AOETIC VALVE INCOMPETENCE 53 



The arterial cannula, which will be inserted into the subclavian, should 

 have a nozzle-neck as little narrowed as is compatible with security of liga- 

 tion, and a nozzle-opening well shaped and sloped but also as free as possible. 

 The subclavian will take a nozzle of 2-5 mm. external diam. Freedom of 

 nozzle-channel favours the registration of the pulse-form. 



See that the Hg manometer is also at hand although not attached to the 

 kymograph. You will use it for calibrating the membrane manometer. 



Have at hand the packing-needle with eyelet at its sharp end, also strong 

 scissors and string, for the operation of opening the chest, as in exerc. IV. 

 Also strong wire stylets provided, for passing into the innominate artery and 

 breaking the aortic valve. 



Arrange kymograph gear to allow a speed of travel of recording-surface 

 up to 1-2 cm. per second. 



III. Operation. Place the preparation supine with the hind-limbs extended 

 by clip-weights to the feet, and the forelimbs drawn somewhat away from the 

 sides of the chest and retracted by weights. 



Expose the innominate and left subclavian arteries in the chest by the 

 method followed in exerc. IV (PI. I), modifying that procedure by opening 

 the thorax not farther back than the 5th intercostal space and carrying the 

 excision of the portion of the chest-wall through the top ribs completely to 

 the base of the neck. Beginning with the right 5th space, pass the sternal 

 ligature securing the internal mammary arteries as soon you have cut the 5th, 

 4th, and 3rd right ribs and pass the ligature from the right. The freed flap of 

 chest-wall should be turned to the preparation's right instead of neckward, 

 and retracted to the right with a heavy hook- weight. Take care not to 

 wound the large veins when cutting through the 1st ribs. 



The contents of the top of the thorax being thus bared to view, note (see 

 PI. II, fig. 6) the superior vena cava and the great arterial trunk (innominate) 

 to left of it, springing from the aorta. From the innominate arise (in the cat) 

 left carotid, right carotid, and right subclavian. Lay bare the innominate 

 right up to the origin of its first branch ; for doing so it is well to draw the 

 superior cava to the right by attaching a light clip- weight to the tissue near 

 the vein. 



The innominate artery is about 22-25 mm. long up to its first branch. 

 Pass three threads (PI. II, fig. 6) under the innominate as follows : (1) a 

 thread where the trunk breaks up into its three main branches ; (2) a thread 

 6 mm. lower down the trunk ; (8) a thread round the root of innominate at 

 its origin from the aorta. With threads (1) and (2) tie for each the first bend 

 of a reef-knot, but leave them untightened. With thread (3) make a simple 



