The Foot-prints of the Creator : $b or, The Asterolepis of Stromness
John Stuart Mill · en
Of all the cerebral bucklers of the first ganoid period, that which
best bears comparison with the cranial front of the cod is the buckler
of the _Coccosteus_, (fig. 11.) The general proportions of this portion
of the ancient Cephalaspian head differ very considerably from those of
the corresponding part in the modern cycloid one; but in their larger
divisions, the modern and the ancient answer bone to bone. Three osseous
plates in the _Coccosteus_, A, C, I, the homologues, apparently, of the
occipital, frontal, and nasal bones, range along the medial line. The
apparent homologues of the parietals, B, B, occupy the same position
of lateral displacement as the parietals of the cod and of so many
other fishes. The posterior frontals, F, and the anterior frontals,
D, also occupy places relatively the same, though the latter, which
are of greater proportional size, encroach much further, laterally and
posteriorly, on the superior frontal C, C, C, and sweep entirely round
the upper half of the eye orbits, 2, 2. The apparent homologue of the
mastoid bone, E, which also occupies its proper place, joins posteriorly
to a little plate, a, imperfectly separated in most specimens from the
parietal, but which seems to represent the par-occipital bone; and it is
a curious circumstance, that as, in many of the osseous fishes, it is to
these bones that the forks of the scapular arch are attached, they unite
in the _Coccosteus_ in furnishing, in like manner, a point of attachment
to the cuirass which covered the upper part of the creature’s body. Of
the true internal skull of the _Coccosteus_ there remains not a vestige
Like that of the sturgeon, it must have been a perishable cartilaginous
box.
[Illustration: Fig. 12.
CRANIAL BUCKLER OF OSTEOLEPIS.]