median _ (section Aa.) 
ye 
/ 
ant. post. 
— ant. 
surface 
Ab. 
utr 
d.endolymph. / 
\ / 
\ / 
\ / 
/ 
absorption focus 
NX 
NEN 
Noo 
\ 
\ NS 
Cpe: 82s ENS SS i eD fe Steen ee ee 
\ 
Ba. 
crus comm. —— 
KBAR TY / area semi 
QQ E CT en 
outer fe SS Ty a s Oy, 
(a WON Vege, ; he, 
edge os. *, d ewes, ; j 
et oF ey 69 a” : 
fz, ) ne? & absorption 
pete focus 
Bb. 
aY 
fey 
AAS 
outer jse/ 
outer z = 
e _ 
edge ge te 
raphe of Hasse. eS S 
ee . er Fi 
D. 8weEks. 
Fic. 3. Development of a semicircular canal. A, B, C, and D represent 
transverse sections of the superior canal (x 240), taken at corresponding 
points from embryos No. 163, 9 mm.; No. 109, 11 mm.; No. 229, 21 mm., and 
No. 86, 30 mm. Aa, Ab, Ba, and Bb are explanatory drawings of lower 
magnification to show the ear vesicle and the situation and shape of sections 
from which A and B are taken. 
