DEVELOPMENT OP THE SKULL IN THE BATRACHIA. 
81 
ear-shaped flap, notched below, and in front sending down a membranous tract, which 
will soon become cartilage. 
The broad part of this rudimentary “annulus” lies on the swollen unossified 
tegmen tympani, covering the ampulla of the horizontal canal (figs. 6, 7, h.s.c.), and 
forming a bridge over the 7th nerve and the tympano-Eustachian cleft, which opens 
inside, between the suspensorium and the condyle of the pedicle (Plate 12, fig. 3). 
In the recess beneath this double roof the epi-hyal element (columella) has now 
become almost normal in form, but is not yet ossified (figs. 4, G, 7, co.). 
Although relatively so much smaller, it is no hard task to harmonise this element 
with the hyo-mandibular of a Skate, which is developed quite independently of the 
cerato-hyal, and perchance a little after it in point of time. 
There is but one piece of cartilage, for the inter-stapedial segment is not distinct; 
this part is broad, oblique, and wedges in between the ear-sac and the stapes (■ st .), now 
a large lozenge-shaped cartilage. 
The extra-stapedial region is bent downwards, it is ligulate, and retains the breadth 
of the medio-stapedial region; there is no supra-stapedial process. 
The mandible has more than doubled the length it had in the last stage (Plate 12, 
fig. 1, mk.) ; the angular process is reduced greatly, and the loosely swinging hinge 
is quite unlike tha.t of the larva. 
The inferior labial has coalesced with the distal end of Meckel’s cartilage (mlc.), 
but the dentary (cl.) has not yet converted it into a “ mento-Meckelian ” bone. The 
proximal broad end of the lower jaw lies in a thin bony trough, the “ articulare ” (ar .); 
this is developed most on the inside. 
The cerato-hyal (c.hy.) is now attached by the “ hyo-suspensorial ligament ” (fig. 4, 
h.s.l.) to the inside of the suspensorium at its lower third; its styloid region (fig. 4, st.h.) is 
somewhat uncinate, and its hypo-hyal region ( h.hy.) decurved; the basi-hyal has vanished. 
A single rudiment (fig. 5, ex.br.) on each side remains of the four inner and four 
outer branchials ; this plate embraces the basi-branchial ib.br.) which is wider than long, 
and has a crescentic emargination in front. 
The pair of hypo-branchials (h.br.) are not much altered, but their hinder part, which 
sends out rudiments of a third and fourth cerato-branchial (Plate 11, fig. 4, c.br., 3, 4), 
has now become a solid “ horn,” ready to ossify as a “ thyro-hyal ” (t.hy.). 
This is a very instructive stage of the hyo-brancliial apparatus; if it be compared 
with the larval structures (Plate 10, fig. 6 ; and Plate 11, fig. 4), and with those of an 
adult Frog (see in Rana pipiens, Plate 8, fig. 5), we shall see what becomes of the 
copious cartilaginous growths of the larval branchial arches. 
Before leaving this stage I have to remark upon the evidence these changing larval 
skulls supply of the existence of a pre-oral visceral arch in the ethmoidal region. 
Years ago my study of the development of the skull in Birds and osseous Fishes, 
besides what I saw in various kinds of adult Birds, left me in a state of mind that 
scarcely admitted a doubt upon the subject. 
MDCCCLXXXI. 
M 
