174 



THE ENTODERMAL CANAL AND ITS DERIVATIVES 



apparatus consists of the laryngeal groove and ridge, the tubular trachea and the 

 two lung buds. 



The Larynx. In embryos of 5 to 6 mm. the oval end of the laryngeal groove 

 is bounded on either side by two rounded prominences, the arytenoid swellings 

 which, continuous orally with a transverse ridge, form the furcula of His (Fig. 

 152 B). The transverse ridge becomes the epiglottis and, as we saw in connec- 

 tion with the development of the tongue, it is derived from the third and 

 fourth branchial arches. In embryos of 15 mm. the arytenoid swellings are 

 bent near the middle toward the 

 median line. Their caudal portions 

 become parallel, while their cephalic 

 portions diverge nearly at right angles 

 (Fig. 1 66). The opening into the 

 larynx thus becomes T-shaped and 



r.ph.e.... 



T 



-* r.a.e. 



ett. 



FIG. 166. Entrance to larynx in a forty- to 

 forty-two-day human embryo (from Kallius): 

 t, tuberculum impar; p, pharyngo-epiglottic 

 fold; e, epiglottic fold; l.e, lateral part of epi- 

 glottis; cu, cuneiform tubercle; corn, cornicular 

 tubercle. 



FIG. 167. The larynx of 16 to 23 cm. human 

 embryos (Soulie and Bardier). From a dissection. 

 b.l., base of tongue; e, epiglottis; f.i.a., interary- 

 tenoid fissure; r.a.e., plica ary-epiglottica; r.ph.e., 

 plica pharyngo-epiglottica; o.L, orifice of larynx; 

 i.e., tuberculum cuneiformis; t.S., tuberculum corni- 

 culatum. 



ends blindly, as the laryngeal epithelium has fused. In 40 mm. embryos this 

 fusion is dissolved, the arytenoid swellings are withdrawn from contact with 

 the epiglottis and the entrance to the larynx becomes oval in form (Fig. 167). 

 At 27 mm. the ventricles of the larynx appear and at 37 mm. their margins 

 indicate the position of the vocal cords. The epithelium of the vocal cords 

 is without cilia. The elastic and muscle fibers of the cords are developed by 

 the fifth month. 



At the eighth week the cartilaginous skeleton of the larynx is indicated by a surrounding 

 condensation of mesenchyme. The cartilage of the epiglottis appears relatively late. The 



