DEVELOPMENT OF THE SKULL IN THE BATKACHIA. 
639 
margin; this has changed greatly since the last stage (Plate 57. figs. 3, 4, t.ty., a.t.). 
Nearly separated from the outer crescent, the true “ tegmen,” as seen from above 
(fig. 2, t.ty.), looks as if the valve of a leguminous fruit had grown obliquely from 
the capsule ; and, indeed, this is its shape, for it is convex above and hollow below 
(figs. 2, 3). 
The crescent itself {a.t.) seemed to me at one time to be the early condition of 
the “ extrastapedial” of the adult (Plate 59, e.st.). Supposing the “tegmen” to be 
its stalk, and ready to ossify into the “ medio-stapedial ” and “ interstapedial ” shaft- 
bones, this heart-shaped leaf of cartilage, blade and petiole, seemed all ready to 
become the columella of the adult, and the homologue of the fish’s hyomandibular and 
symplectic *. 
The thyroid gland (fig. 3, tr.g.) lies now beneath the stalk and leaf of cartilage ; I 
have indicated its position by dotted lines. The stapes ( st .) has been teased away from 
the fenestra ovalis {fs.o.) to show its shape, it is irregularly oval and convexo-concave, 
and its outer convex surface is seen to be covered with muscular fibres. 
The fossa (fig. 3), now fairly on the side of the auditory capsule, is only open behind ; 
even the stapes itself is much larger than the fenestra, which is covered by its hinder 
half. 
The new bones now apparent are the vomer, nasals, premaxillaries, maxillaries, 
dentaries, and articulars ; the two latter have been described already. The vomer 
(fig. 3, v.) is semicircular, with the hinder, abrupt edge sinuous ; it invests the apex of 
the huge parasphenoid ( pa.s .). The maxillaries and premaxillaries {mx.,px.) form a 
crescentic row of bones, outside the front of the face, and on their under surface we see 
the teeth. The maxillaries run scarcely twice the extent of the premaxillaries ; the 
latter have already a nasal and a palatine process (figs. 2 & 3, px.). 
The nasals (fig. 2, n.) are large, accurate crescents ; they are margined with a flap of 
membrane on their concave or anterior margin, and this is further margined by a .labial 
(' u.l. b ) ; this complex nostril-cover is behind the external passage (e.n.). Altogether, this 
Toad has its breathing-passages protected by a most complex valvular apparatus. 
The frontals (fig. 2 ,f.) have increased in size, and, save at the hinder margin, are 
well ankylosed together ; the parietals (p.) are parasitic plates, overlapping the frontals. 
By comparison of this half-metamorphosed young specimen with the adult, seeking 
side-lights from more familiar Batrachians, we shall be able now to appreciate the 
remainder of the metamorphic modifications, by which the skull of the Siluroid, and 
almost Chimseroid larva of Dactylethra passes into that of the adult. In its last stage 
we shall find as many notable things as in the larval ; for this type is very contrary, not 
only to the common tongue-bearing types, but also to the other aglossal form, namely, 
Pipa. 
* The merciless rigour of my fellow-labourer Professor Huxley’s criticism has been of the utmost value to me 
in this and in many other cases ; and I am truly grateful for the effect upon me, of the wholesome incisiveness 
of his inborn, logical severity. 
