732 VOICE AND SPEECH. [CH. Liv. 



the base of the tongue. The necessary closure of the glottis during swallow- 

 ing is brought about by the contraction of the arytenoid and thyro-arytenoid 

 muscles ; by this means the arytenoid cartilages are drawn towards each 

 other, and also forwards into contact with the posterior surface of the 

 epiglottis (Anderson Stuart). Henle remarks that "the muscles which lie 

 in the space enclosed by the lamina? of the thyroid cartilage and above the 

 cricoid may be regarded in their totality as a kind of sphincter such as 

 is found in its simplest form embracing the entrance of the larynx in 

 reptiles " (Quain's Anatomy). 



Nerves. The larynx is supplied by two branches of the vagus ; the 



Fig. 55 $. The parts of the Laryngoscope. 



superior laryngeal is the sensory nerve ; by its external branch, it supplies 

 one muscle, namely, the crico-thyroid. These fibres, however, probably 

 arise from glosso-pharyngeal rootlets (see p. 629). The rest of the muscles 

 are supplied by the inferior laryngeal nerve, the fibres of which come from 

 the spinal accessory, not the vagus proper. 



The laryngoscope is an instrument employed in investigating during 

 life the condition of the pharynx, larynx, and trachea. It consists of a large 

 concave mirror with perforated centre, and of a smaller mirror fixed in a 

 long handle. It is thus used : the patient is placed in a chair, a good light 

 (argand burner, or electric lamp) is arranged ou one side of. and a little above 

 his head. The operator fixes the large mirror round his head in such a manner, 

 that he looks through the central aperture with one eye. He then -<>nt- 

 himself opposite the patient, and so alters the position of the mirror, which 



