Tongue evolution in lungless salamanders, family plethodontidae. III. Patterns of peripheral innervation

Abstract

Innervation of the tongue and associated musculature in plethodontid salamanders was studied using Palmgren stained sectioned materials, fresh dissection, and whole mounts of experimental specimens treated with horseradish peroxidase (HRP). Species studied were chosen to represent modes of tongue projection recognized by Lombard and Wake ('77). Special attention was given to species of the genera Plethodon, Batrachoseps, Pseudoeurycea, and Hydromantes, but representatives of other genera were investigated. As expected we found that cranial nerves IX and X and spinal nerve 1 supplied the muscles involved in tongue movement. The peripheral courses of the nerves were traced, and both functionally related and phylogenetically determined routes were found. As relative projection length increases, the nerves supplying the tongue tip also increase in length. When the tongue is at rest the long nerves are stored in coils. The coil of ramus lingualis lies between the ceratobranchials, but that of ramus hypoglossus is more variable, although constant within a species. Ramus hypoglossus bifurcates into separate branches to tongue and anterior musculature of the floor of the mouth. In generalized, presumably primitive, modes the bifurcation and coiling are far anterior. In most of the tongue projection modes bifurcation is relatively posterior, but in one, bifurcation is anterior, but coiling is relatively posterior in position. The most unusual condition is in Hydromantes, in which bifurcation is relatively posterior and a coiled ramus hypoglossus joins a coiled ramus lingualis to form a unique, coiled common ramus to the tongue tip. Hydromantes has the greatest projection distance of any salamander.

Three‐dimensional reconstruction of the cranial and anterior spinal nerves in early tadpoles of Xenopus laevis (Pipidae, Anura)

“…A contribution of the first two spinal nerves to the hypoglossal nerve has been reported for many urodeles (Coghill, 1902;Norris, 1913;Wake, Roth, & Wake, 1983) and caecilians (Wake, 1992(Wake, , 1993. This fits with the report of two motor nuclei within the spinal cord.…”

“…Like in D. pictus , we found that the first two, maybe even three, spinal nerves contribute fibers to the formation of the hypoglossal nerve. A contribution of the first two spinal nerves to the hypoglossal nerve has been reported for many urodeles (Coghill, ; Norris, ; Wake, Roth, & Wake, ) and caecilians (Wake, ). This fits with the report of two motor nuclei within the spinal cord.…”

Frog tongue acts as muscle-powered adhesive tape

“…The evolution of a muscular tongue has been a major innovation of terrestrial vertebrates [1,2] and is directly related to the emergence of a wide variety of feeding modes on land [3]. Especially, the projectile tongues of chameleons [4][5][6][7][8][9], several salamander species [10][11][12][13][14][15] and many species of frogs [16][17][18][19][20][21] have received considerable attention because of their ability to reach distant prey items at high velocities. Tongue adhesion generally is a highly dynamic process, and the time spent for contact formation between the tongue and the target is in the range of only a few milliseconds [7,11,17,22].…”

The strike of the tiger salamander: quantitative electromyography and muscle function during prey capture

“…Tongue projection is the salient feature of terrestrial prey capture in salamanders (Duellman and Trueb 1986;Lauder and Reilly (in press); Wake 1976, 1977;Regal 1966;Reilly and Lauder 1989b;Severtsov 1972;Wake 1982;Wake et al 1983). Reilly and Lauder (1989b) presented a kinetic model for tongue projection in Ambystoma tigrinum based on kinematics and the observed lines of action of individual muscle pairs and combinations of muscles (but not on recordings of muscle activity patterns).…”