DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
253 
are the auditory capsules ; large masses of cells, the rudiments of the ganglia of the 
5th and 7th nerves, separate these globes from the pedicles of the suspensoria. 
The eye-balls are not taken into account; the nasal sacs are entirely membranous, 
at present. 
The parts displayed in the dissected head, and in sections through all the parts of 
the head, lend colour to the suggestion that all the three pairs of cartilages are 
serially homologous : I believe this to be quite opposed to the true interpretation 
of the parts; that the inner bands (trabeculae) are prematurely developed, paired, 
axial parts, growing beyond the notochord, but parachordal in their hinder part: 
moreover, in other types, as the “ Urodeles ” and “ Marsipobranchs,” the part embracing 
the notochord is, from the first, much larger than in the “ Anura.” 
B. a .— Perfect chondrocranium: — before the formation of bony centres—in the 
“ Phaneroglossa.” 
The simple cartilaginous bars that were seen at first are soon developed into a 
perfect chondrocranium of the Petromyzine type. 
The cranial notochord, besides its own mesoblastic sheath, which is now and then 
chondrified even in the “ Anura,” becomes enclosed, right and left, between two solid 
bars of cartilage—-the extension, backwards, of the apices of the trabeculae (and not 
as separate plates, as in the “ Urodeles ”); and these two basal plates are fused 
together, for a short distance, in front of the notochord (see Phil. Trans., 1876, Plate 
55, and the figures of larval skulls in the present paper). 
In the nasal region the trabeculae coalesce, and then send their elongated horns 
forwards, and downwards ; in the interorbital region, each bar sends upwards a crest, 
which becomes thick and bulbous near the coalesced part: here we have the beginning 
of the cranial walls, and of the ethmoidal region, or closing-in part of the skull. 
After a while, behind the ear-capsules, a wall, and then a roof, is formed—the occipital 
arch. 
The large, bowed, twice-conjugated suspensoria develop a crest along their outer 
edge, and this grows into a large leafy plate in the ethmoidal region—the “ orbitar 
process,” which may (exceptionally), as in Bufo vulgaris , coalesce with the ethmoid. 
The free mandibles grow larger, form a condyle and an “olecranon,” and carry the 
(suctorial) lower labials between them, as the cornua trabecula carry the upper or 
overlapping labials. 
The third bar (hyoid—second visceral arch) grows more perfect in form, as well as 
gets larger in size, but retains its primitive place under the antorbital region. 
The auditory (parachordal), orbital, and nasal regions are nearly equal in length, 
and the auditory sacs become gradually completely invested with their own cartila¬ 
ginous coat, which takes the form of the swelling and arching cavities within. 
