222 CIRCULATION OF THE BLOOD. 



also slides horizontally. Near its base it is bent twice at 

 right angles, so that the upper part on which the block slides 

 is not in the same line with the lower part. Consequently the 

 rod, while still remaining horizontal, can be moved in four 

 different ways. It can be shortened or lengthened, heightened 

 or lowered, rotated round its own axis, rotated round the axis 

 of the stem, or moved from side to side without change of 

 direction. It ends in a kind of forceps the blades of which, 

 when kept closed by the adjusting screw, seize upon the head 

 of a cat or rabbit in such a manner as to hold it firmly without 

 inflicting the slightest injury. The neck of the animal rests 

 on a cylindrical cushion, covered with water-proof cloth, and 

 the rest of the body on a mattress of similar material. Along 

 the edges of tlue board there are convenient attachments for 

 the extremities. 



The preparation of the crural artery is even more simple than 

 that of the carotid. The skin having been divided in a line 

 leading from the middle of Poupart's ligament towards the inner 

 side of the knee by first pinching up a fold of skin as above 

 directed, the pulsation of the artery is felt by the finger in the 

 hollow between the adductor muscles and those which cover the 

 femur. The sheath of the vessels having been exposed from 

 Poupart's ligament downwards, the vein and crural nerve are 

 seen, the artery lying behind and to the oute/side of the former. 

 On drawing the vein inwards it is easily got at, and must be 

 prepared from the origin of the arteria prof undo, close to Pou- 

 part's ligament, nearly to the point at which it enters the ad- 

 ductor ; first giving off the arteria saphena, which accompanies 

 the saphenous nerve and veins. The lower of the two circum- 

 flex arteries which are given off within a short distance from 

 the profunda must be tied doubly and divided between the liga- 

 tures, as it is desirable to place the clip as high as possible. 

 In the dog or cat, the operation is equally simple, but requires 

 more time on account of the greater abundance of fat in these 

 animals. 



The canula having been inserted, the next step is to bring 

 the artery into communication with the manometer. The clip 

 on the artery remaining closed, that on the stem of the canula 

 is opened for a couple of seconds. At once the soda solution 

 fills the canula and passes out \>y its open branch. In doing 

 this, great care must be taken not to allow the solution to flow 

 into the wound. Air bubbles, if they exist, are got rid of by 

 passing a thin rod of whalebone into the canula, which must 

 then be closed by means of the terminal clip. All being now 

 ready, the stem of the canula is finally opened, and the clip re- 

 moved from the arterv. The mercurial column at once begins 

 to oscillate ; but no record should be taken until a minute or 

 two have elapsed, for it often happens that a small quantity of 



