Fritzsch B, Northcutt R G
Department of Biomedical Sciences, Creighton University, Omaha, NE 68178.
Acta Anat (Basel). 1993;148(2-3):96-109. doi: 10.1159/000147529.
The spinal nerves in amphioxus are compared with the spinal and cranial nerves in lampreys. The dorsal spinal roots in amphioxus are similar to the mixed sensory and motor dorsal roots of many cranial nerves in lampreys but not to the purely sensory dorsal spinal roots in lampreys and gnathostomes. Likewise, cranial nerves V, VII, IX and X in lampreys, and all spinal nerves in amphioxus, lack a separate ventral motor root which is a constant feature of all spinal motor roots in lampreys and other vertebrates. Based on these similarities and differences, it is proposed that cranial and spinal nerves in craniates are independently derived serial homologs of elements of an amphioxus-like ancestral pattern. Further evolution involved the addition of neural crest-derived ganglia to most cranial and all spinal nerves, and the addition of placodally derived ganglia to many cranial nerves. The possible homology of ocular motor nerves is discussed but cannot be resolved owing to the absence of these nerves in hagfishes, which are the only relevant outgroup.
文昌鱼的脊神经与七鳃鳗的脊神经和脑神经进行了比较。文昌鱼的背侧脊神经根类似于七鳃鳗许多脑神经的混合感觉和运动背神经根，但与七鳃鳗和有颌类动物的纯感觉背侧脊神经根不同。同样，七鳃鳗的脑神经V、VII、IX和X，以及文昌鱼的所有脊神经，都没有单独的腹侧运动根，而这是七鳃鳗和其他脊椎动物所有脊神经运动根的一个恒定特征。基于这些异同点，有人提出有头类动物的脑神经和脊神经是类似文昌鱼的祖先模式的元素的独立衍生的系列同源物。进一步的进化包括在大多数脑神经和所有脊神经中添加神经嵴衍生的神经节，以及在许多脑神经中添加板层衍生的神经节。文中讨论了动眼神经可能的同源性，但由于盲鳗（唯一相关的外类群）中没有这些神经，因此无法确定。
