Ill 



PROBATION AND AETICULATION 



133 



produced by membranous tongues, but its formation is easier 

 in proportion as the slit is narrower. The extra tubes which 

 form the body of these instruments have a great influence on pitch 

 and timbre ; the tones become deeper as the body is longer, but 

 never drop an octave as is the case in instruments with rigid lips. 



As a musical instrument the larynx has many points of 

 resemblance with tongued instruments. The formation of laryn- 

 geal sounds depends on the passage of air through a slit (opening 

 of the glottis) which is rhythmically altered in width by the 

 vibration of membranous tongues (the vocal cords) so as to break 

 up the air blast that passes through it. The wind-pipe is formed 

 by the bronchi and trachae, 

 as in brass instruments ; the 

 sounding -pipe or resonator 

 by the cavities lying above 

 the glottis, i.e. the larynx and 

 pharynx, the mouth and the 

 nose. On the other hand 

 the vocal apparatus is dis- 

 tinguished from all tongued 

 musical instruments by the 

 fact that the vocal cords 

 which represent the tongues 

 can change at any moment 

 in length, breadth, diameter, 

 and tension, even independ- 

 ently of the pressure of the 

 air blast which throws them 

 into vibration. 



A clear idea of the con- 

 struction of the larynx is 

 essential in order to understand the complex mechanism of 

 phonation. 



II. The larynx consists of a cartilaginous skeleton which is only 

 partially ossified. The laryngeal cartilages are united by fibrous 

 membranes, ligaments, small articular capsules, and by a series of 

 small muscles, which constrict or dilate the glottis, stretch or relax 

 the vocal cords, and regulate the thickness of their vibrating 

 portions. 



The cricoid cartilage is shaped like a signet ring with its narrow 

 part forward, and its face backward. Its lateral surface articulates 

 with the inferior cornua of the thyroid cartilage. The two 

 cartilages can rotate round the horizontal axis of these articular 

 surfaces, the anterior surface of the thyroid may be displaced 

 forwards and downwards, or the front part of the cricoid cartilage 

 may be pushed up towards the thyroid. The triangular bases of 

 the two arytenoid cartilages articulate at the upper margin of the 



K i 



cr 



FIG. 87. Laryngeal cartilages, seen from behind. 

 (Henle.) t, thyroid cartilage ; Cs, Ci, its superior 

 and inferior horns ; Pm, Pv, processus mtisculus 

 and vocalis of arytenoid cartilage ; co, cartilage 

 of Santorini ; w, cricoid cartilage. 



