FIG. 592. SEMIDIAGRAMMATIC ILLUSTRATIONS OF SUCCESSIVE STAGES IN THE DE- 

 VELOPMENT OF THE INTERNAL EAR OF THE CHICK. 



A, 45 hour embryo; B, 60 hour embryo; C, 5 day embryo; D, 7 day embryo; M, 

 wall of neural canal at level of metencephalon ; E, epidermal ectoderm; op, otic pit; 

 oc, otocyst (otic vesicle); DE, ductus endolymphaticus; SE, saccus endolymphaticus; 

 cd, cochlear duct; u, utriculus; dss, superior semicircular duct; dsl, lateral semi- 

 circular duct. 



c? 



FIG. 593. WAX RECONSTRUCTIONS OF THREE EARLY STAGES IN THE DEVELOP- 

 MENT OF THE INTERNAL EAR (MEMBRANOUS LABYRINTH) OF MAN. 



A, lateral view, from a 6.6 mm. embryo; B, lateral view from an 11 mm. embryo; 

 C, front view from a 20 mm. embryo (these correspond approximately to stages 

 B, C, and D of the preceding figure). DE, ductus endolymphaticus; SE, saccus 

 endolymphaticus; VP, vestibular pouch; cp, cochlear pouch; ap, absorption focus; 

 c, crus; s, sacculus; u, utriculus; cd, cochlear duct; dss, dsp, and dsl, superior, pos- 

 terior, and lateral semicircular ducts. (After Streeter.) 



718 



