24 EXEKCISE V 



vertical. To know the * disparation of the longitudes ' is necessary for 

 reading latent periods, &c. Then run the kymograph on for a cm. and stop it. 



(5) Have ready three mounted ligatures, i. e. cotton threads about 20 cm. 

 long, threaded through 3 curved mounted needles (see exerc. IV) ; they 

 should be so threaded that one end hangs about 2 cm. beyond the needle's 

 eye. Wet them and put them within handy reach on the operation table, 

 along with a dish of Kinger-Locke containing the arterial cannula and 

 * filler-up '. 



(6) Have ready a needle-syringe ; see that its needle is patent, and that 

 its piston fits well. 



II. Operation for Carotid (PI. II, figs. 1, 2, 3, 4). Place the preparation 

 supine. Attach a clip-weight to each foot and set the hind-limbs sym- 

 metrically extended and the forelimbs similarly extended backwards on 

 either side of the chest. See that the animal lies symmetrically : it will 

 tend to lie to one side : obviate this by placing a warm bottle on each side 

 of its chest. 



The operation for exposure of the carotid is the same as that performed 

 in exerc. IV for exposing the vagus nerve in the neck. In the present 

 exercise it is preferably done on the left side, reserving the right side for 

 the vagus. 



Standing on the preparation's right side, make with the scalpel an incision 

 4 cm. long and 1 cm. to left of mid-line of neck from level of cricoid back- 

 wards. Avoid external jugular vein, which lies subcutaneously and lateral, 

 i. e. to the right of the wound on right side of neck. Dissect down along 

 median side of sterno-mastoid muscle. The carotid artery (c) comes into 

 view accompanied by the internal jugular vein, which is smaller than the 

 external jugular, and by the vagus nerve (Vag) (large) and the cervical 

 sympathetic (Sy) (small). The carotid artery lies to the median side of the 

 jugular vein. Note the small thyroid branch from carotid ; it usually 

 springs from carotid at a level near behind the space between cricoid cartilage 

 and the first cartilage ring of the trachea. Expose the artery for 3 cm. 

 from thyroid branch backward and separate from it the nerves and vein 

 without actually touching the vessels or nerves. 



III. Insertion and securing of the cannula and connexion of it with the 

 manometer. With the mounted needles pass three threads round the artery, 

 (1) (PI. II, figs. 4 and 5) at the origin of thyroid artery; (2) (PI. II, 

 figs. 4 and 5) about 6 mm. nearer thorax ; (3) (PI. II, figs. 4 and 5) about 1 cm, 

 lower than (2). Tighten (1) ; make the first noose of a reef-knot with (2), 



