144 Development of Ear and VII-VIII Cranial Nerves 
The development of the endolymphatic appendage and its relation to 
the epithelial stalk formed during the detachment of the ear vesicle from 
the epidermis has excited a considerable controversy out of which certain 
facts have become definitely established. In the first place it is evident 
(Keibel, 99; Alexander, 01; Krause, o1, and 03) that in the chick the 
appendage is formed out of the original union region between epidermis 
and labyrinth anlage, and corresponds to the closing place of the ear 
vesicle, and is its last point of attachment to the surface. On the other 
hand it is also established (Corning, 99; Peter, 00, and Krause, or) 
that in reptiles and amphibia the tip of the appendage does not coincide 
with the point of detachment of the ear vesicle, but is situated somewhat 
more dorsal and proceeds in a course of independent development before 
the detachment of the vesicle is complete. 
In the human embryo the endolymphatic appendage approaches in 
its development more nearly the type seen in amphibia than that in the 
chick. It is not developed until the epidermal stalk, if there ever is 
any such in man, has disappeared. Its anlage is formed by that portion 
of the vesicle wall just dorsal to the seam of closure, forming a rounded 
point on the dorsal edge of the vesicle, thus its tip cannot coincide with 
the point of detachment. Its situation is indicated by the external form 
before there is any apparent differentiation of the wall and can be seen 
in Fig. a, Plate I. By comparison of Figs. a-f, Plate I, it will be 
noticed how, by a process of extension, this diverticulum becomes con- 
verted into the endolymphatic appendage. In the second stage, Figs. D 
and c, the external form of the appendage is more distinctly outlined, 
as a short diverticulum opening widely into the rest of the vesicle. 
In the next older embryo, Figs. d, e, and f, by extension of the tip and 
constriction of its base the appendage begins to assume a typical form. 
The last step in its differentiation consists in the widening of the distal 
end into a flattened pouch or sac, in contrast to the remainder, which 
persists as a narrow duct connecting it with the vestibule, indicated 
in Figs. 1, m, n, Plate I, and well marked in Figs. a, b, c, Plate II. . 
These are the two divisions of the appendage that are distinguished by 
the names endolymphatic sac, and endolymphatic duct. 
During this process of expansion the wall of the appendage which 
originally, like the rest of the primitive vesicle, consists of an epithelium 
of 2-3 layers, is thinned out to a single layer. The thinning out com- 
mences in embryos of about 6 mm. It is at first limited to the lateral 
surface and the extreme tip’ of the appendage, while the median wall 
continues to be 2-3 cells thick. It is not until the embryo is about 18 
