The principal objective of this study is to quantitate the basic neural-receptor cell interrelationships in the vestibular sensory regions of the shovel-nosed guitarfish and the bullfrog to establish the neuro-anatomical framework within which the functional operation of the system may be interpreted. This objective will be accomplished by: a) neuronal mapping techniques on a light microscopic level, b) a morphometric analysis of synaptic relationships at an electron microscopic level, and c) a systematic tracing of structural components directly on electron micrographs from consecutive serial sections. The specific aims of the project are: 1) to ascertain the number and distribution of nerve fibers to, and within, the sensory regions of the cristae; 2) to determine the variation in synaptic arrangements in different regions of the cristae; 3) to discover the number, relative positions and types of hair cells in synaptic contact with individual nerves; 4) to study the interrelationships between the afferent-efferent complex; 5) to determine the patterns of selective degeneration following transection of the VIIIth nerve and ultimately to establish the incidence of nerve regeneration together with patterns of synaptic reinnervation; and 6) to correlate the anatomical findings to the functional operation of the cristae thereby serving as a basis for collaborative physiological testing predicated upon a fuller understanding of the anatomical input to the system.