nature which differ sufficiently from those encountered in later life to be of great interest and importance. The perfection of the technic of direct laryngoscopic examination has naturally removed the uncertainty which previously obscured the diagnosis and management of these disorders. It is the more surprising therefore to note the frequency with which this important procedure is still deferred or altogether omitted. It should be considered axiomatic that any stridor observed in infancy requires careful direct laryngoscopic examination regardless of other clinical findings which may apparently explain the disturbance. This contention is repeatedly emphasized in the study of 20 cases of chronic stridor in infancy on which this thesis is based.
EMBRYOLOGIC CONSIDERATIONSA brief resume of the more important phases of the development of the larynx is indispensable to an understanding of certain abnormalities encountered in infancy. It is an interesting clinical fact that despite the complicated formation true congenital malformations are exceedingly rare.The larynx, according to Frazer,1 is a compound formation consisting of an infraglottic portion, formed around the upper end of the tracheal tube, and a supraglottic portion, formed by a modification of the pharyngeal floor lying immediately around the sagittal, slitlike orifice of the pulmonary outgrowth (primitive glottis). The third, fourth and sixth branchial arches are intimately concerned with its development. By the fifth week of fetal life the two sixth arches have enlarged, forming on each side of the primitive glottis and behind the hypobranchial eminence two rounded masses identified as the arytenoid
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