[Illustration: FIG. 35. These three figures illustrate perhaps more clearly the _action_ of the muscles indicated FIGS. 26-34. The arrows show the direction of the pull of the muscles. The result of this action is the new position of the cartilages and vocal bands, which is shown by red outlines. The muscle is also depicted in red. The heavier outer rim is to indicate the thyroid cartilage. By comparing the upper and the lowest figure it will be seen that they are opposites. Of course, in phonation the vocal bands are never so much separated as shown in the illustrations. Rather does the lower figure indicate a case of extreme separation due to a very deep inspiration. However, these illustrations are merely diagrams meant to indicate in a general way the manner of the working of parts. For exact pictures of the vocal bands and related parts, see Chapter VII.] CHAPTER VII. SOUND--THE LARYNGOSCOPE--THE LARYNX RECONSIDERED. Before discussing our subject further it is desirable that some attention be given to a few of the fundamental principles of that department of physics termed _acoustics_, and which deals with the subject of sound. If the student has the opportunity to study this subject theoretically and practically, as it is set forth in some good work on physics, he will have no reason to regret the time spent. A deep knowledge of the laws of sound is not absolutely essential, or even highly necessary, for a sufficient understanding of the principles involved in voice-production. It is, however, all-important that a few facts and principles be thoroughly grasped. For those who feel that they have the time for a study of acoustics, the author would especially recommend Tyndall's work on sound, in which the subject is treated with wonderful clearness and charm. What we endeavor now to bring before the reader we have found sufficient for nearly all the purposes of the voice-user.