462 



THE CRANIAL NERVES. 



Fig. 152. 



tioned motor nerves. It becomes, consequently, after emerging 

 from the cranial cavity, a mixed nerve ; and has, accordingly, in 

 nearly all its branches, a double distribution, viz., to the mucous 

 membranes and the muscular coat of the organs to which it belongs. 



The ordinary sensibility of the pneu- 

 mogastric nerve, however, as all experi- 

 menters have observed, is exceedingly 

 dull, in comparison with that of the other 

 sensitive cranial nerves. We have often 

 divided this nerve in the middle of the 

 neck, without any distinct manifestation 

 of pain being given by the animal ; and 

 though Bernard has found that at some 

 times its sensibility is well marked, while 

 at others it is very indistinct, he is not 

 able to say upon what special physio- 

 logical conditions this difference depends. 

 While the pneumogastric, however, is 

 decidedly deficient, as a general rule, in 

 ordinary sensibility, it possesses, as we 

 shall see hereafter, a sensibility of a pecu- 

 liar kind, which is exceedingly important 

 for the maintenance of the vital func- 

 tions. 



In passing down the neck, this nerve 

 sends branches to the mucous membrane 

 and muscular coat of the pharynx, oeso- 

 phagus, and respiratory passages. Among 

 the most important of these branches are 

 the two laryngeal nerves, viz., the supe- 

 rior and inferior. The superior laryngeal 

 nerve, which is given off from the trunk 

 of the pneumogastric just after it has 

 emerged from the cavity of the skull, 

 passes downward and forward, penetrates 

 the larynx by an opening in the side of 

 the thyro-hyoid membrane, and is distributed to the mucous mem-: 

 brane of the larynx and glottis, and also to a single laryngeal mus- 

 cle, viz., the crico-thyroid. This branch is therefore partly mus- 

 cular, but mostly sensitive in its distribution. The inferior laryngeal 

 branch is given off just after the pneumogastric has entered the 



Diagram of PNEUMOGASTRIC 

 NERVE, with its principalbrauclies. 

 1. Pharynireal branch. 2. Supe- 

 rior lary n^eal. 3. Inferior laryu- 

 freal. 4. Pulmonary branches. 6. 

 Stomach. 6. Liver. 



