DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
129 
Directly in front of these ethmoidal crests the trabeculae are at their narrowest, are 
closest together, their scooped edge forming the inner margin to the internal nostrils 
(i.n.); the complete hind rim is formed by the crescentic fore edge of the pterygo¬ 
palatine band (p.pg .). In front, the quadrate part of the suspensorium (q.) and the 
trabeculae ( c.tr .) of the same side each send out a bud ( pr.pa .), and these approaching 
growths are united by a fibrous band which finishes the nasal opening. The cornua 
trabeculae maintain their average width up to the frontal wall, but are narrower and 
are longer than usual, diverge very gently, and end in a moderately pedate process, 
which is turned outwards. 
The nasal roofs are not yet cliondrified, the eyeballs have been removed with the 
other soft structures, but the auditory capsules are shown, for they are built into the 
walls of the cranium as side chambers. Below (fig. 2), there is no columella at present, 
but there is an open space, and into this space—the fenestra ovalis—the oval “ stapes ” 
(fig. 2, vb., st.) fits. 
The roof of the future tympanic chamber (t.ty.) is very largely developed ; outside 
the large horizontal canal (h.s.c.) it sends out a small hinder, and a large front, spur; 
the latter is the confluent “spiracular cartilage ” (sp.c.) —the “annulus ” that is to be; it 
just touches and overlaps the otic process (a free elbow now) of the suspensorium ( ot.p .). 
The anterior canal ( ci.s.c .) is covered with bone ( fp .), the posterior (p.s.c.) is naked, 
and bulges gently above and behind. A small circular plate of bone, the ex-occipital 
( e.o .), has grown inside the double nerve-passage (IX., X.) and encloses and subdivides 
it externally. 
The roof is covered to a great extent by the fronto-parietals (fp.) ; these are many 
times larger than those of any other larva at this stage dissected by me (see Plates 
2, 3, 4 ; also Plate 22, figs. 6, 7). 
The two bones are very granular and rugose, quite unlike what is seen in the other 
Tadpoles, they, together, have an emarginate bow-shaped hind edge spread over the 
large ear-capsules up to the horizontal canal ( h.s.c.), which they partly cover, and then 
occupy two-thirds of the interorbital region of the roof. Each bone is deeply notched 
on the inside, half-way ; this is the beginning of the segmentation into two bones ; the 
space thus left bare is roofed by the front part of the hinder tegmen. Behind the 
notch the bones come closer together, ready to form a sagittal suture, in front they 
diverge to their pointed end and have a, rounded inner edge. 
But the parasphenoid (fig. 3 ,pa.s.) is also rugose, pitted, and shows signs of a “ganoid ’’ 
nature ; this is lost in the adult, as if the ]arva retained more of the nature of some 
ancient armed type than the adult. The bone is similar in form to that of Cyclorhamplius 
(fig. 7), and not much larger, relatively ; it is very large in both kinds ; it is broader 
altogether, and notched at the tip ; and the basi-temporal wings are, like the tip, 
less acuminate than in the other Tadpole (fig. 7). 
This condition of the roof and floor-bones in a larval Batrachian just putting forth its 
hind legs is of extreme interest; and the size, massiveness, and sculpturing of these 
MDCCCLXXXI. S 
