VOICE pe-~ an inch, from before backwards, and from 6 to 12 millimetres across its widest part, according to the degree of dilatation. In females and in males before puberty the antero - posterior diameter is about 17 millimetres and its transverse diameter about 4 millimetres. The vocal cords of the adult male are in length about 15 millimetres, and of the adult female about 11 milli metres. The larynx is lined with a layer of epithelium, which is closely adherent to underlying structures, more especially over the true vocal cords. The cells of the epithe- r Hum, in the greater portion of FIG. 4.-Laryngoscopic view of the glottis. t! 10 lnr v nf tl, 1,,,,o,. l > *. n S" e ; /, epiglottis ; P e, pharyngo- epiglottic fold; g, pharyngo-laryngeal groove ; ae, aryteno-epiglottic fold ; c, cuneiform cartilage, or cartilage of Wrisberg ; ar, arytenoid cartilage ; r, intcr-arytenoid fold ; o, glottis ; v, ven tricle ; ti, inferior or true vocal cord ; ti is, superior or false vocal cord. (From Mandl.) the larynx, are of the columnar ciliated variety, and by the vi bratory action of the cilia mucus is driven upwards, but over the true vocal cords the epithelium is sqnamous. Patches of squa- mous epithelium arc also found in the ciliated tract above the glottis, on the under surface of the epiglottis, on the inner surface of the arytenoid cartilages, and on the free border of the upper or false cords. Numerous mucous glands exist in the lining membrane of the larynx, more especially in the epiglottis. In each laryngeal pouch there are sixty to seventy such glands, surrounded by fat. "We are now in a position to understand the action of the muscles of the larynx by which the vocal cords, forming the rima glottidis, can be tightened or relaxed, and by which they can be approximated or i separated. Besides certain extrinsic muscles sterno-hyoid, omo-hyoid, sterno - thyroid, and thyro-hyoid 16 which move the larynx as a whole, there are intrinsic muscles which move the cartilages on each other. Some of these are seen in fig. 5. These muscles are (a) the crico-thy- 14-) roid, (b) the posterior crico-arytenoid, (c) the lateral crico-arytenoid, (d) the thyro - arytenoid, (e) the aryten oid, and (/) the aryteno-epiglot- tidean. Their actions will be readily understood with the aid of the dia grams in fig. 6. (1) The crico-thyroid is a short thick triangular muscle, its fibres passing from the cricoid FIG. 5. Muscles of the left side of cartilage obliquely upwards and out- the laryilx > seen from within * wo wards to be inserted into the lower border of the thyroid cartilage and to the outer border of its lower horn. When the muscle contracts, the cri coid and thyroid cartilages are ap proximated. In this action, how ever, it is not the thyroid that is thirds natural size. 1, hyo-epi- glottic ligament, seen in profile ; 2, epiglottis; 3, aryteno-epiglot tic muscle ; 4, Santorini s car tilage ; 5, oblique arytenoid muscle ; 6, transverse arytenoid muscle, seen in profile ; 7, pos terior crico-arytenoid ; 8, lateral crico-arytenoid ; 9, lower cornu through ; 12, long thyro-epiglottic muscle (a variety); 13, inferior thyro - ary tenoid : 14, thyro-epi glottic ; 15, superior thyro-ary- tenoid ; 16, median thyro-hyoid ligament. (From Krause.) of thyroid cartilage cut through ; depressed on the cricoid, as is gener- 10 , insertion of posterior portion ally stated, but, the thyroid being of crico-thyroid muscle ; 11, left fixed in position by the action of the lamina of thyroid cartilage cut extrinsic muscles, the anterior border of the cricoid is drawn upwards, whilst its posterior border, in con sequence of a revolution around the axis uniting the articulations be tween the lower cornua of the cricoid and the thyroid, is de pressed, carrying the arytenoid cartilages along with it. Thus the vocal cords are stretched. (2) The thyro-arytcnoid has been divided by anatomists into two parts one, the internal, lying close to the true vocal cord, and the other, external, immediately within the ala of the thyroid cartilage. Many of the fibres of the anterior portion pass from the thyroid cartilage with a slight curve (concavity inwards) to the processus vocalis at the base of the arytenoid cartilage. They are thns parallel with the true vocal cord, and when they contract the arytenoids are drawn forwards, carrying with them the posterior part of the cricoid and relaxing the vocal cords. Thus the thyro-arytenoids are the antagonists of the crico- thyroids. Ludwig has pointed out that certain fibres (portio -ary -vocalis} arise from the side of the cord itself and pass obliquely back to the processus vocalis. These will tighten the parts of the cord in front and relax the parts behind their points of attachment. Some of the fibres of the outer portion run obliquely upwards from the side of the crico-thyroid membrane, pass through the antero-posterior fibres of the inner portion of the muscle, and finally end in the tissue of the false cord. These fibres have been supposed to render the edge of the cord more prominent. Other fibres inserted into the processus vocalis will rotate slightly the arytenoid outwards, whilst a few passing up into the aryteno- epiglottidean folds may assist in depressing the epiglottis (Quain). FIG. 6. Diagrams explaining the action of the muscles of the larynx. The dotted lines show the positions taken by the cartilages and the true vocal cords by the action of the muscle, and the arrows show the general direction in which the muscular fibres act. A, Action of crico-thyroid : 1, cricoid cartilage ; 2, arytenoid cartilage ; 3, thyroid cartilage ; 4, true vocal cord ; 5, thyroid cartilage, new position ; 6, true vocal cord, new position. B, Action of arytenoid : 1, section of thyroid ; 2, arytenoid ; 3, posterior border of epiglottis ; 4, true vocal cord ; 5, direction of muscular fibres ; 6, arytenoid, new position ; 7, true vocal cord, new position. C, Action of lateral crico-arytenoid ; same description as for A and B ; 8, posterior border of epiglottis, new position ; 9, arytenoid in new position. D, Action of posterior crico-arytenoid ; same description. (From Bcaunis and Bouchard.) (3) The posterior and lateral crico-arytenoid muscles have antagon istic actions, and may be considered together. The posterior arise from the posterior surface of the cricoid cartilage, and passing up wards and outwards are attached to the outer angle of the base of the arytenoid. On the other hand, the lateral arise from the upper border of the cricoid as far back as the articular surface for the arytenoid, pass backwards and upwards, and are also in serted into the outer angle of the base of the arytenoid before the attachment of the posterior crico-arytenoid. Imagine the pyra midal form of the arytenoid cartilages. To the inner angle of the triangular base are attached, as already described, the true vocal cords ; and to the outer angle the two muscles in question. The posterior crico -arytenoids draw the outer angles backwards and in wards, thus rotating the inner angles, or processus vocalis, outwards, and, when the two muscles act, widening the rima glottidis. This action is opposed by the lateral crico-thyroids, which draw the outer angle forwards and outwards, rotate the inner angles inwards, and thus approximate the cords. (4) The arytenoids pass from the one arytenoid cartilage to the other, and in action these cartilages will be approximated and slightly depressed. (5) The aryteno-epi- glottidcan muscles arise near the outer angles of the arytenoid ; their fibres pass obliquely upwards, decussate, and are inserted partly into the outer and upper border of the opposite cartilage, partly into the aryteno-epiglottic fold, and partly join the fibres of the thyro- arytenoids. In action they assist in bringing the arytenoids to gether, whilst they also draw down the epiglottis, and constrict the upper aperture of the larynx. The vocal cords will be also relaxed by the elasticity of the parts. 2. General Physiological Characters. As already stated, the intensity or loudness of voice depends on the amplitude of the movement of the vocal cords. Pitch depends on the number of vibrations per second ; and the length, size, and degree of tension of the cords will determine the number of vibrations. The more tense the cords the higher the pitch, and the greater the length of the cords the lower will be the pitch. The range of the human voice is about three octaves, that is from fa x (87 vibrations per second) to so! 4 (768 vibrations). In men, by the development of the larynx, the cords become more elongated than in women, in the ratio of 3 to 2, so that the male voice is of lower pitch and is usually stronger. At the age of puberty
the larynx grows rapidly, and the voice of a boy " breaks "