634 
ME. W. K. PAEKEE ON THE STEITCTUEE AND 
tegmen is developed into a distinct “ ear ” behind, and helps to enclose the thymus 
gland ( tm.g .) ; it is then narrow to the middle, and then suddenly spreads into the broad 
awning. Now may be noticed a better differentiation of these parts. The broad part 
of the tegmen in front, opposite the fore margin of the ear-capsule, is not punched out 
just at the edge, as in the last stage, but is snipped out twice as deep, so that the cut 
lip of the tegmen projects largely beyond the (1 thyroid) gland. 
Moreover there is now a good round notch on the fore margin of the flap of the 
tegmen, then a triangular tooth of cartilage, and outside, the long foot-shaped process, 
whose “ heel ” is now pointed. The broad, notched, outer part of the great flap of the 
tegmen is convex above and concave below, and so is the foot ; between the two a more 
definite fossa has appeared, the commencement of a process which will pull asunder the 
outer piece, that it may become the Batrachian “ annulus tympanicus,” a part not homo- 
logous with the tympanic bone. 
Skull of Dactylethra. — Third Stage. Tadpoles at their largest size *. 
The changes remarked in the last stage are still more noticeable in this ; moreover 
there are several new structures. The fore face, in the first stage, was much the wider 
part. Now the greatest breadth is across the auditory region, if we include the tegmina. 
This is a steady growing towards that elbowing outwards of the auditory capsules which 
characterizes the skull of the adult Batrachian ; and as the mandibular pier is attached 
to these masses, this their out-thrusting is a correlate of the immense gape ultimately 
possessed by all the members of this group, glossal or aglossal. 
The much diminished notochord (Plate 57. figs. 3, 4, nc.) is now almost invested by 
the parachordals (iv.) ; it escapes behind between well-formed occipital condyles ( oc.c .), 
and is most exposed above (fig. 3). In front it is hidden, below, by the haft of the 
dagger-shaped parasphenoid (fig. 4, pa.s.), which has now a “ guard,” giving its middle 
part a diamond shape. The foramen magnum ifm.) is now neatly formed, and its sides 
in front of the rim are ossified, both by internal and external bony growth ; these bones 
are the exoccipitals (e.o.) ; they leave, as they always will leave, an unossified upper and 
basal tract ( s.o ., e.o.). Below, these bones are encircling the ninth and tenth nerves 
(9, 10) ; they then form a sickle, the concave edge of which is external, and the blade 
of which nearly reaches the mandibular pedicle (pd.). Now, if we refer to the ossified 
tracts in the chondrosteous skull of the Common Toad (Plate 54. fig. 4, pro., e.o.), we 
shall see that the exoccipital only reaches, below, to the middle of the periotic capsule, 
and that its fore part is ossified by the prootic. 
As in the larva of Pseudis , I note here, in Dactylethra, this generalized pharacter, 
namely, that there is no fair landmark between these bones. From the auditory to the 
nasal sacs the floor of the skull is one wide sheet of cartilage (as in Sharks and Bays) ; 
it is gently convex in the middle, and concave submarginally (fig. 4, tr.). The sides 
are sinuous, and the greatest breadth is opposite to where the parasphenoid ends. 
* See Dr. Guay’s figure (1), Proc. Zool. Soc. Nov. 8, 1864, p. 463. 
