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, constitute a unique mammalian structure. These rays, 11 surrounding each nostril, have at least three distinct lengths and are covered on the front, back, and sides with sensory receptors or Eimer organs. The conduit for these incoming stimuli, the infraorbital branch of the fifth cranial (trigeminal) nerve, is extremely large and composed of at least three distinct bundles (receiving fibers from rays 1-3, 4-7, and 8-11). The proboscis moves on a unique nasomaxillary articulation by means of highly differentiated nasolabial musculature. Elongation of the proboscis during the evolution of Condylura appears to have weakened the masticatory mechanism. As a consequence, the procumbent central incisors, the spatial separation among the lateral incisors and premolars, slender mandibular rami, and the fragile coronoid and angular processes distinguish Condylura from all other talpids but recall specialized vermivores (among the tenrecs and civets) and termite-eaters (among the hyenas). Varied lengths of the rays, uniform distribution of the sensory papillae containing the Eimer receptors, and proximity of the nerve endings to the surface of the stratum corneum support the hypothesis of electrosensitivity in addition to tactile function for this adaptive complex.