportunity to mention that I have also found the veins of the 
mesentery of the Mouse destitute of rythmical contractility. 
Explanation of the Plates. 
PLATE IV. 
Fig. 1. A vein with a complete valve. In this figure an attempt has been made to 
represent the backward eddy of blood-corpuscles into the sinuses of the 
valve, at the time the blood issues from the narrow valvular opening into 
the wide part of the vein beyond. 
Fig. 2. A vein with a valve close to the entrance of a large branch. 
Fig. 3. An artery and vein over which pressure had been applied. The artery is 
seen constricted at intervals, above and below the place of pressure a. The 
vein is not constricted, but there is seen, at the place where the pressure 
was applied, a grayish granular deposit of lymph within the vessel, giving 
rise to the appearance of constriction by narrowing the stream of blood. 
Fig. 4. Representation of the case in which the artery, at the place pressed on, was 
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 appeared as much so at first sight. 
In this case the channel of the vein was much narrowed by a deposit of 
lymphy matter on either side within the vessel. 
Fig. 5. This represents an artery (a) and a vein {v), with an accompanying nerve {n) 
lying between the two, as seen with a magnifying power of about 3/0 
diameters; immediately after being separated, by dissection under the 
simple microscope, from a small piece cut out of the living web. The 
cellular sheath was detached along with the two layers of skin. 
The artery is at one place tonically constricted, and there the middle 
coat is seen to be thicker. 
The difference in the general aspect of the fibres of the middle coats of 
the two vessels may be recognised. 
PLATE V. 
This represents a portion of the vascular network of the web of the Bat’s wing, as 
seen under a low magnifying power. The arteries are observed to anastomose with 
each other, and the veins with each other ; but nowhere are the arteries and veins 
seen to communicate directly. The only communication, it is to be observed, is 
through the medium of the capillaries. 
