THE CRANIAL NERVES 83 



peculiarly sinuous course, close to the middle 

 line and between the geniohyoid and hyoglossus 

 muscles, to the base of the tongue, which it 

 enters and in which it ends. It supplies a petro- 

 hyoid muscle, and the mucous membrane of the 

 pharynx and tongue. 



TJie exposure of the first part of the above nerve is lest performed 

 from the side, and is much facilitated by distending the oesophagus 

 and pharynx with a cork or roll of paper. Its course along the 

 floor of tJie mouth to the tongue should be dissected from the 

 ventral surface. 



10. The pneumogastric or vagus nerve arises, as already 

 noticed, in common with the glossopharyngeal. It 

 leaves the skull by the same aperture as the ninth 

 nerve, and immediately outside the skull presents a 

 ganglionic enlargement : it gives off dorsal branches to 

 the muscles of the back, and then runs backwards and 

 downwards round the side wall of the pharynx, running 

 along the hinder border of the fourth division of the 

 petrohyoid muscle ; behind this muscle it divides into 

 its main branches, which are as follows : 



i. The ramus laryngeus or recurrens loops round 

 the posterior cornu of the hyoid and round the 

 pulmocutaneous artery close to its origin from 

 the aortic trunk : it then passes inwards, dorsal 

 to the artery, to the middle line, where it ends 

 in the larynx. 



ii. The ramus cardiacus passes dorsal of the pul- 

 monary artery to the interauricular septum of 

 the heart, and to the sinus venosus. 

 iii. The rami pulmonales follow the course of the pul- 

 monary artery to the lung, in which they end. 

 iv. The rami gastrici, usually two in number, run 

 through the partial diaphragm formed by the 

 anterior fibres of the obliquus internus muscle, 

 and end in the walls of the stomach. 



The dorsal portions of the aeveral branches of the pneumogastric 

 nerve are best exposed from the side ; to see them properly, the 

 shoulder girdle and fore limb must be removed and the cesophayus 



