Sheverdyukova Hanna V, Kovtun Michail F
Department of Evolutionary Morphology, Schmalhausen Institute of Zoology of NAS of Ukraine, Kyiv, Ukraine.
J Morphol. 2020 Mar;281(3):338-347. doi: 10.1002/jmor.21102. Epub 2020 Jan 27.
The crista sellaris is one of the basic structures of the snake chondrocranium. In embryogenesis it ossifies, forming the basisphenoid. This article describes variations of the crista sellaris, which, in turn, leads to variation in the formation of the basisphenoid in the skull of grass snake Natrix natrix (Serpentes, Colubridae) embryos. Several embryos at different developmental stages are investigated. Embryos from one developmental stage are taken simultaneously from one clutch. Thus, variation of the crista sellaris and basisphenoid in the skull of embryos is discovered, including those from one clutch. In several embryos, the crista sellaris is absent or partially formed. The absence of the crista sellaris does not preclude the formation of the basisphenoid. Based on the observed variations of the crista sellaris, the basisphenoid may have a different origin. In embryos with formed crista sellaris, the basisphenoid develops as a complex endochondral bone from three ossification centers (paired-in the polar cartilages and unpaired in the crista sellaris). In embryos without fully formed crista sellaris the basisphenoid develops as a paired bone of mixed origin: endochondral ossification appears in the polar cartilages, but where the crista sellaris is absent, it is formed by dermal ossification. In general, we observed the absence of the crista sellaris in 15% of studied embryos. We assume that it may be due to a reduction of the orbital-temporal region of the chondrocranium in N. natrix embryos. RESEARCH HIGHLIGHTS: The variation of the crista sellaris and basisphenoid formation in grass snake embryos is revealed. Depending on the presence or absence of the crista sellaris, basisphenoid is formed as a complex chondral bone or as a paired bone of mixed origin.
鞍嵴是蛇软骨颅的基本结构之一。在胚胎发育过程中它会骨化，形成基蝶骨。本文描述了鞍嵴的变异情况，这进而导致草蛇（水游蛇科，游蛇属）胚胎颅骨中基蝶骨形成的变异。对几个不同发育阶段的胚胎进行了研究。从同一窝卵中同时取出处于同一发育阶段的胚胎。由此发现了胚胎颅骨中鞍嵴和基蝶骨的变异情况，包括来自同一窝卵的胚胎。在几个胚胎中，鞍嵴缺失或部分形成。鞍嵴的缺失并不妨碍基蝶骨的形成。基于观察到的鞍嵴变异情况，基蝶骨可能有不同的起源。在鞍嵴已形成的胚胎中，基蝶骨由三个骨化中心发育为复杂的软骨内成骨（两个在极软骨中为成对的，一个在鞍嵴中为不成对的）。在鞍嵴未完全形成的胚胎中，基蝶骨发育为混合起源的成对骨：极软骨中出现软骨内成骨，但在鞍嵴缺失的部位，它由膜内成骨形成。总体而言，在我们研究的胚胎中，15%的胚胎鞍嵴缺失。我们认为这可能是由于草蛇胚胎软骨颅眶颞区域缩小所致。研究亮点：揭示了草蛇胚胎中鞍嵴和基蝶骨形成的变异情况。根据鞍嵴的有无，基蝶骨形成为复杂的软骨内成骨或混合起源的成对骨。
