The tympanic cavity is bordered in front, above, and below by the squamosal and quadrate, behind by the musculus depressor mandibulae, internally by the otic capsule, and by the cartilage of the cranium between this and the lateral occipital bone. The cavity communicates, however, by the wide and short Eustachian tube with the mouth, the passage being bordered anteriorly by the pterygoid, posteriorly by soft parts. Partly imbedded in these soft tissues is the styloid process or stylohyal, which is attached to the cranium, mostly behind the otic region, and is continued downwards into the anterior horn of the hyoid. The whole partly cartilaginous, ligamentous, and osseous string is, in fact, the entire ventral half of the hyoid arch, while the dorsal half or hyomandibular portion of this, the second visceral arch, is modified into the columellar or auditory chain. The inner end of this chain, the stapes, is inserted into and around the fenestra ovalis of the otic capsule, while the outer end is somewhat T-shaped, and is loosely attached to or near the upper rim of the tympanic ring and to the middle of the tympanic disc. In many Anura this terminal bar can be seen from the outside. The middle portion of the columellar chain is ossified, the rest remains cartilaginous. But the whole chain exhibits various modifications in different genera, especially in the number and the extent of the processes sent out by the outer cartilaginous portion; these are attached in various ways to the tympanum and its rims. The tympanic disc is carried by a cartilaginous ring, which rests against a special process sent out by the quadrate, and is probably itself a differentiation of this element. In some very aquatic genera, but also in _Pelobates_, the {30}tympanic cavity is much reduced, for instance in _Bombinator_, _Liopelma_. In _Batrachophrynus_ not only the cavity, but also the Eustachian tubes are suppressed. In the Aglossa only the two tubes are united into one short but wide median canal, opening at the level of the pterygoids on the roof of the mouth. The lower jaw is remarkable for the possession of mento-Meckelian cartilages, absent only in the Aglossa and Discoglossidae. At first they are much longer than the rest of the jaw; during the larval life they indeed form the functional jaw, and they are now covered with horny sheaths instead of teeth. Owing to the absence of teeth on them, these mento-Meckelian cartilages are later not invested by bone, although in many Anura they ultimately ossify, either retaining their separate nature or fusing partly with the dentary bones. The bulk of the lower jaw, the Meckelian cartilage, becomes invested by the dentary, a small articulare, and an inner angulare, while a splenial element is absent. The dentary itself is mostly reduced to a small dentigerous splint, while the angulare forms by far the greater part of the bony jaw.