102 O. J. de Fe i er Vary: Dermal Bones of the Skull 



19^ In some cases the secondary dermal bones covering the 

 lipper surface of the Lacertilian skiill may be detached from 

 the primary dermal bones to which they adhere. 



20^ In the Genus Lacerta the secondary exoskeletal ossifications 

 are decidedly degenerating in the course of evolution. 



21^ Prof. de Mehely's ,,Archaeolaceyfae" are phylogenetically 

 younger than his ,,Xeolacertae'' , the membraneoiis resp. 

 weak structiire of the ,,archaeolacertian" skull being due to 

 a decrease of ossification (,,degeneration"). 



22^ The evolution of the osseous Reptilian horns, and the homo- 

 logization of the elements by which they are composed, re- 

 mains to be established by future investigations; some of 

 them might consist of an apoph\1:ic basal part, pertaining to 

 primary dermal bones, and an epiph\i:ic distal portion, 

 represented by a secondary dermal ossification. 



23*^ Secondary dermal ossifications occurring under the 

 form of well defined bones are relatively rare and few 

 in number on the skull of the non-lacertilian Reptiles. 

 Such secondary dermal bones are present on the periphery 

 of the parietal bone in Ceratopsidae (0. Dinosauria, Suborder 

 Praedentata) ; the praedental bone of the Praedentata will 

 probably also prove to belong to the same category of ossi- 

 fications. A crusta calcarea is often present. 



24^ In some cases a tertiary dermal ossification may occur 

 on the trunk, as in t]xQ chelonidin Psephophorus, Dermochelys 

 and Toxochelys. 



25^ In Mammals the secondary dermal bones may be re- 

 presented by horns and antlers, or by exoskeletal bone- 

 plates. 



26^ The osseous, but often cartilaginously preformed, 

 distal portion (i. e. the os cornu) of the cavicornian horns 

 and cer\'icornian antlers is epiphytic, belonging thus to 

 the category of the secondary dermal bones. The basal 

 part of the horns and antlers is apophytic andbelongsalways to 

 primary dermal bones. Horns and antlers are — by the 

 bulk • — homologous armaments. 



27^ The exoskeletal bone-plates (secondary dermal bones) 

 protecting the skull in some Mammalians are not as closel}^ 

 attached, i. e. ankylosed to the subjacent primar\' dermal 

 bones as in the lower Vertebrates. 

 Budapest, the 16 of July 1921. 



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