ANATOMY AND PHYSIOLOGY OF THE CHILD'S LARYNX The two plates of the thyroid cartilage are not united at such a sharp angle as in the adult, and their section fornis an almost semicircular arch. The line of union in the middle can hardly be felt. A further difference is the tendency for the cricoid plate to incline posteriorly. This is niost marked in the newborn infant, and disappears about the fourth year. The nicking of the laryngotracheal tube during the first year of life is explained by this anatomical fact. The glottis of the nursing infant is proportionately much smaller than in the adult, but this peculiarity of the child's larynx gradually disappears as further development takes place. It is believed that the larynx does not develop much between the fifth or sixth years and the age of puberty. After this period is reached however, the larynx grows rapidly. In the male, there is a change in the shape of the thyroid plates, and the laryngeal promi nences arc formed. Figs, 93 and 91 represent the relation between the fcetal and the adult larynx (vertical sections).
In Fip. 93 and 94, the nicking of the laryngotracheal tube, and the separation of the thyroid cartilage from the cricoid cartilage, which, in relation to the glottis, is much greater than in the adult, is clearly represented. The thyrohyoid region is worthy of note. The hyoid bone rests on the upper edge of the thyroid cartilage, For this reason, the thyrohyoid space is much lower than in the adult. A dis tinct median and lateral thyrohyoid ligament, only appears in the seventh year.
The physiology of the child's larynx has been only slightly inves tigated. The physiological relations of the movements of the separate laryngeal cartilages to each other have not been studied at all. The peculiarities of the child's larynx are associated Milt it's anatomy, and the changes which develop as the child grows older, play an impor tant role in voice production. This however has no important bearing upon the pathology of the child's larynx.