The orbital region of the primitive cranium remains cartilaginous, but further forward the cranial cavity is closed by the unpaired sphenethmoid, which forms a ring round the anterior portion of the brain-cavity, hence called "os en ceinture" by some anatomists. The frontals and parietals fuse into one pair of fronto-parietal bones, and these again can fuse together in the middle line; as in Aglossa and _Pelobates_. The palatal portion of the palato-quadrate cartilage is complete, reaching forwards to the sides of the ethmoid region. The curved arch, formed by this cartilage, is covered by the following bones: (1) the quadrato-jugal, reduced to a thin splint which connects the quadrate and squamosal with the posterior end of the maxilla; (2) the pterygoid, always strong, extending from the distal inner corner of the quadrate to the maxilla, sometimes also to the palatine, and with a broad, median process to the parasphenoid, this process covering ventrally most of the otic region; (3) the palatines, which vary considerably in shape and size; they are placed transversely and meet in the middle line; in _Bombinator_ and _Pelodytes_ they are absent. The quadrates are directed transversely and backwards, in conformity with the wide gape of the mouth. The squamosal is always well developed, covering the whole of the quadrate on its outer side; it has a forwardly directed process which ends freely in _Rana_, meets a corresponding process of the maxilla and forms a bony arch with it in _Discoglossus_, _Pelobates_, and others, or {29}is scarcely developed at all, for instance in _Bufo_. In _Pelobates cultripes_ the squamosal is very wide and forms a junction with the fronto-parietals, thus producing a broad bridge across the temporal fossa. The nasal bones are large and meet in the middle line. Frequently they leave a space between them and the diverging anterior portion of the fronto-parietals, through which gap appears part of the dorsal surface of the ethmoid cartilage. A fontanelle between the frontals occurs in most Hylidae, many Cystignathidae, some few Bufonidae, in _Pelodytes_ amongst the Pelobatidae, and in the Discoglossidae.