STRUCTURE OF THE PROBOSCIS AND RAYS OF THE STAR-NOSED MOLE, CONDYLURA-CRISTATA

The 22 anemone-like rays of the star-nosed mole, Condylura cristata, c onstitute a unique mammalian structure. These rays, 11 surrounding eac h nostril, have at least three distinct lengths and are covered on the front, back, and sides with sensory receptors or Eimer organs. The co nduit for these incoming stimuli, the infraorbital branch of the fifth cranial (trigeminal) nerve, is extremely large and composed of at lea st three distinct bundles (receiving fibers from rays 1-3, 4-7, and 8- 11). The proboscis moves on a unique nasomaxillary articulation by mea ns of highly differentiated nasolabial musculature. Elongation of the proboscis during the evolution of Condylura appears to have weakened t he masticatory mechanism. As a consequence, the procumbent central inc isors, the spatial separation among the lateral incisors and premolars , slender mandibular rami, and the fragile coronoid and angular proces ses distinguish Condylura from all other talpids but recall specialize d vermivores (among the tenrecs and civets) and termite-eaters (among the hyenas). Varied lengths of the rays, uniform distribution of the s ensory papillae containing the Eimer receptors, and proximity of the n erve endings to the surface of the stratum corneum support the hypothe sis of electrosensitivity in addition to tactile function for this ada ptive complex.