20 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the ear capsule substantially as in Stage II., there being just room for 
the eye — now, of course, increased in size — to pass between the front 
end of it and the ethmoid. The right supraorbital becomes a little 
more arched as the fish increases in depth. The wings of the ethmoid 
extend out from the mid-line farther proportionally and are more flat- 
tened antero-posteriorly. Upon the surface of these wings of the eth- 
moid cartilage the ect-ethmoid bones, or pre-frontals, are later formed. 
___trb. sword. s. p. _. ves. eth. dz. 
[mints 2 Braue 
ims-eth. 
| 4, 
: | ; 
tr bE : 
: ee 
7 ) 
pl-pal, siamese ee 
ee —~—lec’eth. 8. 
. ; 
| go. for. olf. s. 
pt-pal. az.-—~ --~- ~------@ wi lert, orb. a. 
iw, ...pt-pal. s. 
ert. mk, dase 
Fie. B. 
ms 
Oblique view of the facial cartilages of P. americanus, Stage III. Photographed from a 
model, as in the case of Fig. A. X circa 75. 
For meaning of lettering, see Abbreviations under Explanation of Plates. 
The gape has been greatly increased by the growth in length of all 
the facial cartilages, but these have not increased in diameter propor- 
tionately. The pterygo-palatine bars, which from the first support the 
upper jaw, in lengthening have come to lie nearly parallel to Meckel’s 
cartilage, and their articulation with the quadrates is so far posterior 
that the one of the left side alone falls within the region modelled. At 
this stage these cartilages are in some instances so reduced in diameter 
toward their posterior ends, as to show in cross sections only one cartilage 
cell. A process from the left wing of the ethmoid has fused with the 
