466 



HISTOLOGY 



utriculus. Since at one of their ends the superior and posterior ducts unite 

 in a single stalk before entering the utriculus, there are but five openings 

 for the three ducts (Fig 472, D). Near one end of each duct there is a 

 dilatation or ampulla, where nerves terminate. 





X 9. 



PIG. 471. SECTIONS OF RABBIT EMBRYOS TO SHOW THE DEVELOPMENT OF THE EAR. 

 , 9 days >4 3.8 mm.; B, 10 days, 3-4 mm-.; C, 12$ days, 7.5 mm.; D, 14 days, 10 mm. a.,7Ectoderma 

 epithelium which forms the membranous internal ear; a. has., basilar artery; ch. t., chorda tympani ; 

 d. c., cochlear duct; d. e., endolymphatic duct; d. s. 1., lateral semicircular duct; d. s. s., superior semi- 

 circular duct; ep., epidermis-, fa., facia! nerve; meten., metencephalon; 



pharynx. 



m. t. , medullary- tube; ph., 



D 



FIG. 472. LATERAL OR EXTERNAL SURFACES OF MODELS OF THE MEMBRANOUS PORTION OF THE LEFT 



INTERNAL EAR FROM HUMAN EMBRYOS. Different enlargements. (After His, Jr.) 

 A, from an embryo of 6.9 mm.; B, 10.2 mm.; C, 13.5 mm.; and D, 22 mm. am., ampulla; c v., caecum 



vestibulare of d. c., cochlear duct; d. e., endolymphatic duct; d. s. 1., d. s. p., and d. s. s.. lateral, 



posterior, and superior semicircular ducts; sac., sacculus; ut., utriculus. 



While the formation of the semicircular ducts is occurring in the upper 

 part of the auditory vesicle, the lower portion elongates and its end be- 

 comes coiled, eventually making two and a half revolutions. The coiled 



