The Skull of the Chameleon, Lophosaura ventralis (Gray); some Developmental Stages.



Graphic reconstructions are given of ne cnondrocranium and membrane bone structures of embryos of Lophsaura ventralis (Gray), head-lengths 4.5 and 6.5 mm.; also of the temporal region of an embryo near hatching stage, and a sketch is given of the temporal region of an adult Lophosaura.

The chondrocranium of Lophosaura conforms in essentials to the general lacertilian plan, but has very obvious specializations which appear to be correlated with the large size of the orbit and with the adaptations of the feeding mechanism with its large tongue. The specializations are the telescoping of the ethmoidal region, the exceptional height of the interorbital septum and the reduction of the supraseptals, the vestigial condition of the ascending process, and the degeneration of the joint between the basitrabeeular process and the pterygoid bone.

Although the basitrabecular joint is akinetic, yet tho quadrate is fully streptastylic and widely separated from the jugal.

The bony casque structure at the back of the skull is formed by the parietal processes which meet in the dorsal median line and extend backwards in a prominent roof or crest. The squamosals are also elongated and the superior temporal fossa enlarged, but Lophosaura differs from Chameleo in that the squamosals are separated by the parietal crest instead of extending with the parietal rod; in Chameleo they almost meet in the median dorsal line.

The casque structure seems to be correlated with the increased jaw muscle development associated with the streptostylism of the quadrate; with the rigid upper jaw and the akinetism of the akinetism joint these muscles give a rapid snapping action to the jaws which is associated with the tongue mechanism.

Lophosaura has a tiny tabular (supratemporal) wedged between the squamosal, the quadrate, and the paroccipital process; it is a bone of the occiput.

The problem of the temporal bones in lizards is fully discussed and the differing view-points of Broom, de Beer and Parrington, Gaupp, and Watson (1914) are tabulated.