Song J K, Northcutt R G
Department of Biology, University of Michigan, Ann Arbor.
Brain Behav Evol. 1991;37(1):10-37. doi: 10.1159/000114343.
The lateral-line system of gars consists of superficial neuromasts, which are arranged in lines termed pit lines, canal neuromasts and spiracular organs, which are located within diverticula of the hyoid gill pouch. Both canal and superficial neuromasts possess polarized hair cells whose directional sensitivity parallels the long axis of their respective lines. However, the apical surfaces of canal neuromasts are larger and possess far more hair cells than do those of superficial neuromasts, but superficial neuromasts have longer kinocilia and, presumably, longer cupulae. The receptors of the lateral-line system are innervated by three pairs of cranial nerves: anterior, middle and posterior lateral-line nerves. The anterior lateral-line nerves innervate neuromasts of the supraorbital, infraorbital and preoperculo-mandibular canals as well as dorsally located anterior pit lines, cheek (horizontal, vertical and mandibular) and gular pit lines of superficial neuromasts and the spiracular organ. The middle lateral-line nerves innervate dorsally located middle pit lines and a single neuromast in each temporal canal. The posterior lateral-line nerves innervate dorsally located posterior pit lines, neuromasts of the supratemporal commissures and all remaining postotic and trunk neuromasts. The ganglion of the anterior lateral-line nerve is divided into dorsal and ventral subganglia; the single ganglion of the middle lateral line nerve has no recognizable subdivisions, and the ganglion of the posterior lateral-line nerve consists of rostral and caudal subganglia. Analysis of the roots of these nerves and review of the embryonic origin of their ganglia as well as comparisons with cranial nerves in other anamniotes suggest that the anterior and posterior lateral-line nerves of gars may represent the fusion of four to five separate lateral-line nerves at some stage in vertebrate phylogeny. Thus, with the addition of the middle lateral-line nerve, and the possible existence of a ventral lateral-line nerve of the trunk, it is possible that the earliest jawed vertebrates possessed six or even seven pairs of lateral-line nerves.
雀鳝的侧线系统由表面神经丘组成，这些神经丘排列成称为凹线的线条，以及管神经丘和鳃孔器官，它们位于舌鳃囊的憩室内。管神经丘和表面神经丘都拥有极化毛细胞，其方向敏感性与各自线条的长轴平行。然而，管神经丘的顶端表面更大，拥有的毛细胞比表面神经丘多得多，但表面神经丘有更长的动纤毛，大概还有更长的顶器。侧线系统的感受器由三对脑神经支配：前、中、后外侧线神经。前外侧线神经支配眶上、眶下和前鳃盖下颌管的神经丘，以及背侧的前凹线、脸颊（水平、垂直和下颌）和表面神经丘的喉凹线以及鳃孔器官。中外侧线神经支配背侧的中凹线和每个颞管中的单个神经丘。后外侧线神经支配背侧的后凹线、颞上连合的神经丘以及所有其余的耳后和躯干神经丘。前外侧线神经的神经节分为背侧和腹侧亚神经节；中外侧线神经的单个神经节没有可识别的细分，后外侧线神经的神经节由头侧和尾侧亚神经节组成。对这些神经的根进行分析，并回顾其神经节的胚胎起源，以及与其他无羊膜动物的脑神经进行比较，表明雀鳝的前外侧线神经和后外侧线神经可能代表了脊椎动物系统发育某个阶段四到五条独立侧线神经的融合。因此，加上中外侧线神经，以及躯干腹侧可能存在的侧线神经，最早的有颌脊椎动物可能拥有六对甚至七对侧线神经。
