EIGHTH PAIR. 559 



The Superior laryngeal is the nerve of sensation to the larynx. It is larger 

 than the preceding, and arises from the middle of the inferior ganglion of the 

 pneumogastric. It descends, by the side of the pharynx, behind the internal 

 carotid, where it divides into two branches, the external and internal laryngeal. 



The external laryngeal branch, the smaller, descends by the side of the 

 larynx, beneath the Sterno-thyroid, to supply the Crico-thyroid muscle and the 

 thyroid gland. It gives branches to the pharyngeal plexus, and the Inferior 

 constrictor, and communicates with the superior cardiac nerve, behind the common 

 carotid. 



The internal laryngeal branch descends to the opening in the thyro-hyoid 

 membrane, through which it passes with the superior laryngeal artery, and is 

 distributed to the mucous membrane of the larynx, and the Arytenoid muscle, 

 anastomosing with the recurrent laryngeal. 



The branches to the mucous membrane are distributed, some in front, to the 

 epiglottis, the base of the tongue, and epiglottidean gland ; and others pass back- 

 wards, in the aryteno-epiglottidean fold, to supply the mucous membrane sur- 

 rounding the superior orifice of the larynx, as well as the membrane which lines 

 the cavity of the larynx as low down as the vocal chord. 



The filament to the Arytenoid muscle is distributed partly to it, and partly to 

 the mucous lining of the larynx. 



The filament which joins with the recurrent laryngeal descends beneath the 

 mucous membrane on the posterior surface of the larynx, behind the lateral part 

 of the thyroid cartilage, where the two nerves become united. 



The Inferior or recurrent laryngeal, so called from its reflected course, is the 

 motor nerve of the larynx. It arises on the right side, in front of the subclavian 

 artery ; winds from before backwards round this vessel, and ascends obliquely to 

 the side of the trachea, behind the common carotid and inferior thyroid arteries. 

 On the left side, it arises in front of the arch of the aorta, and winds from before 

 backwards round the vessel at the point where the obliterated remains of the 

 ductus arteriosus are connected with it, and then ascends to the side of the trachea. 

 The nerves on both sides ascend in the groove between the trachea and oesophagus, 

 and, piercing the lower fibres of the Inferior constrictor muscle, enter the larynx 

 behind the articulation of the inferior cornu of the thyroid cartilage with the 

 cricoid, being distributed to all the muscles of the larynx, excepting the Crico- 

 thyroid, and joining with the superior laryngeal. 



The recurrent laryngeal, as it winds round the subclavian artery and aorta, 

 gives off several cardiac filaments, which unite with cardiac branches from the 

 pneumogastric and sympathetic. As it ascends the neck, it gives off cesophageal 

 branches, more numerous on the left than on the right side, which supply the 

 mucous membrane and muscular coat of the oesophagus ; tracheal branches to the 

 mucous membrane and muscular fibres of the trachea; and some pharyngeal 

 filaments to the Inferior constrictor of the pharynx. 



The Cervical cardiac branches, two or three in number, arise from the pneumo- 

 gastric, at the upper and lower part of the neck. 



The superior branches are small, and communicate with the cardiac branches 

 of the sympathetic, and with the great cardiac plexus. 



The inferior cardiac branches, one on each side, arise at the lower part of the 

 neck, just above the first rib. On the right side, this branch passes in front of 

 the arteria innominata, and anastomoses with the superior cardiac nerve. On the 

 left side, it passes in front of the arch of the aorta, and anastomoses either with 

 the superior cardiac nerve or with the cardiac plexus. 



The Thoracic cardiac branches, on the right side, arise from the trunk of the 

 pneumogastric, as it lies by the side of the trachea: passing inwards, they terminate 

 in the deep cardiac plexus. On the left side, they arise from the left recurrent 

 laryngeal nerve. 



The Anterior pulmonary branches, two or three in number, and of small size, 

 are distributed on the anterior aspect of the root of the lungs. They join with 

 filaments from the sympathetic, and form the anterior pulmonary plexus. 



