The egg tooth of squamates is a true tooth that allows them to break, tear, or cut the eggshell during hatching. In this clade there are some uncertainties concerning the egg tooth implantation geometry, the number of germs, and their fates during embryonic development. Here, we used X-ray microtomography and light microscopy, focusing on the egg tooth and remaining premaxillary teeth of the sand lizard (Lacerta agilis, Squamata: Unidentata). The developing egg tooth of this species passes through all the classic stages of tooth development. We did not find any evidence that the large size of the egg tooth is related to the merging of two egg tooth germs, which has recently been suggested to occur in snakes. Instead, this feature can be attributed to the delayed formation of the neighbouring regular premaxillary teeth. This might provide more resources to the developing egg tooth. At the last developmental stage, the egg tooth is a large, midline structure, bent forward as in most oviparous Unidentata. It is characterized by pleurodont implantation, and its base is attached to the pleura and a peculiar ridge of the alveolar bone. The attachment tissue contains periodontal ligament-like tissue, acellular cementum-like tissue, and alveolar bone.

中文翻译：

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突破蛋壳：敏捷蜥蜴（Squamata：Unidentata）前上颌牙列的胚胎发育，特别是蛋牙


有鳞动物的蛋齿是真正的牙齿，可以让它们在孵化过程中打破、撕裂或切割蛋壳。在这个进化枝中，关于卵牙植入几何形状、细菌数量及其在胚胎发育过程中的命运存在一些不确定性。在这里，我们使用 X 射线显微断层扫描和光学显微镜，重点观察沙蜥蜴（Lacerta agilis，Squamata：Unidentata）的蛋牙和剩余的前上颌牙齿。该物种正在发育的卵牙经历了牙齿发育的所有经典阶段。我们没有发现任何证据表明蛋牙的大尺寸与两个蛋牙胚的融合有关，最近有人认为这种情况发生在蛇身上。相反，这一特征可归因于相邻规则前上颌牙齿的延迟形成。这可能为正在发育的蛋牙提供更多的资源。在最后的发育阶段，卵齿是一个大的中线结构，像大多数卵生单齿动物一样向前弯曲。其特点是胸膜植入，其基部附着于胸膜和牙槽骨的奇特脊部。附着组织包含牙周膜样组织、脱细胞牙骨质样组织和牙槽骨。