With certain qualifications, it may be said that the action of the vocal bands is alike for all voices. In all cases a certain degree of approximation of the vocal bands is absolutely necessary for phonation, and the mechanism is generally similar in males and females till the highest tones, above alluded to, are reached. This is in harmony with the following facts: (1) The crico-thyroids are the muscles most in use in ordinary speech and in singing the lower tones. (2) Several muscles combine in relaxing and shortening the vocal bands. (3) The peculiar mechanism of the highest tones in a soprano voice of great compass is only to be explained by a combined action of several muscles, and a very delicate and precise use of the internal thyro-arytenoids attached along the whole length of the outer surface of the vocal bands. The larynx of the male differs from that of the female chiefly in its greater size, weight, etc. The vocal bands in the male may measure from three-fifths to four-fifths of an inch when relaxed, and from four-fifths to one inch when tense; in the female, from two-fifths to three-fifths of an inch when relaxed, and from three-fifths to four-fifths of an inch when tense. There are structural differences corresponding to and determining the kind of voice, as to range and power more especially. The bass singer has, as a rule, the largest larynx and the longest and heaviest vocal bands. At puberty the changes that take place in the body generally are associated with corresponding alterations in the larynx. The larynx grows, changes its proportions, etc., often somewhat rapidly, and the result may be a corresponding alteration in voice, as regards range, power, and quality. The voice, because of imperfect anatomical and physiological adjustment, may "break," to a greater or less extent. The same may take place, owing to similar imperfect adjustment, in old age, and temporarily, owing to disease, weakness, nervousness, fatigue, faulty production, etc. These facts indicate that under such circumstances the voice should be used with great care, not at all, or in a whisper, when the vocal bands are practically not in action. [Illustration: FIG. 45. Represents what the author has frequently seen, by the use of the laryngoscope, when a soprano is producing a very high head-tone, say C, D, or E in alt. It will be observed that the vocal bands approximate in front and behind ("stopped"), so that the only parts of the bands capable of vibration are those short portions which form the margins of the oval opening shown in the illustration. Only a very limited number of singers are capable of the delicate adjustments required.] In a singer highly endowed by nature and perfected by long training based on the soundest principles, the action of the muscles of the larynx may reach a degree of perfection only to be compared with that of the eye and ear.