254 LITLE, [VoL. IX. 
is carried still further, and the epiphysis is now turned a little 
cephalad and has the form of an equilateral triangle (Fig. 19). 
The posterior commissure not only passes further into the 
thalamocoel, but the fold which separates the mesencephalon 
from the thalamencephalon has been carried further into the 
brain cavity in a caudo-ventral direction. The epiphysis in 
shifting its position has become bent near its middle, so that 
while as a whole it is turned cephalad, its distal end is, 
nevertheless, directed caudad (Fig. 19). Along its middle 
there is a narrow cavity, the borders of which are very indis- 
tinct. This cavity extends from the recessus infrapinealis, and 
follows the anterior and dorsal borders of the epiphysis, so that 
it is V shaped with its apex turned cephalad. 
Anterior epiphysial vesicle. — The anterior epiphysial vesicle 
in Amia 10 mm. long is an ellipsoid body which lies close 
against the posterior epiphysial vesicle and to the left of the 
median plane of the brain. It is united to the brain-roof by 
means of a very short stalk which is common to it and the 
posterior vesicle (Fig. 21 £’). Its distal end is turned a little 
cephalad of the common stalk, and its long axis makes an angle 
of a few degrees with a transverse line. Along its middle 
there is a small cavity which communicates with the thala- 
mocoel in a manner very similar to that described in the 
anterior vesicle of Salmo 7 mm. long. In Amia 13 mm. long 
this vesicle extends further cephalad so as to lie directly dorsal 
to the superior commissure and with its long axis nearly 
parallel to the median plane. It still retains its connection 
with the brain in a manner similar to that in Amia 10 mm. 
long. 
In Amia 15 mm. long this connection is severed. By the 
forward growth of the epiphysis the anterior vesicle comes to 
lie against its left side. It is an ovoid mass of cells lying in 
such a position that its long axis is nearly parallel to the 
median plane of the brain. Along its middle there remain 
traces of a cavity. 
flistology. — The histology of the epiphysial vesicles of the 
stages just described is the same as that of the adjacent brain- 
wall. The cells are oval or round and are nearly filled by their 
