OF THE SKULL IN SHARKS AND SKATES. 229 
? 
In Birds an “os uncinatum” also often occurs, which is evidently the true homo- 
logue of the antorbital or ethmo-palatine of the Skate and of the Amphibians. Birds 
also possess “ labials.” 
But, to return to the Ichthyopsida, I may mention that the Batrachia, which, like 
the Selachians, appeared most evidently to show that there was no proper distinct 
palatine arch, can now be cited as yielding what appear to me to be convincing proofs 
of the existence of such an arch, whose suspensorial point is the ethmoidal projection 
of the trabecula. 
At first the suspensorium of a Batrachian is quite distinct from the trabecular bar; 
but soon after hatching it becomes attached both before and behind—before to the 
trabecular elbow, and behind to the ethmoidal region of the bar (see ‘‘ Frog’s Skull,” 
pl. 5. figs. 1-4, pg). 
If, in this condition, segmentation had taken place across this short conjugational 
bar, the upper half would have belonged to the trabecula, and the lower half to the 
suspensorium. 
Instead of this, in the Frog, it grows into a long arch, which projects forward beyond 
its ethmoidal part, and is continuous with the suspensorium behind. 
In the Toad, however, (see ‘‘ Batrachian Skull,” part 2, pl. 54. figs. 3, 4), it is seg- 
mented off, not only from its ethmo-trabecular attachment, but also from the pterygoid 
process of the suspensorium, and becomes what its counterpart is at first in the Urodeles 
and Skates, namely a distinct ethmo-palatine visceral piece. 
C. Comparison of the Selachian Skull with that of Ganoids and Teleosteans. 
In the lower kind of Ganoids, such as the Sturgeon (see Month. Micro. Journ., June 1, 
1873, pl. 20, pp. 254-257), the skull becomes /yostylic in the highest degree, and the 
hyomandibular has its lower third segmented off, and separately ossified as a large 
symplectic segment. 
The pterygo-quadrate cartilages are not unlike those of the Skate, but more arched, 
ultimately having three bony tracts in them, namely the pterygoid, palatine, and meso- 
pterygoid. 
But there is only a single counterpart of the two spiracular cartilages. It is an 
arched or conyexo-concave plate, lying over the supero-posterior part of the tubular 
mouth; it is rounded and thick behind, and thin and angular in front, where it fits 
in beween the right and left pterygo-quadrate bars; it is a double “‘ pedicle.” 
In Polypterus (Traquair, Journ. of Anat. and Phys. vol. v. plate 6), the pterygo- 
quadrate is a large bar of cartilage more or less ossified by a metapterygoid, quadrate, 
pterygoid, and mesopterygoid centre. But the top of the metapterygoid is very low 
down ; and the hyomandibular has a small postero-superior osseous centre, and a large 
bony tract which takes in all the rest of the bar, without an inferior “symplectic” 
bony centre. 
VOL. X.—PART Iv. No. 6.—Warch 1st, 1878. 2k 
