534 NERVOUS SYSTEM 



the ganglion of the trunk. Their filaments come from the side opposite 

 the point of junction of the pneumogastric with the communicating 

 branch from the spinal accessory, so that probably the superior laryn- 

 geals contain few if any motor fibres from the eleventh nerve. The 

 superior laryngeal gives off the external laryngeal, a long, delicate branch 

 which sends a few filaments to the inferior constrictor of the pharynx 

 and is distributed to the crico-thyroid muscle and the mucous membrane 

 of the ventricle of the larynx. The external laryngeal anastomoses with 

 the inferior laryngeal nerve and with the sympathetic. The internal 

 branch is distributed to the mucous membrane of the epiglottis, the 

 base of the tongue, the aryteno-epiglottidean fold and the mucous mem- 

 brane of the larynx as far down as the true vocal chords. A branch 

 from this nerve, in its course to the larynx, penetrates the arytenoid 

 muscle, to which it sends a few filaments, but these are sensory. This 

 branch also supplies the crico-thyroid muscle. It anastomoses with the 

 inferior laryngeal nerve. An important branch, described by Cyon and 

 Ludwig, in the rabbit, under the name of the depressor nerve, arises by 

 two roots, one from the superior laryngeal and the other from the trunk 

 of the pneumogastric. It passes down the neck by the side of the sym- 

 pathetic, and in the chest it joins filaments from the thoracic sympathetic, 

 to pass to the heart, between the aorta and the pulmonary artery. This 

 nerve is not isolated in the human subject, but it is probable that analo- 

 gous fibres exist in man in the trunk of the pneumogastric. 



It is important from a physiological point of view to note that the 

 superior laryngeal nerve is the nerve of sensibility of the upper part of 

 the larynx as well as of the supralaryngeal mucous membranes, and 

 that it animates a single muscle of the larynx (the crico-thyroid) and the 

 inferior constrictor of the pharynx. 



The inferior, or recurrent laryngeal nerves present some slight dif- 

 ferences in their anatomy on the two sides. On the left side the nerve 

 is the larger and is given off at the arch of the aorta. Passing beneath 

 this vessel, it ascends in the groove between the trachea and the oesoph- 

 agus. In its upward course it gives off filaments that join the cardiac 

 branches, filaments to the muscular tissue and mucous membrane of the 

 upper part of the oesophagus, filaments to the mucous membrane and 

 the intercartilaginous muscular tissue of the trachea, one or two fila- 

 ments to the inferior constrictor of the pharynx and a branch that joins 

 the superior laryngeal. Its terminal branches penetrate the larynx 

 behind the posterior articulation of the thyroid with the cricoid cartilage 

 and are distributed to all the intrinsic muscles of the larynx, except the 

 crico-thyroids, which latter are supplied by the superior laryngeal. On 

 the right side the nerve winds from before backward around the sub- 



