DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
255 
and each of these gives off four rudimentary true, or intra-branchial, cartilages—small 
“ cerato-branchials ”—with, as is the case in the hyoid, at present, no upper element. 
This inferior, arrested, intra-bran chial framework is covered with a “ lower velum,” 
and the projection of the four pairs of rudimentary cerato-branchials makes it have a 
crenate margin (Plate 1, fig. 4); it is the broad rudiment of the membrane which 
runs under the pharynx in the Lamprey at the entrance of the “branchial canal;” 
the copious growths of gill-tufts on each side, divided by the three clefts, lie under it, 
partially covered. 
All these larval structures may exist in the chondrocranium before the Petromyzine 
skull is modified either by outer or inner bones, and the skull of the larva explains, 
and is explained by, the skull of Petromyzon and its congeners. 
To the Morphologist there is, here, a pause ; but, in fact, in the growth of the 
Tadpole’s skull, there is none ; changes begin soon, and the work of transformation 
then goes on steadily. 
B. b.—Perfect chondrocranium—before the formation of bony centres—in 
the “ Aglossa.” 
The chondrocranium of the larval Dactyletlira (Phil. Trans., 1876, Plate 56) is 
extremely flat and outspread ; it has all the essential parts of a Batrachian larval skull, 
nevertheless. Its form is almost triangular, with the base in front; and although the 
condyles of the cpradrate are carried forwards almost as far as the trabecular horns, they 
are a great distance apart. Even behind, the skull is greatly widened by lateral out¬ 
growths of cartilage, a wide “ tegmen tympani ” already growing from each auditory 
capsule ; and from this, and confluent with it, a very large ear-shaped “ spiracular ” 
cartilage, which spreads wider than, and almost touches the base of, the small orbitar 
process, and the hinge for the cerato-hyal. The suspensoria, also, are wide bands 
running, without an outbend, forwards and gently outwards, to the front of the orbitar 
process. They then bend inwards and are confluent by a very wide band with the 
trabeculae, each band being pterygo-palatine and pre-palatine all in one plate. As in 
Skates, the trabeculae are enormous ; they are separated from the suspensoria by a very 
narrow subocular fenestra, and rise as convexo-concave shells, converging at the hinder 
third of the interorbital region to finish the cranial cavity. As in Skates, however, 
there is a long hollow from it into the nasal trough, which soon widens again. The 
cornua trabeculae are stretched out, as wide arms, in front, and their free end is 
confluent with the pre-palatine spur. They are narrowish bands, and curve round 
the front of nasal passages which are near the frontal margin, but very wide apart. 
Their fore margin shows no notch, for they are completely fused together by a large, 
but indistinct, inter-trabecular tract. The continuous cartilaginous labial, in front of 
the cornua, is partly confluent with them, and runs wider out ; it is the same as the 
“anterior dorsal cartilage” of the Lamprey; the “angular cartilage ” of that Fish is 
