The lacrymalia are still separate in some Amblystomatinae, e.g. _Ranidens_ and _Hynobius_. A pair of nasalia are generally present, but are absent in _Necturus_, _Proteus_, and _Siren_. The parasphenoid is furnished with teeth in the Plethodontinae and Desmognathinae. Separate palatine bones exist in _Necturus_ and _Proteus_, and in the larva of _Amblystoma_, but in the adult form they fuse with the vomers, producing the vomero-palatines characteristic of the majority of Urodela. {18}The pterygoid bones are most fully developed, so as to reach the vomero-palatines, in the Amblystomatinae, in _Necturus_, and in _Proteus_; they are reduced, so as to leave a gap, in _Cryptobranchus_, and still more in the Salamandrinae; they are absent in _Amphiuma_ and in _Siren_. The quadrates are directed forwards in _Necturus_, _Proteus_, and _Siren_, while in the other Urodela they extend transversely and almost horizontally. The hyomandibular remnant, the so-called operculum, is small, and forms a plate which fits into the fenestra ovalis, extending as a ligamentous process upon the quadrate. The quadrato-jugal elements are reduced to ligaments. In many Salamandrinae the large orbito-temporal space is divided into an orbital and a temporal fossa by an arch which is formed by the meeting of two corresponding processes from the squamosal and frontal bones respectively. This bridge is rarely bony (_Salamandrina_, _Triton_), mostly ligamentous;–apparently a reminiscence of the Stegocephalous condition. The two premaxillary bones are liable to fuse into one, for instance in _Cryptobranchus_, generally in adult Tritons. They are most reduced, and are toothless, in _Siren_. The two maxillary bones are absent only in _Necturus_, _Proteus_, _Typhlomolge_, and _Siren_. Their posterior end is frequently free, loosely connected by ligaments with the pterygoid in _Cryptobranchus_; or with the distal portion of the quadrate, and in this case either just touching it (_Tylototriton_), or forming a broad junction (_Pachytriton_). Each half of the lower jaw consists of a dentary, articular and angulo-splenial. The splenial remains as a separate element in _Siren_; in others only during the larval period. There are no mento-Meckelian elements. SKELETON OF THE ANURA