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 superificial neuromasts, but superficial neuromasts have longer kino-cilia 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.

Gars, like most other ray-finned fishes, possess lines of superficial and canal neuromasts that form highly ordered spatial arrays on the head and trunk. These neuromasts are innervated by three pairs of cranial nerves: anterior, middle and posterior lateral-line nerves. Application of horseradish peroxidase to the roots of these nerves indicates that the afferent fibers of each nerve terminate throughout the rostrocaudal extent of the ipsilateral octavolateralis column, composed of medial and caudal octavolateralis nuclei, as well as rostrally in the eminentia granularis of the cerebellum. The afferents of each nerve terminate within different regions of these nuclei, thus preserving a rostrocaudal somatotopy of the peripheral receptors. The individual rami of these nerves innervate peripheral receptors in a dorsoventral sequence; however, application of horseradish peroxidase to these rami indicates an almost total overlap of the terminal fields of adjacent rami and, thus, little or no preservation of dorsoventral somatotopy of the peripheral receptors. Similarly, the terminal fields of fibers that innervate canal and superficial neuromasts overlap extensively, and there is no evidence for separate maps of canal and superficial neuromasts. Furthermore, the position of the terminal fields of superficial neuromasts is not consistent with a hypothesis that these receptors may have evolved into electroreceptors in some teleosts. However, these experiments do indicate that superficial neuromasts, like canal neuromasts, are innervated by efferent fibers of rostral and caudal efferent nuclei, but there is no evidence of a diencephalic efferent nucleus as occurs in teleosts.