Development of the osteocranium in Natrix natrix (Serpentes, Colubridae) embryogenesis I: development of cranial base and cranial vault

Abstract

The development of cranial base and cranial vault bones at successive stages of embryonic development in Grass snake Natrix natrix (Serpentes, Colubridae) is described in the article. The stages of embryo development are determined by the table of stages of normal development, suggested by Zehr (Copeia 2:322–329, 1962). 35 N. natrix embryos were examined; 20 embryos were studied with histological methods; 15 embryos were cleared and double-stained with alizarin red and alcian blue. The sequence of appearance and formation of cranial base and cranial vault bones are determined. New features in the appearance and mode of ossification of some bones are revealed: the postorbital, parietal bones and basisphenoid are formed from two ossification centers and the prefrontal bone—from three ossification centers; the supraoccipital bone is formed as a paired bone; the laterosphenoid is shown to be formed as a cartilage-replacement bone. The new data I received can be used in further comparative researches on the reptile skull development and studies on reptile phylogeny.