DEVELOPMENT OE THE SKULL IN THE SALMON. 
127 
The former (ppg) are still distinct from the quadrate ( q .) with its projecting “ orbitar 
process;” the “metapterygoid process” is blunt and short, and has not the flattened 
shape it afterwards assumes. The “ hypohyal” has now well applied its hollow upper 
end to the rounded base of the “ cerato-hyal” ( c.li .), and the “ basihyal” is seen to be the 
first of a series of azygous cartilages, which serve to all but the last abortive branchial as 
key-stones. The ascending and lessening branchial arches are becoming stout, and are 
developing their respiratory papillae and their alternating cogs that convert the gill- 
arches into a colander. 
A bird’s-eye view of the primordial skull of a recently hatched Salmon (Plate III. 
fig. 6) shows the advances just spoken of as having been made since the third stage. 
Even now, over the posterior canal, the cartilage is deficient ; the fenestra is a remnant 
of the great space beneath the primary infolding of the “ blastoderm.” 
Fifth Stage. — Salmon-fry of the second week after hatching. 
This stage does not yield in interest to any going before or after it ; taking it for all in 
all the skull has now the most perfect parallelism with that of the culminating “ Ganoids,” 
such, for instance, as the Polypterus. In that light I have seen it, and know not well how 
to describe it otherwise than by using a running comparison with what is seen in that 
fine waif of the seas of the primary epoch. Two of our chief experts in the “ Ganoidei,” 
namely Professors Huxley and Traquair, are of one mind with me in this view ; 
they both see the Ganoid type in this plane of the Salmon’s ascending growth, and 
thus there are three witnesses to attest to the truth of the matter. 
If the reader would follow me in the details of this stage, he should keep open before him 
Dr. Traquair’s “ Cranial Osteology of the Poly ferns ” (Journ. of Anat. andPhys. vol. v. 
pi. G). In this condition of the Salmon’s skull there are no ossifications of the cartilage ; 
the great first hone , the parasphenoid, has appeared, and, as in the lower Ganoids, is of 
huge relative size ; it reaches from between the nasal sacs to beneath and behind the audi- 
tory (see it in dotted outline in Plate IV. fig. 3, in longitudinal section fig. 4, and in trans- 
verse section fig. l,pa.s.). The “ supraethmoidal plate” (fig. 4, eth.) has appeared as a 
fine film of bone in the thickness of the subcutaneous stroma, and the frontals (Plate III. 
fig. 9, f.) are styloid ossifications, forming eaves to the low cranial roof. The thickened 
stroma below the trabecular cornua is not ossified into the “ vomer several, however, 
of the parosteal and ectosteal tracts of the face are already present, and will soon be 
described. What I have to draw the attention to principally, is the greatly altered 
state of the primordial (cartilaginous) cranium ; the ossifications are of secondary im- 
portance. A comparison of the skull as it existed a week before (Plate III. fig. 6, 
upper view) will show the rate and the degree of metamorphic change which has to be 
contemplated now. 
Even now the membranous cranium is growing upward, free of the fore face substruc- 
ture ; the whole of the inflated brain-sac, very large in relative size, as yet, may be 
studied in its own morphological independence. The trabeculce, stretched forward under 
MDCCCLXXIII. s 
