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Show 1905.] ANATOMY OF THE FRILLED LIZARD. 19 to the long axis of the skull. This character, though uniting the t nee Agamic! genera mentioned, is of no use for differentiating the families Agamidse and Iguanidae; for in Uromastix and Phrynosoma this bone is directed forwards, as in Varanus and Heloderma. The three genera furthermore agree (to differ from Uromastix) in the comparative shortness of the basipterygoid processes, from which results a less divergent course in the pterygoids themselves, and as a consequence a narrower skull. It is interesting to note that the Iguanidae show a similar pair of contrasts. It is plain from Dr. Busch's figures*, as well as from skulls before me, that Iguana has short basipterygoid processes and that Phrynosoma has long ones. Finally, Chlamydosaurus, Physignathus, and Amphibolurus possess a long process of the lower jaw behind the articular cavity which is not paralleled in Uromastix. Ilyoid.-The hyoid of Chlamydosaurus differs in a good many respects from that of Physignathus and Amphibolurus, as may be seen by a comparison of the accompanying figures (text-figs. 9, 10, pp. 20, 21). The basihyoid sends back no long basibranchial processes in either Chlamydosaurus or Amphibolurus, though there are faint rudiments of them in the former. In Physignathus, on the other hand, there are two long basibranchial processes, as in Iguana and Anolis. I imagine that the absence or presence of these long processes is related to the absence or presence of the " dewlap " in the forms under consideration. In these three Lizards, as in others, the hyoid and branchial arches [i. e. the anterior and posterior cornua] articulate with each other as well as with the median copula at their insertion on to that. There is, however, a marked difference in the angles at which the hyoid and branchial lie with regard to each other. In Chlamydosaurus the two visceral arches are at about right angles to each other where they join the copula: Physignathus is at the other extreme ; the parts in question are nearly in the same straight line. In this particular Amphibolurus comes nearer to Physignathus than to Chlamydosaurus. The fact that in Chlamydosaurus the posterior cornua are much longer than the anterior cornua than in the other types, I put down to the frill in Chlamydosaurus which is supported by these posterior cornua. There is a final point to which I desire to direct attention which is of some little importance. In Amphibolurus, as in the majority of Lizards f, the backwardly and dorsally directed half of the hyoid arch is perfectly continuous with the extremity of the ventral bit of the arch that is attached to the copula. In both Chlamydosaurus and Physignathus the arrangement is as seen in the annexed figures (text-figs. 9, 10, pp. 20, 21), i.e. the ventral half is prolonged dorsally of the point of attachment to it of the * " Beitrag z. Kenntniss d. Gaumenbildung bei den Reptilien," Zool. Jftlnb. (Auat. Abtb.) xi. pi. 35. fig. 7 a, and pi. 36. fig. 10 a. t Bronn's ‘ Thierreichs,' Band vi. (Reptiles) pi. 72. O* |
