359-299 million years ago
Early amphibians evolved a number of novel characteristics of the nervous system which are shared among modern tetrapods. These include a larger brain with additional nuclei, a better olfactory system with a separate vomeronasal system, hair cells to perceive sound, and new types of receptors for general senses.
Ancestral amphibians evolved reticular regions in the midbrain shared
with amniotes and the optic tectum expanded to cover the tori semicirculares
(Ariens, p. 1196). Afferent fibers lead to the optic tectum, even in blind
amphibians (Ariens, p. 1196). In the diencephalon, the dorsal thalamus
increased in size, increased connections were made between the dorsal
thalamus and the telencephalon, olfactory pathways connected the diencephalon
to the telencephalon, such as the stria terminalis (Ariens, p. 1197) the
nucleus ventrolateralis was divided into a dorsal and ventral regions
(Butler, 1996, p. 262), and a lateral hypothalamic nucleus evolved (Butler,
1996, p. 336).
Amphibians increased the ability of their skin to perceive sensations with the evolution of Pacinian corpuscles (Ariens, p.186) and the first proprioceptors (Romer, p. 498). Amphibians incorporated hair cells in the perception of sound (Romer, p. 532) and an auditory ossicle involved in hearing (the stapes) (Romer, p.532). The papilla basilaris may represent a primitive homolog of the organ of Corti in amniotes (Kardong, p. 684). Vision was enhanced with the evolution of moveable eyelids, lacrimal glands, and lacrimal ducts.