DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
63 
The hinder bony centres (e.o., pr.o .) are just such as would be found in a Common 
Frog two-thirds grown; now, a considerable amount of roof, door, and periotic capsules 
are soft. So also the “girdle-bone ” (eth.) is not of great extent, it hardly reaches half 
way to the large optic fenestra (II.); from this space to the foramen ovale (V.) the wall 
is also unossified. The palato-suspensorial arch, and its ectosteal plates {pa., pg.), 
are quite normal; the condyles of the quadrate are very large, and the cartilage at 
that part is but little affected by the quadrato-jugals (q.j.). The pedicles are wide 
apart, and well developed ; the Eustachian passages (eu.) are large and oblique. 
The annulus (a.ty.) is moderate and complete. The stapes (Plate 14, fig. 10, st .) is 
large, thick, and oval; the medio-stapedial (■ m.st.) fits inside it by a decurved unossified 
lobe; but the inter-stapedial is not distinct. The medio-stapedial is therefore large 
behind ; it is straight, and joins on to the narrow stalk of a broadly spatulate extra- 
stapedial (e.st.), which becomes double on its inner face, giving off a strong ligulate 
supra-stapedial (s.st.) which is confluent with the “tegmen” above. The stylo-hyal 
part of the hyoid band {st.h. ) articulates with the floor of the tympanium, and turning 
round, borders the Eustachian opening {eu.). 
The investing bones, one and all, are extremely like those of the type; there is a 
septo-maxillary on each side, but it is small. 
The mandible shows in the dentary (fig. 7, d.) very little of the crest ; yet in 
old individuals the mandible is high at that part, and also somewhat hooked at the 
synchondrosis, like an old male Salmon. 
The hyo-branchial plate (fig. 8) is normal, but its lateral lobes are badly developed. 
15 (continued).—(B) Tomopterna breviceps .— Adult female, 2 inches long. Ceylon. 
The distinction between the skull of the half-grown young of this species and the 
young of a Common Frog of the same age, is slight as compared with what is seen in 
their adult condition (Plate 15, figs. 1-4; and Phil. Trans., 1871, Plate 9). 
The facial outline now forms half a rather short ellipse, and the greatest breadth is 
nearly one-fourth more than the length ; moreover, this is one of the highest (or 
deepest) of the skulls in the whole Order. 
Indeed, this Frog is an isomorph in respect of its short deep head and its thorough 
want of neck of the most remarkable Toads of the same (the Oriental) territory, e.g., 
Callula, Diplopelma, Cacopus. 
This, again, is an instance of what is seen in the main geographical territories, viz.: 
that some particular modification characterises the members of very different “Families” 
of the same Order, as if the Anurous type had, in each territory, broken up into 
groups isomorphic of, but not immediately related {genetically) to, those of other terri¬ 
tories. Thus from a generalised root-form, in territories wide apart, there may have 
sprung, in each place, independently, Frogs with teeth and Toads without teeth; 
