THE CRANIAL NERVES. 93 



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 ganglionio 

 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 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 to 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 

 pulmonary 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 several 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 cesophagus 



well distended : the terminal branches must be dissected from the 



ventral surface. 



IV. The Cranial Portion of the Sympathetic Nervous 

 System. 



The main sympathetic trunk of each side extends forwards in 

 front of the first ganglion, and enters the skull at the foramen 

 in the exoccipital bone through which the glossopharyngeal 

 and pneumogastric nerves pass out : it is connected with *the 

 pneumogastric nerve, and then runs forwards within the skull to 

 the Gasserian ganglion of the trigeminal nerve, in which it ends. 



