-p. 1409-- 



their prey by constriction or by poison, and the jaws do not exert mechanical pressure in holding, 

 killing and chewing the prey. 



The reduction of kinesis in chameleons is evidently correlated with feeding on small prey, 

 captured by the aid of the tongue. 



The question of kinesis or akinesis in Sphenodon remains open at this time. Recently Ostrom 

 (1962) showed that in several types of Hatter ia the protractor muscles are well developed and in 

 a mature state. Ostrom suggested that in various populations of Sphenodon , kinesis can be lost or 

 preserved in the adult state depending on the feeding peculiarities of a given population. Our 

 study of the skulls of Hatteria leads to the conclusion that metakinesis in these forms and their 

 ancestors must essentially be distinguished from the scheme of metakinesis proposed by Versluys 

 ( 1 91°» 19 12 )- Versluys proposed that in metakinesis, the maxillary segment of the skull moves as 

 a single unit, in which the palatine arch, the bones of the snout and the skull roof are all 

 rigidly joined to each other. However, the structure of the skull of Ha t ter i a shows that retraction 

 in this form should take place in the abducting elements of the palatine arch (pterygoids, palatines, 

 epi- and ectopt erygo i ds, and vomers). This means that in this metakinetic skull, movement of the 

 lateral parts of the maxillary segment in relation to its central part should take place, similar 

 to those noticed in the amphikinetic lizard skull. Whether during retraction the movements of the 

 palatal arch and the lateral elements of the dermatocran i um are independent, as in lizards, or 

 whether those and others were displaced relative to the middle elements of the maxillary segment, 

 we cannot determine from available museum materials. In any case, retraction of the metakinetic 

 skull type is accompanied by diversion and rotation around the linear axis, lateral margins upward, 

 of elements of the palatine arch, by the lateral part of the superposed skull armor. It seems to 

 us permissible to presume that these movements might be characteristic of the metakinetic skull 

 type in general. But examination of the problems of evolution of cranial kinesis exceeds the scope 

 of the present paper. 



CONCLUSIONS 



(1) Among the various lizard species, there exist essential differences in the peculiarities 

 of cranial kinesis and in the composition of var ious pa rts of the maxillary segment. Cranial 

 kinesis of Varanus. used as the basis for analysis of lizard skull kinesis by Frazzetta (1962), 



is neither the most primitive nor the most prevalent form of cranial kinesis among lizards. 



(2) The most primitive type, among the forms studied, is in the Cyclura . Agama . Lacerta , and 

 Opn : saurus . in which the palatine section of the maxillary segment is a tough core [stout shaftj, 

 taking part in the movements of the skull as a single unit. 



(3) In the presence of strengthening of cranial kinesis in lizards, in the palatine unit 

 there is developed movability of its anterior part in relation to the posterior part. 



(l) The M. pterygo i deus, which functions as a retractor in the cranial mechanism in 

 Frazzetta's opinion, actually in lizards cannot produce any kind of retractor movements by the 

 latter. 



(5) It seems probable that cranial kinesis provides the best means of holding prey [which is 

 trying to escape] in the predators jaws. Protraction can serve to release the teeth of the upper 

 jaw during seizure of prey or in swallowing. 



(6) Kinesis of the skull in its unspecial ized forms is especially advantageous for the 

 universal [generalized] predator feeding on prey [which isj small relative to its own size, but 

 not too small prey. 



(7) Most of all, in the metakinetic type of skull, retraction and protraction of the maxillary 

 segment are accompanied by abduction and adduction of the palatal arches, and the lateral elements 

 of the superposed skull and by their rotation around the longitudinal axes, that is, definite 

 movement taking place within the maxillary segment of the skull, despite the pattern of metaklnetism 

 proposed by Versluys (1910, 1912). 



