opposite movement of all the above-mentioned elements of the maxillary segment of the craniun 

 takes place. 



various forms of lizards, there are essential differences in the peculiarities 

 in the composition of the various sections of the maxillary segment (cf. 

 ds ot lizards studied fall primarily into two groups: (l) C yclura . Aqatna . 

 , in which the palatal unit is a solid shaft [corej participating in cranial 

 ible integer [whole unit] — unquestionably a more primitive stage; (2) Eumeces , 



Gecko . Gymnodactylus . and Zonurus . in which the palatine unit is articulated 

 oidal juncture to the anterior and posterior parts, movable relative to one 



the first group, the palato-pterygoi dai articulation is a suture running as 

 from postero-anteri orly medially and solidly uniting the two bones (Fig. 2), 

 cond group, a very loose syndesmosis runs more directly laterally [ transversel yj, 

 und the transverse axis (Fig. i) . In geckos, the palatine bone and the 



directly, being separated by loose connective tissue (mentioned by Lakjer, 

 he second group, during retraction, the palatine section is more or less 

 n of the palatal-pterygoidal articulation is raised, and the descending 

 es is decreased. 



-- Table, p. 1402 — 



--p. 1403 — 



The interior movement of the palatine section in lizards of the second group is correlated with the 

 greater role of mesokinesis in the amphikinetic skull (Versluys terminology) than in lizards of 

 the first group and is in general also correlated with the greater development of kinesis. 



Within both groups of lizards there are some more pronounced differences among the various 

 forms. Thus, in Cyclura (Fig. l) and Aqama . the 



However, among the 

 of cranial kinesis and 

 table). First, the kin 

 Lacerta , and Oph i saurus 

 movements as an indivis 

 Varanus . Tera tosc i ncus , 

 along the palato-pteryg 

 another. In lizards of 

 a whole very obliquely 

 while lizards of the se 

 permitting rotation aro 

 pterygoid hardly adjoin 

 I927). in lizards of t 

 bent upward: the regio 

 angle between these bon 



ostorbital bones are closely joined not 

 11 the other forms, but with the latera 

 acerta . the link between the quadrate b 

 n the amphikinetic skull, movements aro 

 elatively weak. The most pronounced di 

 ivision and the upper temporal arches i 

 ygomatic bone is closely connected with 

 noted by Frazzetta), and has elements o 

 he premaxillary bone in relation to the 

 s predominantly around the mesokinetic 

 evertheless, contrary to the opinion of 

 Figs. J-i) skull is the most kinetic am 

 ogether along the central part of the s 

 xceed i ngly mob i le. 



-fig. 5- 



he lateral element of the parietal division as in 

 of the snout, and take part in its movements. In 

 pterygoid (mentioned by Frazzetta) is very lax and 

 metakinetic axis predom inate— mesok inet i sm is 

 ess of movements of the central part of the parietal 

 certa and Oph i saurus . In Varanus , (Fig. 5) * ne 

 latine division and takes part in its movements 

 hokinetism (Hofer, I960); i.e., the movability of 



In the amphikinetic skull of Varanus , movement 

 he parietal division shifts very little (but shifts 

 with respect to the occipital segment. The qecko 

 skulls of the forms studied: the vomers move 

 heir articulation with the palatine bones is 



If we illustrate in the lizard skull lateral view, in a very simplified pattern, the leverage 

 mechanism, in which straight lines represent individual units of the latter (movable only in 

 relation to other units of the skull) and circles to represent the transverse axes around which 

 the possible rotations of these units take place (not unlike the sketches Frazzetta presented for 

 Varanus ). then we obtain the following fundamental variants of the mechanisms (Fig. 6). In Varanus, 

 in contrast to the simplified diagram of Frazzetta, we notice lines of flexion [folding] between 

 the nasal and premaxillary bones, between the vomer and the premaxillary bones, and between the 

 palatines and pterygoids. As is seen in the diagram, the cranial mechanism of Varanus is unique 

 and significantly different from the primitive forms of cranial mechanisms to which lizards of 

 the first group (among the forms studied) stand closest of all, especially Cyclura . 



KINESIS IN L IVING L IZARDS 



MOVING FORCES OF CRANIAL KINESIS 



Hofer (i960) correctly pointed out that the anatomical data on the possibilities of motion 

 in the skull, like data on kinesis, obtained on alcoholic connective-tissue preparations, cannot 

 show the actual presence of correspondingly active motion in the cranium during the life of the 

 animal, but show only the possibility of passive [enforcedj motion. 



--p. 1404 — 



