1905.] ANATOMY OF THE FRILLED LIZARD, 19 



to the long axis of the skull. This character, though uniting the 

 three Agaraid genera mentioned, is of no use for diiferentiating 

 the families Agamidse and Iguanidse ; for in Uromastix and 

 Phryiiosoma 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, fi-oni 

 which results a less divergent coarse in the pterygoid3 themselves, 

 and as a consequence a narrower skull. It is interesting to note 

 that the Iguanidas 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, Physlgnatlms, and Amphiholurus 

 possess a long process of the lower jaw behind the articular cavity 

 which is not paralleled in Uromastix. 



Hyoid. — The hyoid of Chlamydosaurus differs in a good many 

 respects from that of Physignathus and Ainphiholarios, 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 Amphiholurus, though there 

 are faint rudiments of them in the former. In Physignathus^ on 

 the other hand, there are two long basibranchial processes, as in 

 Igtumia 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 mai-ked difference in the angles at 

 which the hyoid and branchial lie with regai-d 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 

 Chlamydosatirus the posterior coi-nua are much longer than the 

 anterior cornua than in the other types, I put down to the frill 

 in Chlamydosaurxis which is supported by these posterior cornua. 



There is a final point to which I desire to direct attention 

 which is of some little impoi-tance. In Aviphiholurus, as in the 

 majority of Lizards t, the backwardly and dorsally directed half of 

 the hyoid arch is peifectly continuous with the extremity of the 

 ventral bit of the arch that is attached to the copula. In both 

 Ghlaiinydosaiirus 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 Reptilieu," Zool. Jalirb. (Anat. 

 Abth.) xi. pi. 35. fig. 7 a, and pi. 36. fig. 10 a. 

 f Brouu's ' Thierreichs,' Band vi. (Reptiles) pi. 72. 



2* 



