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Snakes differ from the other vertebrates with their hyperkinetic skull. To establish the developmental features of the skull bones, involved in prey capture and ingestion, the Grass snake Natrix natrix (Serpentes, Colubridae) embryos are studied at all the successive stages of embryogenesis. Thirty‐five N. natrix embryos are examined. Twenty embryos are studied with histological methods; fifteen embryos are cleared and double‐stained with alizarin red and alcian blue. The sequence of appearance and formation of the upper and lower jaw bones, palatal complex and associated bones is described in accordance with the table of developmental stages. New features in the ossification mode of some bones are revealed: each bone, namely, the vomer, septomaxilla and maxilla, is formed from three separate ossification centres. Three ossification centres in the maxilla, two ossification centres in the bodies of the septomaxilla and vomer, as well as the unknown additional ossification centre in the vomer had not been previously described in snake embryos. The new data can be used in further comparative research on the reptile skull development and vertebrate phylogeny.

The theory of filembriogenesis is only an introduction to the problem’s development of ontogeny’ and phylogeny’ relation (hereinafter — «relation»). Discussions as to whether ontogeny creates phylogeny, or vice versa, are devoid of meaning. The opinion of O. Hertwig (Hertwig, 1906) that the ontogeny and phylogeny are two parallel and independent developmental processes is valid only in the first part; thesis about independence distorts the essence of «relation.» According to the authors, one of the essential characteristics of the «relation» is that ontogeny gives the material for phylogeny, and phylogeny renews ontogeny, leading away ontogeny from inbreeding; that ontogeny ensures the life continuity and phylogeny — its differentiation, that is, creates biodiversity; that ontogeny and phylogeny can exist and function only in conjunction or in parallel, changing places (in terms of priority) in the life evolution.

Polar Cartilages and Formation of Crista Sellaris in Grass Snake, Natrix natrix (Ophidia, Colubridae), Chondrocranium at the Early Stages of Embryogenesis. Sheverdyukova H. V.- The initial developmental stages of grass snake’s, Natrix natrix Linnaeus, 1758 chondrocranium are described. Three paired structures form the floor of N. natrix’s neurocranium: cranial trabeculae, polar cartilages, and parachordals. The primordiums of polar cartilages and their independent centers of chondrification are identified at the stage 26 of development for the first time for N. natrix and snakes in general. The participation of these structures in the formation of crista sellaris and carotid foramina is proved.

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