Page:The Osteology of the Reptiles.pdf/84

66 acrodont or pleurodont; the prearticular of the mandibles is always fused with the articular. Other characters are very variable in this extensive order, which is sometimes divided into two or three distinct orders.

In the lizards (Figs. 55, 56) the quadrate articulates above normally with three bones, the squamosal, paroccipital, and a third bone whose homology is yet disputed, but which is usually called the supratemporal. The squamosal may be absent in those lizards without a temporal arch, and rarely in certain degraded burrowing lizards (Fig. 56) the "supratemporal" may also be absent, the quadrate lying against the brain-case and more or less fixed by the pterygoid. The paroccipital usually but not always helps support the quadrate.

As regards the identity of all these bones, there has been great difference of opinion, and there is by no means unanimity at the present time. The tabular, as here identified, has been called the squamosal, supramastoid, supratemporal, and even the paroccipital (opisthotic). The squamosal as here considered has been called the quadratojugal, supratemporal, paraquadrate, squamosal, and prosquamosal. The reasons for their identification as the tabular and squamosal will be found in the discussion of the skull of the Protorosauria.

Below, the quadrate articulates with the pterygoid on the inner side by a rather free joint in most lizards, in some, like the Amphisbaenia (Fig. 56) by a close sutural joint. On the inner side the usually slender stapes abuts against the quadrate (Fig. 55 ). In the mosasaurs there is an elongated suprastapedial process arching backward and often extending to the lower end, enclosing the auditory meatus, as in some turtles.

The tabular (Fig. 55, ta), or supratemporal, at the distal and under side of the parietal process, forming more or less of the boundary of the temporal opening, articulates with the squamosal, paroccipital, and quadrate. In the mosasaurs (Fig. 54 ) only, it has a long internal process, firmly wedged in between the paroccipital and proötic, extending nearly or quite to the semicircular canals. In some lizards the tabular has suffered reduction or has become indistinguishably fused with the squamosal.