THE VAGUS NERVE 957 



(a) The internal branch accompanies the superior laryngeal arterj^ to the interval between 

 the upper border of the thyreoid cartilage and the great cornu of the hyoid bone. It passes 

 under cover of the thyreo-hyoid muscle and pierces the hyo-thyreoid mernbrane to gain the 

 interior of the pharynx, where it lies in the lateral wall of the sinus piriformis and divides into 

 a number of diverging branches. The ascending branches supply the mucous membrane on 

 both surfaces of the epiglottis, and probably that of a small part of the root of the tongue. The 

 descending branches ramify in the mucous membrane lining the larynx, and supply the mucous 

 membrane which covers the back of the cricoid cartilage. One of the descending branches 

 passes downward on the internal muscles of the larynx to anastomose with the terminal part of 

 the inferior (recurrent) laryngeal nerve. 



(b) The external branch runs downward on the inferior constrictor to the lower border of 

 the thyreoid cartilage, where it ends, for the most part, in the crico-thyreoid muscle. A few 

 filameiats pierce the crico-thyreoid membrane and are distributed to the membrane lining the 

 larynx. It occasionally gives off a cardiac branch which joins one of the cardiac branches of 

 the sympathetic; it also furnishes twigs to the inferior constrictor, and communicating twigs 

 to the pharyngeal plexus, and it receives a communication from the superior cervical ganghon 

 of the sympathetic. 



(5) The recurrent (inferior or recurrent laryngeal) nerve of the right side 

 arises from the vagus at the root of the neck in front of the right subclavian 

 artery. It hooks around the artery, passing below and then behind that vessel, 

 and runs upward and slightly medialward, crossing obliquely behind the common 

 carotid artery (fig. 744). Having gained the side of the trachea, it runs upward in 

 the groove between the trachea and the oesophagus, accompanying branches of the 

 inferior thyreoid artery, and, near the level of the lower border of the cricoid car- 

 tilage, becomes the inferior laryngeal nerve. 



In its course the right recurrent nerve gives off branches to the trachea, oesophageal branches 

 to the oesophagus and pharynx, and, near its commencement, one or more inferior cardiac 

 branches. It commtmicates with the inferior cervical sympathetic ganglion and with the superior 

 laryngeal nerve. 



The inferior laryngeal nerve, the continuation of the recurrent, ascends between the trachea 

 and oesophagus, enters the larynx under cover of the inferior constrictor of the pharynx, and 

 divides into two branches, anterior and posterior. The anterior branch passes upward and for- 

 ward on the crico-arytsenoideus lateralis and thyreo-arytsenoideus, and supphes these muscles 

 and also the vocalisj arytsenoideus obliquus, ary-epiglotticus, and thyreo-epiglotticus. The 

 posterior branch, passing upward, supphes the crico-arytaenoideus posterior and arytsenoideus 

 obUquus, and anastomoses with the medial branch of the superior laryngeal nerve. 



On the left side the recurrent nerve arises in front of the aortic arch and winds 

 around the concavity of the arch lateral to the ligamentum arteriosum. It crosses 

 obliquely behind the root of the left common carotid artery, gains the angular 

 interval between the cesophagus and trachea, and corresponds with the nerve of 

 the right side in the remainder of its course and distribution (fig. 744). 



(6) Cardiac branches. — Of these branches of the vagus, there are two sets, the 

 superior and inferior. All the branches of both sets pass to the deep part of the 

 cardiac plexus except a superior branch on the left side that passes to the super- 

 ficial part of the cardiac plexus. All contain visceral motor, sympathetic and 

 sensory fibres. 



(a) The superior (superior and inferior cervical) cardiac nerves arise from the vagus and 

 its branches in the neck (figs. 744, 786). Some of these branches on both sides join with the 

 cardiac branches of the sympathetic in the neck and pass with them to the cardiac plexus. Some 

 on the right side pass independently through the thorax to the deep part of the cardiac plexus, 

 and a branch on the left side passes through the thorax to the superficial part of the cardiac 

 plexus. 



(b) The inferior (thoracic) cardiac branches. — These branches on the right side arise in 

 part from the recurrent nerve and in part from the main trunk of the vagus, while on the left 

 side they usually arise entirely from the recurrent. All these branches pass to the deep part 

 of the cardiac plexus (figs. 744, 786). 



(7) The bronchial (pulmonary) branches are anterior and posterior (fig. 744) . 



(a) The anterior bronchial (pulmonary) branches consist of a few small branches which arise 

 at the upper border of the root of the lung. They pass forward to gain the anterior aspect of 

 the bronchus, where they communicate with the sympathetic and form the anterior pulmonary 

 plexus, from which fine twigs pass along the bronchus. 



(b) The posterior bronchial (pulmonary) branches. — Almost the entire remaining trunk 

 of the vagus usually divides into these branches, which join with branches from the second, 

 third, and fourth thoracic ganglia of the sympathetic to form the posterior pulmonary plexus 

 (fig. 744). The plexuses of the two sides join freely behind the bifurcation of the trachea, 

 and branches from the plexus pass along each bronchus into the lung. 



(8) The pericardial branches pass from the trunk of the vagus or from the bronchial or 

 oesophageal plexuses tothe anterior and posterior surfaces of the pericardium. They are 

 chiefly sensory. 



