An Introduction to Anatomy and Physiology (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: Creator. In front, it is formed by a cartilage, which from its resemblance to a shield is called thyroid; and this stands upon a circular one, the cricoid. Behind, two more are so formed and situated, as to leave only a small chink, the glottis, for the entrance of the air. The ary- tenoid cartilages being moveable, and furnished with ligaments (chordce vocales), and muscles, increase and diminish the size of the glottis, and thus modulate the voice. To prevent any thing from falling into the trachea in the act of deglutition, a little valve (epiglottis) is attached to the root of the tongue, to which the larynx ascends; when we swallow, and closes the glottis. Birds have two larynxes, one at the top, and the other at the bottom of the trachea; but no epiglottis. The inferior glottis corresponds to the reed of a hautboy or clarionet, and produces the tone or simple sound; while the superior larynx gives it utterance, as the holes of the instrument. The strength, and body of the note, depends on the extent and capacity of the trachea. The neighing of the horse, and the braying of the ass, are produced by a ligament, which crosses the larynx. As might be expected, fishes and insects have no organs of voice, and all the amphibia want the epiglottis. Respiration consists of two actions, inspiration and expiration. Atmospheric air, after being admitted into the lungs, returns charged with nearly ten per cent. of carbonic acid gas. Dr. Henry observes, that " when the state of the expired air is examined, a quantity of oxygen is found to have disappeared, equal to the volumeof the carbonic acid which has been formed. Now as carbonic acid has been proved to contain its own bulk of oxygen gas, it follows, that all the oxygen, which disappears in respiration, must have been expended in f...