DEVELOPMENT OF THE SACCUS ENDOLYMPHATICUS 241 
foramen endolymphaticum, it runs dorsal to the plexus of the 
fourth ventricle into the region of the cerebellum. ‘There it 
turns to the side and runs lateral to the brain as far as the anterior 
end of the lobi optici, where it ends. Its largest voluminal 
development is found in the region of the foramen endolymphati- 
cum, where it is very broad, covering a large part of the roof of 
the fourth ventricle. It narrows cranially. There is as yet no 
connection between the saccus of the right side and that of the 
- m.obl, 
fa 
* et: 
“ch. <7 4 
v. tse dt. tse.” 
Fig.4 Transverse section through the head of a larva. (Stage III.) Pos- 
terior part of the medulla oblongata. m.obl., medulla oblongata. 
Fig.5 Transverse section through the head ofa larva. (Stage III.) Laby- 
rinth region. d.t., point where saccus endolymphaticus divides; f.s.e., tubuli of 
saccus endolymphaticus; v, blood vessel. 
left. The part of the saccus which is situated behind the foramen 
endolymphaticum lies dorsal to the brain. It tapers in a caudal 
direction to a still larger degree than was the case in its anterior 
part. Here, too, the saccus of the one side is separated from 
that of the other (fig. 4), and there is no indication of the joining 
of the two sacci, such as occurs some time later in the region of 
the posterior end of the fourth ventricle (compare fig. 7). 
The histological differentiation shows no further development 
than the preceding stages. The saccus is lined with the typical 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 30, NO. 2 
