CEANIAL NERVES 255 



i. The anterior or hyoidean branch is the smaller 



of the two, and runs down the posterior 



border of the hyoidean arch, 

 ii. The posterior or branchial branch is larger, and 



runs down the anterior border of the first 



branchial arch. 



Press away the medulla from the skull-wall to see the root 

 of the nerve, about an eighth of an inch behind the auditory 

 nerve : slice away the auditory capsule horizontally to expose 

 the nerve in the canal, and then follow the branches along the 

 branchial arches. 



10. The pneumogastric or vagus is a large nerve, which 

 arises by a number of roots from the side of the 

 hinder part of the medulla, the most anterior root 

 being immediately behind and dorsal to that of the 

 glosso -pharyngeal. 



The nerve, formed by the union of these roots, 

 runs outwards and backwards through the skuU- 

 wall, emerging at its hinder end between the cranium 

 and the auditory capsule. It then runs horizontally 

 backwards parallel to the vertebral column, and a 

 short distance to its outer side, lying along the inner 

 wall of the anterior cardinal sinus, and giving off 

 numerous branches. 



Press away the medulla from the skull-wall to see the 

 roots of origin of the vagus. Slice away horizontally the 

 hinder end of the skull to expose the nerve in this part of its 

 course. Lay open the anterior cardinal sinus by slitting up 

 its dorsal wall ; wash out the contained blood, and identify 

 the branches of the vagus running along its inner wall and 

 across its floor. Dissect these branches out, and follow them 

 to their distribution. 



i, The branchial nerves, which are four in number, 

 run backwards and outwards in the floor of the 

 anterior cardinal sinus to the upper ends of the 

 four hinder, i.e. second to fifth, branchial clefts. 



