THE LARYNX. 



189 



are numerous and relatively large over the false vocal cords (plica ventricu- 

 lares} and plentiful in the ventricles. They do not occur on the upper 

 surface of the true vocal cords within 3-4 mm. of their free margins, but 

 beneath the latter the glands form almost a continuous layer. 



The vocal folds, less appropriately called the vocal cords, are two 

 duplicatures of mucous membrane which cover the free median margins of 

 the lateral crico-thyroid membranes. This part of the membrane, often 

 designated the thyro-arytenoid ligament, is attached to the thyroid cartilage 

 in front and to the vocal process of the mobile arytenoid cartilage behind, 



muscle 

 Submucous layer 



Epithelium of 

 oesophagus 



Circular muscle 



Muscle 



Mucous 

 membrane 



Trachea 

 Glands 



Cartilage 



FIG. 235. Transverse section of trachea and oesophagus of child. X 15. 



and is directly influenced by the contractions of the thyro-arytenoid muscle, 

 which lies against the membrane externally and inserts many of its fibres 

 directly into the fibrous band. The submucous tissue being wanting over 

 the vocal cord, the here thin mucous membrane is intimately attached to the 

 underlying fibrous stratum of the thyro-arytenoid ligament, thus insuring 

 accurate response to the changes induced by muscular action. Small masses 

 of elastic cartilage, from 2-3 mm. long, are occasionally found in the anterior 

 ends of the vocal cords; smaller pieces of similar tissue are quite common 

 in the ventricular plicae. 



The numerous blood-vessels supplying the larynx are distributed 

 chiefly to the mucous membrane, in which the main capillary network lies 

 close beneath the epithelium. Other branches are given off within the sub- 

 mucous layer and provide the capillary supply for the numerous glands. 

 The lymphatics are well represented throughout the greater part of the 

 laryngeal mucous membrane, especially in the region of the ventricle and 

 false vocal folds. Over the true cords, however, they are very feebly devel- 

 oped, but below them the lymphatics are again numerous. Where abundant, 

 the lymph-channels are present within the mucosa as a superficial and a deeper 

 network, which communicate and pass to the cervical lymph-nodes. 



