THE LARYNX. 



1827 



Fig. 1556. 



thyroid branch meets its fellow so as to form an arch across the median line and 

 sends perforating branches into the larynx through the crico-thyroid membrane. 

 The inferior laryngeal from the inferior thyroid reaches the region of the back of the 

 larynx from the side. It anastomoses with the superior laryngeal and sometimes 

 sends branches through or into the arytenoid muscle. The vocal cords possess 

 relatively few blood-vessels. 



The veins correspond in the main to the arteries, but, owing to their greater 

 size and freer anastomoses, they seem in more immediate relation with those of the 

 thyroid body. Moreover, they tend to form a median descending vessel in the front 

 of the neck. There is a plexus on the pharyngeal side of the back of the larynx 

 which communicates through the folds at the sides of the entrance with the veins of 

 the dorsum of the tongue. The inferior laryngeal vein empties into the inferior 

 thyroid through a circular plexus around the entrance of the trachea. 



The lymphatics of each side empty into two chief vessels, of which the superior 

 pierces the thyro-hyoid membrane, carrying the lymph from the supraglottic region 

 to the nodes under or near the sterno-mastoid. The inferior vessel descends under 

 the mucous membrane outward and backward to the nodes along the posterior sur- 

 face of the trachea. It may, however, open into an inconstant node in front of the 

 crico-thyroid membrane. This node occurs in 44 per cent. 

 of adults and in 57 per cent, of children. It may be 

 double. ^ 



Nerves. — These are the superior and the inferior 

 laryngeal nerves, both from the vagus. The superior, on 

 reaching the thyro-hyoid membrane, divides into an exter- 

 nal and an internal branch. The external continues down- 

 ward and forward to the crico-thyroid muscle, which it 

 supplies. It is in relation with the pharyngeal plexus and 

 the superior sympathetic ganglion. The internal branch 

 pierces the membrane together with the superior laryngeal 

 artery, and supplies the greater part of the mucous mem- 

 brane. Its ramifications are in two groups : ascending 

 ones to the epiglottis, the region just before it, and to the 

 aryepiglottic folds ; others passing to the mucous mem- 

 brane within the larynx and to that of the posterior surface 

 looking towards the pharynx. The inferior laryngeal, as- 

 cending by the side of the back of the trachea, divides into 

 two branches. The branch nearer the median line inner- 

 vates the posterior crico-arytenoid and the arytenoid mus- 

 cles. Its fibres, in part sensory, enter into communication 

 with those of the superior laryngeal. The other branch 

 of the inferior laryngeal goes to the other intrinsic muscles 

 of the larynx. Thus the superior laryngeal divides into 

 a motor branch that ends in one muscle, and a sensory division which plays the 

 greater part in supplying the mucous membrane. The inferior laryngeal is also a 

 mixed nerve, but chiefly motor. It supplies all the other muscles and helps to sup- 

 ply the mucous membrane. A remarkable peculiarity of the sensory nerves is a 

 tendency to cross the median line, so that certain regions are reached from both 

 sides. 



The general teaching by English anatomists has been that the superior laryngeal 

 is as above stated and that the inferior is purely motor. Exner^ made observations, 

 in part confirmed and in part disputed, to the effect that both nerves are mixed, 

 supplying both muscles and mucous membrane (the superior supplying, in part at 

 least, certain muscles within the larynx), and that both motor and sensory fibres 

 cross the median line, so that some muscles receive the corresponding nerve of both 

 sides. Moreover, he found in some animals a middle laryngeal nerve from the 

 pharyngeal branch of the vagus, of which the analogue exists in man, in whom it 

 goes, together with the superior laryngeal, to the crico-thyroid muscle of both sides. 



^ Nicolas in Poirier's Traitd d'Anatomie Humaine. 

 ^ Vienna Akad. Sitzungsbericht, 1884. 



Vestibule 



False vocal 

 cord 



Ventricle 



A'ocal cord 



.Trachea 



Cast of cavity of larynx and 

 adjacent part of trachea ; anterior 

 aspect. 



