INNERVATION OF HEART AND BLOOD-VESSELS 559 



near the line between the angle of the jaw and 

 the auricle are four nerves (Fig. 73) : (1) The 

 hypoglossus. This nerve is superficial. Near 

 their emergence from the skull it is the lowest 

 of the nerves, but later, the uppermost. It crosses 

 the remaining nerves and the blood-vessels, and 

 passes forwards and inwards towards the tongue. 

 (2) The glosso-pharyngeus, which soon turns for- 

 wards beneath the hypoglossus parallel to the 

 ramus of the jaw. (3) The vagus, and (4) the 

 laryngeus, the two lying almost parallel in the line 

 between the angle of the jaw and the auricle. 

 The laryngeus rests on the petrohyoid muscle, and 

 passes upwards and inwards beneath the arteries 

 towards the larynx. The vagus runs at first 

 along the superior vena cava to the auricle ; a 

 branch is given off to the lungs. Clear the vagus, 

 tie a silk thread around the nerve and sever the 

 nerve on the cranial side of the ligature, so that 

 the peripheral stump can be placed on the elec- 

 trodes for stimulation. Divide the laryngeal 

 branch. Keep the preparation moist with nor- 

 mal saline solution. 



Stimulation of Cardiac Inhibitory Fibres in 

 Vagus Trunk. Arrange the inductorium for 

 weak tetanizing currents. In the primary circuit 

 place the electro-magnetic signal. Expose the 

 heart. Place it in the heart-holder. Let the 



