16 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
the future ethmoid, nearly into halves. The line falls midway between 
the two arms of the trabecule, where they diverge to allow space 
for the pituitary body. In front the ethmoidal mass overlaps slightly, 
on either side, Meckel’s cartilage a little behind its points of sharpest 
curvature. 
In the flatfishes there is no distinct “ tentorium,” or tegmen cranii, 
extending backward from the ethmoid to roof over the front part of the 
brain case, as there is in the salmon. 
b. Stage IL, 
Between Stages I. and II. there is an interval of six weeks and the 
manner of differentiation of the many cartilages and projections found 
---~-~- trb. sworb. s. p. 
trb. sword. dz. _... . i 
«tan trd. sword. 8. a- 
ees 10S’ Cli. 
$3). : ~~ se: t’cis. eth. s. 
Weis. eth. dz. =: _ Ne... Mi ec’eth. 
: ea2ert! orb. a. 
hy-md. ___. | pt-pal. dz. 
ser y ba-hy. 
| 
E dort mk. 
Fie. A. 
Oblique view of the facial cartilages of P. americanus, Stage II. Photographed 
from a wax model (Born’s method) seen from a point midway between sagit- 
tal and transverse planes and about 30° above the horizontal plane. X 75. 
For meaning of lettering, see Abbreviations under Explanation of Plates. 
in Stage II. (Fig. A and Plate 2, Fig. 10) cannot be traced here. 
Figure 10 is a dorsal view of the facial cartilages of this stage. But, 
as it gives a less complete view than the model of the same specimen 
(Fig. A), I call attention to the two supraorbital bars only — the com- 
plete one on the right (trd. sworb. dx.), fastened to the right ethmoid 
wing, and the two parts (a. and p.) of the left one, between which is 
| 
| 
| 
