Program in Integrative Anatomy, Department of Pathology and Anatomical Sciences, University of Missouri School of Medicine, Columbia, Missouri, USA.
Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, Louisiana, USA.
J Morphol. 2022 Sep;283(9):1210-1230. doi: 10.1002/jmor.21498. Epub 2022 Jul 28.
From the appearance of the vertebrate head, the trigeminal system has played a role in behavioral and ecological adaptation. The trigeminal nerve is the primary cranial somatosensory nerve, also innervating the jaw muscles. In crocodylians, the trigeminal nerve plays a role in modulating the high bite force and unique integumentary sensation. In association with these behaviors, crocodylians are known for large trigeminal nerves, a high volume of trigeminal-innervated musculature, and densely packed, specialized sensory receptors. These innovations also occurred in concert with a restructuring of the lateral braincase wall. These morphologies have previously been investigated in phylogenetic and evolutionary contexts, but an ontogenetic, whole-system investigation of trigeminal tissue and associated musculature, cartilage, and bone is lacking, as is an understanding of developmental timing of morphologies significant to hypotheses of homology. Here, we use contrast-enhanced computed tomography imaging to provide description and analysis of the trigeminal system in an ontogenetic series of Alligator mississippiensis from embryonic to adult form. We explore growth rates and allometric relationships of structures and discuss the significance to hypotheses of homology. We find a high growth rate and allometric trajectory of the trigeminal nerve in comparison to other cranial nerves, likely associated with the large volume of trigeminal musculature and high densities of sensory receptors. We identify a similar trend in the pterygoideus dorsalis muscle, the highest contributor to bite force. We narrow ontogenetic timing of features related to the trigeminal topological paradigm and the undeveloped epipterygoid. Overall, we provide a basis for understanding trigeminal development in crocodylians, which upon comparison across reptiles will reveal ontogenetic origins of morphological variation.
从脊椎动物头部的外观来看，三叉神经系统在行为和生态适应中发挥了作用。三叉神经是主要的颅感觉神经，也为颌肌提供神经支配。在鳄类中，三叉神经在调节高咬合力和独特的表皮感觉中发挥作用。与这些行为相关的是，鳄类具有较大的三叉神经、大量三叉神经支配的肌肉和密集的、专门的感觉感受器。这些创新也伴随着外侧脑壳壁的重构。这些形态结构以前在系统发育和进化背景下进行了研究，但缺乏对三叉组织及其相关肌肉、软骨和骨骼的整体系统发生学研究，也缺乏对与同源假设相关的形态发生发育时间的理解。在这里，我们使用对比增强计算机断层扫描成像技术，对来自胚胎到成年形式的密西西比鳄属的连续发育系列进行了三叉神经系统的描述和分析。我们研究了结构的生长率和异速生长关系，并讨论了其对同源假设的意义。与其他颅神经相比，我们发现三叉神经的生长速度和异速生长轨迹都很高，这可能与三叉肌肉体积大、感觉感受器密度高有关。我们在背翼状肌中发现了类似的趋势，这是咬合力的主要贡献者。我们确定了与三叉神经拓扑范式和未发育的上颚骨相关的特征的相似发育时间。总的来说，我们为理解鳄类三叉神经的发育提供了基础，通过与爬行动物进行比较，将揭示形态变异的发生起源。
