1270 



HUMAN ANATOMY. 



more minute sympathetic ganglia and ramifies over the middle constrictor of the 

 pharynx. It suppUes motor fibres to the muscles of the pharynx and of the soft 

 palate, with the exception of the stylo-pharyngeus and the tensor palati. From the 

 plexus proceed sensory filaments to the mucous membrane of the pharynx. A 

 filament from this plexus, the lingual bj'aiich of the vagus (r. lingualis vagi), com- 

 posed of fibres from both the ninth and tenth nerves, joins the hypoglossal as it 

 hooks around the occipital artery. 



Variation. — A slender branch, the middle laryjtgeal nerve, is described as arising from the 

 pharyngeal plexus and supplying the crico-thyroid muscle, after which it pierces the crico- 

 thyroid membrane and supplies the mucous membrane of the lower part of the larjnx. 



4. The superior laryngeal nerve (n. laryngeus superior) (Fig. 1079) arises 

 from the middle of the ganglion of the trunk and takes a downward and inward 

 course beneath the external and internal carotid arteries toward the superior cornu 

 of the thyroid cartilage. It divides terminally into (a) the exteryial and (J)') iiiteryial 

 laryjigeal branches. 



Communications. — Before dividing, the superior laryngeal nei've receives filaments from 

 the superior cervical sympathetic cardiac and from the pharyngeal plexus. 



The cardiac twig given off by the extertial laryngeal nerve joins with the superior cervical 

 cardiac branch of the sympathetic. In the lower part of the larynx the external laryngeal nerve 

 inosculates with the terminal fibres of the internal laryngeal. 



At the inferior portion of the laryn.x, the ijilernal laryngeal nerve communicates with the 

 terminal filaments of the external laryngeal, and in this way supplies sensory fibres to the 

 mucous membrane lining the lower part of the larynx and to the muscles. 



Variation. — Instead of passing to the inner side of the internal carotid artery the nerve may 

 lie external to it. 



a. The external laryngeal branch (r. externus), much smaller than the in- 

 ternal, passes downward upon the inferior constrictor of the pharynx and beneath the 

 infrahyoid muscles to the crico-thyroid muscle, which it supplies. It sends filaments 

 also to the inferior pharyngeal constrictor and gives ofi a cardiac twig which joins the 

 superior cervical cardiac branch of the sympathetic. 



Variations. — The external laryngeal has been seen to send filaments to the thyroid gland, 

 the pharyngeal plexus, the sterno-hyoid, sterno-thyroid, thyro-hyoid and crico-arytenoideus lat- 

 eralis muscles and to the mucous membrane of the vocal cord and lower portion of the larynx. 



b. The internal laryngeal branch (r. internus), larger than the external, 

 passes downward and inward between the middle and inferior constrictors of the 

 pharynx and enters the larynx by piercing the thyro-hyoid membrane. By means 

 of its epiglottic, pharyngeal, descendiyig and communicating branches, it supplies the 

 mucous membrane covering the internal and pharyngeal surfaces of the larynx and 

 the mucous membrane of the base of the tongue. 



Variation.— Instead of piercing the thyro-hyoid membrane the nerve may obtain entrance 

 to the larynx through a small foramen in the thyroid cartilage. 



5. The superior cervical cardiac branch (rr. cardiaci superiores — both cervi- 

 cal cardiacs) arises from the vagus in the upper part of the neck. It either joins 

 a cardiac branch of the vagus or passes independently down the neck and along the 

 side of the trachea to end in the deep cardiac plexus (Fig. 1132). 



6. The inferior cervical cardiac branch leaves the vagus at the root of the 

 neck. On the right side it courses along the side of the innominate artery and either 

 independently, or after joining one of the other cardiac nerves, enters the deep car- 

 diac plexus. The left passes in front of the arch of the aorta and joins the superior 

 cervical cardiac branch of the left sympathetic to form the superficial cardiac plexus 

 (Fig. 1 132). 



7. The inferior or recurrent laryngeal nerve (n. recurrens) (Fig. 1080) 

 differs on the two sides in the early part of its course. The right nerve is given off at 



