The proatlas, a bone located between the skull and the neural spines of the cervical vertebrae, is best known from reptiles. Most previous studies of the proatlas have centered on its developmental, debating the relationship between the proatlas and the cervical neural arches. The present study was intended as a description of the proatlas in the American alligator (Alligator mississippiensis) and an experimental test of its hypothesized role in venous blood and cerebrospinal fluid (CSF) distribution. In Alligator, the proatlas is chevron‐shaped; ventrally it has a loose connection to the dorsal surface of the first cervical vertebrae, dorsally it has a robust elastic tissue tether on the otoccipital and supraoccipital bones. The ventral surface of the proatlas parallels the dorsal margin of the foramen magnum and rests on the dorsal surface of the spinal venous sinus. Experimental manipulation of the proatlas demonstrated that displacement of the proatlas causes pressure changes in both the spinal venous sinus and the enclosed spinal CSF. The results of this study represent the first demonstration of an explicit functional role for the proatlas, the circulation of fluids between the cranial and spinal compartments of the central nervous system.

中文翻译：

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鳄鱼原寰椎的功能是重新分配静脉血和脑脊液

前寰椎是位于头骨和颈椎神经棘之间的骨头，最出名的是爬行动物。此前大多数对原寰椎的研究都集中在其发育上，争论原寰椎和颈神经弓之间的关系。本研究旨在描述美洲短吻鳄的原寰椎（密西西比短吻鳄）并对其在静脉血和脑脊液（CSF）分布中的假设作用进行实验测试。在鳄鱼，原寰椎呈人字形；在腹侧，它与第一颈椎的背侧表面有松散的连接，在背侧，它在耳枕骨和上枕骨上有坚固的弹性组织系绳。原寰椎的腹侧表面与枕骨大孔的背侧边缘平行，并位于脊髓静脉窦的背侧表面上。对原寰椎的实验操作表明，原寰椎的移位会导致脊髓静脉窦和封闭的脊髓脑脊液中的压力变化。这项研究的结果首次证明了原寰椎（中枢神经系统的颅骨室和脊髓室之间的液体循环）的明确功能作用。