THE VAGUS NERVE 99 



the inhibitory fibres and lead to a slowing of the heart-rate, 

 whereas vagal paralysis is followed by definite acceleration of 

 the rate, since the sympathetic fibres are no longer opposed. 



The recurrent (laryngeal) nerves arise at different levels on 

 the two sides of the body. The right recurrent nerve leaves 

 the vagus as it crosses the subclavian artery at the root of the 

 neck. It hooks round behind the termination of the innomin- 

 ate artery and then ascends in the groove between the oeso- 

 phagus and the trachea (Fig. 50), where it comes into close 

 contact with the lateral lobe of the thyreoid gland. 



The left recurrent nerve arises from the vagus as it crosses 

 the arch of the aorta in the thorax. It passes backwards 

 below the aortic arch and then upwards behind it. In the 

 first part of its course the left recurrent nerve lies a little 

 above the left bronchus and it may be compressed against 

 the aortic arch, when the bronchus is displaced upwards by 

 enlargement of the left atrium (auricle) of the heart in mitral 

 stenosis. It then ascends through the thorax in the groove 

 on the left side of the trachea (p. 339) and enters the neck, 

 where its relations are similar to those already described for 

 the recurrent nerve of the right side. 



The recurrent nerve supplies most of the intrinsic muscles 

 of the larynx, and its sensory fibres are distributed to the 

 laryngeal mucous membrane below the level of the vocal 

 folds (true vocal cords). 



Owing to its longer course, the left recurrent nerve is 

 subjected to pressure more often than the right. It may be 

 compressed (i) By aneurisms of the aortic arch (p. 319); 

 (2) by mediastinal tumours or enlarged mediastinal lymph 

 glands ; (3) by the left bronchus (vide supra]. The right 

 recurrent may be compressed near its origin by aneurism of 

 the terminal part of the innominate artery. Lastly, either or 

 both nerves may be affected in enlargements of the thyreoid 

 gland. 



The various results of paralysis of the recurrent nerves 

 are described on page 338. 



