ANURA. In Anura the skull is very short and wide owing to the transverse position of the suspensorium. There is often a small ossification representing the quadrate. Sometimes as in _Hyla_ and _Alytes_ there is a fronto-parietal fontanelle.
As compared with the skull in Urodela the chief characteristics of the skull of Anura are:--
2. the union of the frontals and parietals on each side,
3. the occasional occurrence of small supra- and basi-occipitals,
4. the backward growth of the maxillae and its connection with the suspensorium by means of the quadratojugal,
5. the dagger-like shape of the parasphenoid,
6. the occurrence of a definite tympanic cavity,
7. the frequent occurrence of a predentary or mento-meckelian ossification in the mandible.
The skull of _Pipa_ is abnormal, being greatly flattened and containing little cartilage. The fronto-parietals are fused, and there is no sphenethmoid. The quadrates are well developed and the squamosals and parasphenoid differ much from those of other Anura.
In larval Amphibia the hyoid and four branchial arches are generally present, and in adult Ichthyoidea they are frequently almost as well represented as in the larva, and are of use in strengthening the swallowing apparatus. They are very well seen in _Siredon_, and consist of a hyoid attached by ligaments to the suspensorium, followed by four branchial arches of which the first and second are united by a copula (fig. 29, D, 8), while the third and fourth are not. The hyoid is not always the largest and best preserved of the arches, for sometimes as in _Spelerpes_ one of the branchials is far larger than the hyoid. Four branchial arches occur in _Siren_ as in _Siredon_, but in _Proteus_ there are only three.
In some larval Labyrinthodontia (_Branchiosaurus_) four branchial arches are known to occur, and their arrangement is almost precisely similar to that in _Siredon_.
In Gymnophiona the remains of only three branchial arches occur in addition to the hyoid. The four arches are all very similar to one another, each consists of a curved rod of uniform diameter throughout. The hyoid is united with the first branchial arch, but has no attachment to the cranium.
In larval Anura (fig. 29, C) the arrangement of the hyoid and branchial arches is much as in Urodela. In the adult, however, the ventral parts of all the arches unite, forming a compact structure, the _basilingual plate_ (fig. 29, B, 1).