90 



G. J. de Fej er Vary: 



ossification. I foimd the roof of the skiill to be smooth in quite 

 young specimens,^^) the ridges observable on the homy plates 

 of the ,,pileus" being confined to the integument, which can 

 be easily detached from the skull. Later on the calcareous sub- 

 stance secreted by the derm settles lipon the subjacent cranial 

 bones, forming a crusta calcarea, which, in old specimens, uni- 

 formh' invests the whole cranial siirface, obliterating, as stated 

 above, the superficial limits of the primary dermal bones.^^) In 

 such individuals the deeper corial layers adhere, in consequence 

 of the absolute synostosis of their lime-concretions -with the cranial 

 bones, ver}^ strongly to the roof of the skull, so that the skin 

 cannot be perfecth' ,,stripped off, as is the case in 3'oung specimens. 

 — I am uncertain about the occurrence of a ,,structurar' sculpture of 

 the cranial bones themselves. If such a sculpture occurs it could 

 only be observed in those forms, in which the calcareous Investment 

 of the cranial roof is very feebly developed. 



With respect to the cranial ,,sc ulpt ures", present in a ver\^ 

 large niimber of gigantic fossil Reptilia [Cotylosaiiria, Thcrio- 

 dontia, Saiiropterygia &c. &c.), I can only refer to what has been 

 established on p. 72, when dealing with the same formation in the 

 Batrachians. 



In the Placodontian Placochelys it seems that we may 

 be entitled to look upon the cone-like osseoiis elements occurring 

 in the squamosal and quadratal region, as constituting secondary 

 dermal ossicles. 



The ,,horns" (at least in their distal part) and the tuberosities 

 present on the skull of the Cotylosaurian Elginia might be pre- 

 sumably also referred to secondar}' dermal bones. 



In the Chelonians the dorsal roof of the skull seems to be 

 devoid of noteworth}' secondary dermal ossifications, the one 

 Miolania excepted, in which the ,,horns" belong perhaps to this 

 latter categor}'.^^) 



\Mth respect to the trunk I should hke to observe that the 

 chelonian plastron and carapace undoiibtedly represent secondary 

 exoskeletal features. In some forms a tertiär y exoskeleton has 

 been formed, protecting the degenerated secondary exoskeleton, 

 as in Pscphophorus and Dennochdys coriacca L. The tertiär}' 

 exoskeleton of this latter form seems to be a degenerated offspring 

 of that occurring in Pscphophorus. The median boss-like os- 



I exammed only Alligator, but I presume the same coiiditions to 

 be present in other Croeodihans as well. 



•*^) As regardft the ontogenetical development of the cnista calcarea, 

 the same com*se has been traced in the Batrachians as well (cfr. p. 75). 



The cranial roof of Miolania is sculiDtured. The question whether 

 tliLs sculpture might be attribiited to the presence of a crusta calcarea, or 

 merely to the Osteogenesis of the respective primarj- dermal bones them- 

 selves, remains to be decided by an immediate examination of the original 

 specimens. 



