LARYNX, TRACHEA AND LUNGS 



l6 7 



FIG. 172. Entrance to 

 larynx in a 15 to 1 6 mm. human 

 embryo (from Kallius). X 15. 

 p, Pharyngo-epiglottic fold; e, 

 epiglottic fold ; I.e., lateral part 

 of epiglottis; cun., cuneiform 

 tubercle; corn., corniculate 

 tubercule. 



b.l. 



anlages of the larynx and trachea. The rounded end of the ridge is the 



unpaired anlage of the lungs. 



Externally, two lateral longitudinal grooves 



mark off the dorsal esophagus from the ventral 



respiratory anlages. The lung anlage rapidly 



increases in size, and becomes bilobed in em- 

 bryos of 4 to 5 mm. A fusion of the lateral 



furrows progressing cephalad, constricts first 



the lung anlages and then the trachea from the 



esophagus. At the same time the laryngeal 



portion of the groove and ridge advances 



cranially until it lies between the fourth 



branchial arches (Fig. 87). At 5 mm. the 



respiratory apparatus consists of the laryngeal 



groove and ridge, the tubular trachea, and the 



two lung buds (Fig. 711 D). 



The Larynx. In embryos of 5 to 6 mm. 



the oral 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. 157 B). The 

 transverse ridge becomes the 

 epiglottis, and, as we saw in con- 

 nection with the development of 

 the tongue, it is derived from the 

 third and fourth branchial arches. 

 In embryos of 15 mm. the ary- 

 tenoid swellings are bent near the 

 middle. Their caudal portions 

 become parallel, while their ceph- 

 alic portions diverge nearly at 

 right angles (Fig. 172). The glottis, 

 opening into the larynx, thus be- 

 comes T-shaped and ends blindly, 

 as the laryngeal epithelium has 

 fused. In 40 mm. (CR) fetuses 

 this fusion is dissolved, the ary- 

 tenoid swellings are withdrawn 

 from contact with the epiglottis, 

 and the entrance to the larynx 

 becomes oval in form (Fig. 173). 



At 27 mm. the ventricles of the larynx appear, and, at 37 mm. (CR), 



their margins indicate the position of the vocal cords. The elastic and 



muscle fibers of the cords are developed by the fifth month. 



pl.pt>.* - 



f.i.a _. 



FIG. 173. The larynx of 160 to 230 mm. 

 human fetus (Soulie and Bardier). X 6. b.l.., 

 Base of tongue; e., epiglottis; f.i.a., interary- 

 tenoid fissure; o.l., orifice of larynx ; pl.a.e., plica 

 ary-epiglottica; pl.ph.e., plica pharyngo- 

 epiglottica: cun., cuneiform tubercle; corn., 

 corniculate tubercle. 



