164 
MR. W. K. PARKER ON THE STRUCTURE AND 
The “ suprahyomandibular” (fig. 3, s.hm.) has become a free plate of cartilage of a tri- 
foliate form ; and the hyoidean cornu, besides being longer and narrower, is acquiring a 
greater projection of the supero-posterior angle, whilst the condyloid part is becoming 
more loosely attached to the glenoid facet on the postero-internal face of the suspensorium. 
But the most remarkable changes have been suffered by the branchial arches, as may 
be seen by comparing their condition in the fourth stage with what is depicted in this 
(Plate V. figs. 1 & 5, and Plate VII. fig. 3). The first and fourth arches are no longer 
carpelliform pouches, but are narrow bands, and all four of these bars are much attenuated. 
The continuous “ pharyngo-branchial” tract now sends upwards six spurs or lobes; the 
third and fourth arches are quite free below, and the “ hypobranchial” base of the first 
and second arches has become narrow and thick ( li.br .). Moreover the hyoid cornua, 
the basihyal, the basibranchial, and the hypobranchial bars have all coalesced. These 
are some of the most important modifications of the branchial system preparatory to its 
thorough abortion. 
Seventh Stage. — Young Frogs with tails reduced to a mere stump. 
The metamorphic changes which for the past few days had gone on with intense 
activity have now produced most interesting results, many of the morphological condi- 
tions being now entirely removed from what can be seen in ichthyic types. 
Many of these changes were fairly begun in the last stage ; but in this further condition 
they make a very near approach to what is essential to the adult Frog only, or princi- 
pally, being modified in the old Frog by increased size. 
Beginning, as in the last stage, with the osseous plates that surround the cartilaginous 
basis, we find that the parietals and frontals (Plate VII. fig. 5, and Plate VIII. fig. 1 ,p.f.) 
have begun to coalesce; the frontals do not quite roof-in the great fontanelle ( fo .) in 
front ; and the parietals seem entirely to overlie a cartilaginous roof ; the cartilage, how- 
ever, is imperfect beneath the centre of each bone. The nasals (n.) are now much longer 
semilunar plates ; and the premaxillaries and maxillaries have equally advanced : the 
former ( pm.x .) have now a well-developed nasal and palatal process ; and the latter (m.x.) 
is forming its ascending or facial plate. Above the plate is seen a small shell-like plate 
of bone which helps to form a floor to the nostril (Plate VII. fig. 5, and Plate VIII. fig. 1, 
s.mx ) ; this is the so-called turbinal, my “ septo-maxillary.” 
In the Frog this bone is severed from the vomer by the subnasal cartilaginous plate 
(Plate VII. fig. 6, s.n.l). In the adult the “ septo-maxillary” finds its way nearly through 
the nasal passage ; but in the young Frog it is best seen from the outside. The squa- 
mosal (Plate VII. fig. 5, sg .) begins to take on its typical character, the upper part 
having acquired more of a transverse direction ; it is also much thicker. 
The upper or supratemporal region of this bone is accurately moulded upon the shell- 
like remnant of the “ orbitar process,” its fore edge overlapping the margin of the carti- 
lage (Plate VII. fig. 5, srp, or.p). The descending process binds down upon the suspen- 
sorium. 
