576 NERVOUS SYSTEM. 



point of junction of the pneumogastric with the communicating branch 

 from the spinal accessory, so that probably the superior laryngeals 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 branch anastomoses with the inferior laryn- 

 geal 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 membrane 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 all sensory. This branch also supplies the crico-thyroid muscle. It 

 anastomoses with the inferior laryngeal nerve. An important branch, de- 

 scribed 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 sympathetic, 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 analagous fibres exist in man in the trunk of the pneumogastric. 



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

 rior 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 differences 

 in their anatomy upon the two sides. Upon 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 oesophagus. In its up- 

 ward course it gives off certain filaments which 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 filaments to the inferior constric- 

 tor of the pharynx and a branch which 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 of the in- 

 trinsic muscles of the larynx, except the crico-thyroids, which are supplied 

 by the superior laryngeal. Upon the right side the nerve winds from before 

 backward around the subclavian artery, and it has essentially the same course 

 and distribution as upon the left side, except that it is smaller and has fewer 

 filaments of distribution. 



The important physiological point connected with the anatomy of the re- 

 current laryngeals is that they animate all of the intrinsic muscles of the 

 larynx, except the crico-thyroid. Experiments have shown that these nerves 

 contain a large number of motor filaments derived from the spinal accessory 



