lüO 



G. J. de Fe j erv ary : 



primary dermal bones, is a natural consequence of the skin in the 

 Mammalians not adhering as closely to the roof of the skull as 

 in Fishes, Batrachians and Reptiles. 



Among other Mammalian groups secondary dermal ossifica- 

 tions have not as yet been observed, ,,unless it were in the Cetacea 

 where KuekenthaJ has found traces of a dermal armour/*"^) 



In the fossil Archaeoceti some forms [Zeiiglodon, Delphinopsis) 

 possess secondary dermal ossifications, and Kükenthal, having 

 found such bone-plates in Neophocaena phocaenoides Cuv., pro- 

 nounced the opinion that the . . . Vorfahren der Zahnwale haut- 

 panzertragende Landtiere gewesen sind . . . Die Zahnwale haben 

 sich zu einer Zeit von landbewohnenden Vorfahren abgezweigt, 

 als diese noch einen Hautpanzer trugen, wie ihn z. B. ein Teil der 

 Edentaten vielleicht als altes Erbstück noch jetzt besitzt", "^^j a 

 presumption, which has not been supported, up to now, by any 

 phylogenetical fact. The integument of other Phocaenidae presents 

 but horny (corneous) tubercles. 



Resume. 



P The Vertebrate exoskeleton is formed by dermal i. e. 

 corial bones. 



2^ With respect to the dermal bones we must distinguish two 



kinds: the primary and secondary dermal bones. 

 3^ The ,,membrane" bones of the skull are phylogenetically 



dermal bones, and derived from an ancestral exoskeleton. 



They represent the phylogenetically oldest osseous 



elements. 



4*^ This ancestral exoskeleton is the primary exoskeleton. 

 5^ The ancestral endoskeletonis represented bythe chondro- 

 skeleton. 



6^ The elements of the primary exoskeleton, i. e. the primary 

 dermal bones, withdrew from the corial i. e. connective 

 tissue, by the cells of which they were built up, and entered 

 into a close connexion with the ancestral endoskeleton (i. e. 

 the chondroskeleton), forming with the latter a new skeletal 

 unity: the (more or less) osseous endoskeleton. 



1^ The corium, after the loss of its primary ossifications, secreted, 

 in various Vertebrates, new osseous elements: the secondary 

 dermal bones, which form the secondary exoskeleton. 



8^ Such secondary dermal bones occur on the skull of nu- 

 merous forms, and, especially in some Batrachians and Rep- 

 tiles, in which Classes the skin very closely adheres to the roof 

 of the skull, may coalesce, i. e. coossify with the subjacent 

 primary dermal bones or, in some cases [Anura), with 

 the cartilage bones as well. 



Cf. Gadow, op. cit. p. 208. 

 ") FideHilzheimer, Handbuch d. Biologie d. Wirbelt., II, Stuttgart, 

 1913, p. 629-630. 



