250 BEATRICE WHITESIDE 
two sides unite in the middorsal line. From this point the two 
sacci run together in a caudal direction, giving the appearance of 
an unpaired structure. They leave the cranial cavity through 
the foramen occipitale and extend inside the canalis vertebralis 
to the region of the seventh vertebra, where the two halves part 
again. ‘Through each intervertebral foramen processes emerge 
which envelop the spinal ganglia. The extreme posterior end 
of each saccus is formed by the calcareous sacs on the spinal 
ganglia IX and X. 
The above description corresponds with the one given by Gaupp 
(07) for the adult frog. Other investigators have maintained 
that the expansion of the saccus endolymphaticus varies in 
different specimens. Gaupp explains this as follows: 
Die einzelnen Teile des Saccus endolymphaticus sind nur dann gut 
zu erkennen, wenn sie mit der charakteristischen milchweissen Fluessig- 
keit gefuellt sind. Der Fuellungszustand wechselt aber, und so kann 
es leicht kommen, dass einzelne Teile nicht sichtbar sind. Dies mag 
wohl der Grund sein, wenn der Saccus gelegentlich eine geringere Aus- 
dehnung zu besitzen scheint. 
I should like to emphasize the fact that, in the larvae and very 
young frogs, some parts of the saccus are invariably quite full 
of calcareous matter, whereas other parts contain only a very 
small amount. The greatest accumulation is always to be 
found in that part of the saccus which surrounds the ganglion 
prooticum commune and the hypophysis and in the part which 
lies on the roof of the fourth ventricle. The partes spinales and 
the calcareous sacs contain a fair amount, while I could observe 
only very few crystals in the anterior cranial part and in the 
processus ascendens anterior and posterior. 
The differentiation of the saccus endolymphaticus into small 
tubuli has progressed so far that each part of that very extensive 
organ consists of many such structures. They are so numerous 
that a description of each one would lead us too far. Some facts, 
however, must be noticed. In the region of the foramen endolym- 
phaticum, the saccus is an undivided sac, which, however, imme- 
diately in front and in back of this aperture, divides into many 
