2 ELEMENTARY PHYSIOLOGY. [XIII. 



almost immediately after the auricles con- 

 tract, then the ventricle, and finally the bulbus 

 arteriosus. 



4. Make now a transverse cut through the skin of 

 the frog just below the jaw, and carry the cut as 

 far as the vertebral column ; cut through all the 

 muscles proceeding from the head of the hume- 

 rus and from the part of the sternum left attached 

 to it, to the hyoid bone or to the angle of the 

 jaw. 



Coming up from underneath the angle of the 

 jaw and stretching towards the lower extremity 

 of the hyoid bone will be seen a thin narrow 

 band of muscle and two small white fibres, one, 

 the glossopharyngeal nerve, running along its 

 upper border, the other, the pneumogastric nerve, 

 running along its lower border. Very carefully 

 separate the pneumogastric from the surrounding 

 tissue, and place a loose ligature around it, it 

 will be seen to divide into two branches, the 

 smaller branch, the laryngeal, may be cut through. 

 It will be safer not to attempt to dissect out the 

 pneumogastric close to the heart. 

 The nerve may be ligatured close to the skull 

 (some care is required in doing this) and cut 

 above the ligature. 



Pass an interrupted current through the pneumo- 

 gastric nerve. It is well to place a small piece 

 of thin india-rubber membrane underneath the 

 nerve to prevent contraction of the neighbouring 

 muscles by an escape of current. 



