838 PHYSIOLOGY. 



In the thorax the vagus gives off cardiac and pulmonary 

 branches. These also anastomose with the sympathetics to form 

 numerous plexuses. 



The terminal branches of the vagus are distributed to the stom- 

 ach, solar plexus, and also to the hepatic plexus of the sympathetic. 



The most striking feature with regard to the vagus is the great 

 number of its anastomoses. It is a very complex nerve and in no 

 part of its course is it exclusively itself. 



Physiology. The relationship existing between the vagus and 

 spinal accessory nerves is a very intimate one by reason of their 

 anastomoses. This makes the determination of the true nature of 

 the vagus one of the difficult problems of physiology. 



It is certain that the vagus is endowed with sensibility, for the 

 suppression of the spinal accessory does not deprive the parts of any 

 sensibility in any portion of their common distribution. But, as the 

 spinal accessory is motor and the vagus sensory, it does not neces- 

 sarily follow that the latter nerve is exclusively sensory and that all 

 movements realized by association should be the special work of the 

 spinal accessory. It was Bernard who first demonstrated that the 

 vagus in itself is a mixed nerve. After he had torn out all of the 

 root-fibers of the spinal accessory in animals he found that the motor 

 acts of the larynx persisted in the phenomena of respiration. How- 

 ever, while the vagus in itself is a mixed nerve and has a certain 

 amount of motor functions, yet its principal role is of a sensory 

 nature. 



The mode of distribution of the vagus indicates that the nerve 

 exercises some action upon (1) the digestive apparatus, (2) upon the 

 respiratory apparatus, (3) upon the circulation, (4) upon the hepatic 

 apparatus, and (5) an indirect action upon the kidneys and supra- 

 renal glands. 



Pathology. The recurrent is more liable to be pressed upon by 

 reason of its peculiar course and its direct relations with the great 

 vessels and body of the thyroid. As the vagus is a mixed nerve, it 

 is very evident that compression causes troubles in motion and sensi- 

 bility, either isolated or conjointly. 



Any lesions located at the origin of the vagus cause phenomena 

 of irritation in the whole sphere of distribution of this nerve. Ee- 

 flexly the vagus is capable of affecting the chorda tympani and 

 increasing the flow of saliva. It is for this reason that intestinal 

 parasites often cause ptyalism. 



The sensibility of the branches of the vagus in the stomach 



