Dermal Bont s of the Skull 



79 



surface of the lamina supraciliaris in Trachysaurus, Tiliqua (Fig. 5) 

 or Zonurus for instance, we will find, especially in younger speci- 

 mens, that the osseous substance constituting the single plates is 

 not uniform, each plate consisting of small polygonous 

 Clements. These polygonous elements may be looked upon as 

 representing single areas of ossification, being retraceable to 

 the single centres of ossification from which the development 

 of the larger plates originally proceeded, This very clearly proves 

 that the larger osseous plates were built up by the fusion of 

 smaller dermal bones, a fact which is in füll accordance with 

 the natural course of the formation and gradual extension 

 of dermal lime concretions.^^) 



The Statement of the lamina supraciliaris belonging to 

 the secondary exoskeleton, as well as its above sketched 

 composition, throw fresh light upon the phylogeny of this cranial 

 Clement, elucidating thus, especially if correlativity is simultan- 

 eously taken into consideration, the following disputed points of 

 the origin of Lacertian forms. 



The one group of the Genus Lacerta, designated by Mr. G. A. 

 Boulenger as ,, Massive Lizards** (Lacerta oceUata Daud , 

 L. Simonyi Stdr. , L. viridis Laur. , L. agilis L., &c.), possesses a 

 strongly ossified skull and, in many species, a completely ossified 

 temporal ,,armour". These features are also present in the other 

 Group, the more or less ,,muralis-\ike'* Lizards, but the ossification 

 is there, generally,^^) considerably weaker, and the number of 

 the osseous plates of the temporal region is generally very much 

 reduced and in many forms the whole temporal armour is wanting. 

 Thus, on account of the secondary dermal bones of the skull, the 

 Genus must be referred, like all the members of the family, to the 

 tectorbital Type. — We have no proof at all of the Lacertidae having 

 derived from Scincoid ancestors, i. e. from forms in which not 

 only the skull, but also the body was provided with secondary 

 dermal bone- plates. It must be admitted, however, that the body of 

 most Lacertilians presenting the same cranial construction as the 

 Lacertidae, i. e. agreeing with them in the presence of a supraciliar y 

 lamina and some temporal bone-plates, is provided with an exo- 

 skeletal armour and thus it may be presumed that the proce- 

 dure, which gave rise to the formation of the dermal ossification 

 on the head in the predecessors of the Lacertidae, was not limited to 



A similar procedure has beert observed with respeet to the develop- 

 ment of the primary dermal bones constituting the upper surface of the 

 skull in the Dipneust and Ci'ossopteryg Fishes (cfr. Abel, Stämme d. 

 Wirbeltiere, p. 178). 



In L. peloponnesiaca D. & B. the skull is strongly osseous, the 

 temporal region is provided with einem fast geschlossenen Hautknochen- 

 panzer", and even the mandibularies bear dermal bone-plates (cfr. Mehely, 

 Ann. Mus. Nat. Hung., V, Budapest, 1907, p. 479). 



^') In Tiliqua these elements are even to be demonstrated on the rugose 

 doreal surface of the lamina supraciliaris (cfr. Fig. 5). 



7. Ilelt 



