PRACTICAL CONDUCT OF EXERCISE XII 



149 



on either side of this tongue-guard presses against the anterior edge of the ascending ramus 

 of the lower jaw close ventral (posterior) to the point at which the line v-v (text-fig. 47, a) 

 meets that border of the ramus. The open jaws and cranium are thus kept and supported 

 at the desired angle. 



The apparatus is used as follows : 



Pelvis and hind quarters are set astride the saddle carried by p, text-fig. 46, and the position 

 of the saddle- standard is shifted suitably to the length of the animal. The head is introduced 

 between the sides of the steel plate carried on the yoke-block y, text-fig. 46, so that the 

 tongue-guard t of the steel plate lies in the mouth above the tongue, which it protects. The 

 head is moved down so that the coronary processes of the jaw come to lie against the bottoms 

 of the bays in the steel plate symmetrically either side of the tongue-guard. The apices of 

 the upper canines then lie about 5 mm. from the anterior face of the steel plate. The free 

 top of the tongue-piece lies over epiglottis within the fauces. 



vii. The decerebrator has a strong gut cord or thong (c, text-fig. 46) threaded through 

 a hole traversing the steel plate and the wooden block. The cord's upper end carrying 

 a steel hook projects freely through the hole and above the V-notch in s. The hook is 

 now caught in the snout cord-loop (see ii above) and the thong is drawn tight by pulling on 

 it below where (text-fig. 46) it hangs free under the wooden arch of the decerebrator. The 

 cord is then fixed firmly on the side-cleet 

 provided. The cord thus immobilizes the head 

 in the position given by the steel plate. 



The brass-bound wooden piece, which with 

 its clamp-screw loose has been low to be out 

 of the way of the cord's emergence from the 

 steel plate, is now slid up so as to meet the 

 snout and support it in its V-notch. It is not 

 pushed up so far as to push the head out of 

 the position that has been given it. It serves 

 simply to prevent the slipping or yielding of 

 the head under the knife. 



viii. The knife, of the shape and dimensions 

 given in text-fig. 48, is now taken in the left hand, 

 the operator standing with the animal sidewise 

 to him, its head to his left, i.e. he faces the 

 decerebrator on the side opposite to that looked 

 at in text-fig. 46. Holding the knife vertical, 

 with the bevelled edge of its blade forward, he 

 sets the mid-point of the edge of the blade in 

 the small notch he has marked (see v above) 

 on the mid-line of the skull, the blade truly 

 transverse to the length of the skull. Noting 

 the horizontal line engraved on the side-piece 

 of the steel plate nearest him, he now, without removing the knife-blade from the notch 

 on the skull, adjusts the direction of the plane of the blade so that a continuation of 

 that plane downward will meet the engraved line on the steel plate. The knife under the 



U 3 



9e"^''7'i 



Text-pig. 48. Knife for decerebrator, showing 

 the rounded end-shoulders protecting the 

 cutting edge. 



