630 
ME. W. K. PARKER ON THE STRUCTURE AND 
cular end of the free mandible (fig. 6, mk. ; it is here drawn separately with the 
hyoid to lessen the complexity of the main figure). Giving off two spurs to coalesce 
with the trabecula, the “ prenarial ” and the pterygo-palatine, the quadrate is of great 
breadth at this part. 
Behind the pterygo-palatine bar, and between the trabecula and pedicle, we have 
a falcate membranous space, the “ subocular fenestra ” (so.f.) ; it is rounded in front, and 
its sharp end runs inwards behind. The eyeball ( e ) rests somewhat outside this space, 
on the mandibular pier. 
The free mandible (fig. 6, mk.) is extremely small as compared with the hyoid 
( c.hy .) ; in the adult the mandible is much the larger of the two. At this stage the 
mandible is very long as compared with that of a common Tadpole (Plate 55. fig. 4, mk.). 
their mouths being so different. It is a slender, terete, sigmoid rod ; the distal end is 
pointed and the articular end dilated. The articular and angular parts are curious ; the 
former is not a notch nor the latter a spur, but the dilated end is excavated above, and 
surrounded by a ridge below. The points of the mandibular rods do not meet, but they 
are connected together by the interposition of a pair of short, terete, inferior labials ( l.l .), 
which differ from those of the Frog’s tadpole (“ Frog’s Skull,” plate v. l.l.), for they do 
not dip into a steep “ mentum,” but lie almost on the same plane as the Meckelian rods. 
Their position may be understood by reference to the full figures (1-3), where it is seen 
that the lower jaw and lip point forward a little beyond the upper lip. 
4. The hyoid arch. — Here there is nothing at present but the homologue of the 
infero-posterior piece of an Osseous Fish’s embryo, the cerato-hyal [c.hy.), with no distinc- 
tion of stylo-hyal above or of hypo-hyal below, and no inter-hyal placed between it and 
the mandibular pier. This huge, broad, solid bar (fig. 6, c.hy.) is typically Batrachian, 
with its rounded condyle on the antero-superior angle, its produced postero-superior 
angle, and its broad, pedate base. The sigmoid hinder margin is scooped on the inner 
side, and the outer side is ridgy. 
The narrow helve of a thick-bladed trowel of cartilage separates and unites the hyoid 
cornua. The solid blade is lozenge-shaped; it is the 1st basibranchial ( b.br .). The 
helve is the continuous basihyal ( b.h .). In the Common Frog (op. cit. plate v. fig. 5) 
the basihyal is a small, distinct nucleus : the difference is, a little more differentiation 
in the common type. 
5. The auditory capsules. — These “ paraneurals ” are so remarkably modified by carti- 
laginous outgrowths that they present no easy problem to one coming to them fresh from 
the common kinds. As in the fourth stage of the Toad (Plate 55. fig. 5), the fenestra ovalis 
is opening, but is only filled with indifferent tissue (Plate 56. fig. 5 ,fs.o.). Behind and 
mesiad of that fossa the sacculus is marked out as a lesser oval within the large oval of the 
capsule. Above (fig. 4), the semicircular canals (see, also, next stage, a.s.c., h.s.c.,p.s.c.) are 
seen to be large, and shine through the translucent cartilage. The tegmen tympani (t.ty.) 
projects as a uniform lobe behind the capsule, then narrows to the middle, and then 
widens again. Now, however, it grows from the whole fore margin of the capsule, wedging 
