PEACTICAL CONDUCT OF EXERCISE IV 137 



In addition to them for this exercise there are wanted : 



(1) Ordinary druggist's glass syringe of about 20 c.c. capacity. 



(2) Glass U-tube as manometer mounted on wood held vertical by chemical clamp and 

 standard, glass T-piece, and glass cannula for pericardium (PI. I, fig. 4) and three pieces of 

 rubber tubing, one connecting T-piece with manometer, the other two connecting T-piece 

 with cannula and syringe respectively. The manometer contains Ringer-Locke. 



2. Procedure for providing decapitate ^preparation} 



(1) The animal (cat) is deeply anaesthetized with chloroform -ether mixture. 



(2) An ordinary small sharp packing-needle threaded with string is passed horizontally 

 through the upper lip across the labial fissure, and the string tied in a short loop giving less 

 than 1 cm. play. 



(3) The animal is then laid supine on the operating table with limbs extended 

 symmetrically by clip-weights attached to feet, and a warm bottle either side of the trunk 

 to keep the supine posture symmetrical. The hexagonal-sided ribbed glass bottles in which 

 chemicals are supplied serve the purpose well because they do not slip. The head and 

 neck are kept straight and extended by hooking to the string muzzle-loop a weight (150 grm.). 

 The administration of the chloroform-ether is continued freely. 



(4) A short lengthwise median incision is made over the cricoid region, and one edge 

 of it retracted by a light clip-weight. Each common carotid is ligated close posterior to its 

 thyroid branch, and a short-shanked tracheal T-cannula (glass) is inserted into larynx close 

 below vocal cords and tied in. The side-branch of tracheal cannula has a 1 cm. bit of 

 rubber tube on its end and tie-clip, making the size of the open end of tube adjustable. The 

 animal is then placed prone, with warm water-bottle under pelvis ; this, by raising the 

 abdomen somewhat from the table, avoids the embarrassment of respiration and circulation 

 liable in the prone position. The string weights are removed from the fore-paws and the 

 fore-limbs flexed at elbow and shoulder, relieving the chest from pressure. A lengthwise 

 incision is then made through the skin over occiput and for some 5 cm. farther back, and 

 across it a transverse incision at level of the atlas. The prominent wing-like transverse 

 processes of the atlas vertebra are felt for and deep side-incisions are carried through the 

 neck muscles at the level of the posterior edges of these transverse processes. The large 

 beak-like spinous process of the axis is then nipped off with the bone-pliers. With a 

 packing-needle about 15 cm. long a strong string is passed right across ventrally close 

 under the body of the axis between the trachea and oesophagus on the one hand and the 

 vertebral column on the other, and just behind the transverse processes of atlas. The string 

 is tied as tightly as possible around the vertebral column ; it lies in the cross-cut. By it 

 the vertebral arteries are occluded where they pass (see below, p. 148, text-fig. 47) from trans- 

 verse process of axis to transverse process of atlas. A single twist for the first loop of the 

 reef-knot is better than a double twist, because when pulled it sinks better and more closely 

 compresses. The string should be thick, strong, and soft. It is not cut short off after tying, 

 its ends being left for looping over a branch arm from a vertical support when the prepara- 

 tion is later removed to the student's experiment table. 



(5) To decapitate, the head is held flexed by the left hand while with the right a Liston 

 double-edged amputation knife of 12 cm. blade-length is passed vertically down in the 



^ Sherrington, Jnl. of Physiol, vol. xxxviii, p. 375 ; 1909. 

 M$l T 



