The palato-pterygo-quadrate bar is united at each end with the cranium, but elsewhere in most cases forms a wide arch standing away from it. The suspensorium is, as in Dipnoi and Holocephali, autostylic. The palato-pterygo-quadrate bar sometimes remains entirely cartilaginous, sometimes its posterior half is ossified forming the quadrate. In connection with it a number of membrane bones are generally developed, viz. the maxillae, premaxillae, palatines, pterygoids, quadratojugals, and squamosals. The pterygoids are, however, sometimes partially formed by the ossification of cartilage. The cartilage of the lower jaw and its investing membrane bones generally have much the same relations as in bony fishes. URODELA. The skulls of the various Urodeles show an interesting series of modifications and differ much from one another, but all agree in the absence of the quadratojugals, in the fact that the palatines lie parallel to the axis of the cranium, and in the large size of the parasphenoid. The lower types _Menobranchus_, _Siren_, _Proteus_, and _Amphiuma_ have longer and narrower skulls than do the higher types. _Menobranchus_ has a very low type of skull which remains throughout life in much the same condition as that of a young tadpole or larval salamander. The roof and floor of the cranium internal to the membrane bones are formed of fibrous tissue, not of well-developed cartilage. The epi-otic regions of the skull are ossified, forming a pair of large bones which lie external to, and distinct from, the exoccipitals. _Proteus_ and the Labyrinthodonts are the only other Amphibia which have these elements separately ossified. The parietals send a pair of long processes forwards along the sides of the frontals. Nasals and maxillae are absent, as is likewise the case in _Proteus_. Teeth are borne on the vomers, premaxillae, pterygoids, dentaries and angulo-splenials. The suspensorium is forwardly directed. The skull of _Siren_ resembles that of _Menobranchus_ in several respects, as in the forward direction of the suspensorium and in the absence of maxillae, but differs in the possession of nasals, in the toothless condition of the premaxillae and dentaries, and in the fusion and dentigerous condition of the vomers and palatines. _Amphiuma_ has a skull which, though narrow and elongated, differs from those of _Menobranchus_, _Proteus_, and _Siren_, and resembles those of higher types in the following respects:-- (1) the suspensorium projects nearly at right angles to the cranium instead of being directed forwards, (2) the maxillae are well developed, and the premaxillae are completely ankylosed together, (3) there are no palatines.