Kaczmarek Paweł, Hermyt Mateusz, Rupik Weronika
Department of Animal Histology and Embryology, University of Silesia, 9 Bankowa Str, 40-007 Katowice, Poland.
Front Zool. 2017 Jan 13;14:1. doi: 10.1186/s12983-017-0188-y. eCollection 2017.
Snakes are considered to be vomerolfaction specialists. They are members of one of the most diverse groups of vertebrates, Squamata. The vomeronasal organ and the associated structures (such as the lacrimal duct, choanal groove, lamina transversalis anterior and cupola Jacobsoni) of adult lizards and snakes have received much anatomical, histological, physiological and behavioural attention. However, only limited embryological investigation into these structures, constrained to some anatomical or cellular studies and brief surveys, has been carried out thus far. The purpose of this study was, first, to examine the embryonic development of the vomeronasal organ and the associated structures in the grass snake (), using three-dimensional reconstructions based on histological studies, and, second, to compare the obtained results with those presented in known publications on other snakes and lizards.
Five major developmental processes were taken into consideration in this study: separation of the vomeronasal organ from the nasal cavity and its specialization, development of the mushroom body, formation of the lacrimal duct, development of the cupola Jacobsoni and its relation to the vomeronasal nerve, and specialization of the sensory epithelium. Our visualizations showed the VNO in relation to the nasal cavity, choanal groove, lacrimal duct and cupola Jacobsoni at different embryonic stages. We confirmed that the choanal groove disappears gradually, which indicates that this structure is absent in adult grass snakes. On our histological sections, we observed a gradual growth in the height of the columns of the vomeronasal sensory epithelium and widening of the spaces between them.
The main ophidian taxa (Scolecophidia, Henophidia and Caenophidia), just like other squamate clades, seem to be evolutionarily conservative at some levels with respect to the VNO and associated structures morphology. Thus, it was possible to homologize certain embryonic levels of the anatomical and histological complexity, observed in the grass snake, with adult conditions of certain groups of Squamata. This may reflect evolutionary shift in Squamata from visually oriented predators to vomerolfaction specialists. Our descriptions offer material useful for future comparative studies of Squamata, both at their anatomical and histological levels.
蛇被认为是犁鼻嗅觉专家。它们是脊椎动物中最多样化的类群之一——有鳞目动物的成员。成年蜥蜴和蛇的犁鼻器及相关结构（如泪管、鼻后孔沟、前横板和雅各布森穹顶）受到了大量解剖学、组织学、生理学和行为学方面的关注。然而，迄今为止，对这些结构仅进行了有限的胚胎学研究，局限于一些解剖学或细胞研究以及简短的调查。本研究的目的，首先是基于组织学研究，利用三维重建技术，研究草蛇犁鼻器及相关结构的胚胎发育；其次是将所得结果与其他蛇类和蜥蜴的已知出版物中的结果进行比较。
本研究考虑了五个主要发育过程：犁鼻器与鼻腔的分离及其特化、蘑菇体的发育、泪管的形成、雅各布森穹顶的发育及其与犁鼻神经的关系，以及感觉上皮的特化。我们的可视化展示了不同胚胎阶段犁鼻器与鼻腔、鼻后孔沟、泪管和雅各布森穹顶的关系。我们证实鼻后孔沟逐渐消失，这表明成年草蛇中不存在该结构。在我们的组织学切片上，我们观察到犁鼻感觉上皮柱状细胞高度逐渐增加，且它们之间的间隙变宽。
主要的蛇类分类单元（盲蛇亚目、原蛇亚目和新蛇亚目），与其他有鳞目分支一样，在犁鼻器及相关结构形态方面，在某些层面似乎在进化上是保守的。因此，有可能将草蛇中观察到的解剖学和组织学复杂性的某些胚胎水平与某些有鳞目类群的成年状态进行同源性比较。这可能反映了有鳞目从视觉导向的捕食者向犁鼻嗅觉专家的进化转变。我们的描述为未来有鳞目在解剖学和组织学层面的比较研究提供了有用的材料。
