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Hyobranchial Skeleton
(Fig. 3.)
Cope (1892) first pointed out the evolutionary importance of the branchial arches among lizards. Camp (1923), after a study of 26 genera in various Lacertilian families, assessed the relative importance of various primitive characters and concluded that the characters of branchial arches are foremost in phylogenetic significance.
In Naultinus and Hoplodactylus, the hyoid and first and second branchial arches persist. Of these three, the hyoid and second branchial arch are attached to the skull. The arches in both genera are similar, except that in Hoplodactylus a definite, though sometimes slight gap appears in the second branchial arch. This occurs between ceratobranchial II (= basibranchial II, Noble, 1921) and epibranchial II, so that the mesial end of the latter lies free in the surrounding muscle.
Naultinus shows an even more primitive condition than Hoplodactylus in that no such gap accurs in the second branchial arch. Thus two complete arches reach the skull. In this respect Naultinus agrees with the condition in the procoelous Eublepharine geckonid, Coleonyx variegatus, described by Noble (1921) as having the most primitive type of lacertilian hyoid apparatus. Apart from the identity.
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Text-fig. 3.—The hyoid apparatus. A, Naultinus elegans. B, Hoplodactylus duvaucelii cbr I; ceratobranchial I, cbr II; ceratobranchial II; ebr I; epibranchial I, ebr II, epibranchial II; h, hyoid arch hc, body of hyoid; pnt, processus entoglossus.
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and relationship of parts, there is a remarkable similarity in the shape of the hyobranchial skeleton in Coleonyx and Naultinus, as also in Hoplodactylus.
The hyoid arch in Naultinus and Hoplodactylus is attached distally to the paroccipital process of the skull, whereas the second epibranchial is attached close to the base of this process. The incomplete first branchial arch in both genera consists of a bony ceratobranchial I, to which is attached the epibranchial I as a curved, bluntly ending piece of cartilage. From the hyoid body itself, a uniformly narrow and elongated processus entoglossus extends forward into the tongue.
At the anterior curve of the hyoid arch in both genera, there projects a short piece of cartilage continuous anteriorly with a further piece at right angles to it. This latter ends in one or more irregularly shaped, blunt projections on each side. Noble (1921) does not illustrate any structure similar to this, but Camp (1923, p. 445) figures the hyoid of Coleonyx variegatus and shows processes from the hyoid arch which are similar to those of Naultinus and Hoplodactylus. Goodrich (1930) illustrates a widening of the arch at this point in Lacerta. Whatever the significance of their development in the above genera, these processes correspond in position to the anterior processes found on the ceratohyal of certain frogs.