Page:The Osteology of the Reptiles.pdf/83

Rh one the supratemporal or its synonym, the prosquamosal. Yet others both in the past and the present call the outer anterior bone the quadratojugal. The author has given his reasons for believing that the posterior bone is none of these but the tabular instead, the anterior one the squamosal, the quadratojugal absent. He believes that the posterior is the tabular because it occupies the primitive position of that bone in its relations to the interparietal, paroccipital, squamosal, and quadrate. The supratemporal is the first bone to disappear in the temporal region of the Cotylosauria, and its presence has never been positively determined in the Theromorpha and Therapsida.

It is quite possible, however, that both the tabular and supratemporal have disappeared in these reptiles, and that the squamosal has usurped their position and functions; the true supratemporal, however, has no relations with the quadrate as has the bone so called in the skull of the lizards. If so, the bone articulating with it in front and forming the outer boundary of the temporal opening may be the quadratojugal, as was formerly believed and yet is by some. It is a fact, however, that the quadratojugal is a very inconstant bone in all single-arched reptiles otherwise. It is very small in the Theromorpha, is present in only a very few of the Therapsida as more or less of a vestige, and has wholly disappeared in the Sauropterygia. That it should lose its original position at the lower outer side of the quadrate, to form part of the articular surface for its upper end, seems improbable. Furthermore, in the Ichthyosauria (and ?Saphaeosaurus) there is a distinct bone between it and the temporal opening that must be either the squamosal or supratemporal. There is at present no certain solution of the problem.

The skull of the Squamata is at once distinguished from that of all other reptiles by the movable, streptostylic quadrate, secondarily more or less fixed in some forms. The exoccipitals and paroccipitals are always fused; the pterygoids never reach the vomers; the interparietals and either the supratemporals or tabulars, or the quadratojugals, according to the identification, are absent. The teeth are