410 



MECHANICAL AND ACOUSTICAL SENSES 



Another highly intriguing feature of hearing in sharks concerns those areas 

 in the labyrinth that supply the information necessary for their demonstrated 

 sensitivities and orienting abilities. Lowenstein and Roberts' (1951) study of 

 the ear of the skate, Raja clauata, was for many years the only electrophysi- 

 ological study of the elasmo branch labyrinth. Their findings demonstrated 

 that low-frequency vibrations were adequate to elicit propagated discharges 

 from the anterior portion of the saccular macula, a portion of the utricular 

 macula (lacinia utriculi), and the macula neglecta. Vilstrup (1951), using 

 lesion techniques, found acoustical sensitivity, however, only in the pars 

 inferior of the spiny dogfish, Squalus acanthias. This was the state of the 

 knowledge until only recently, when the macula neglecta, a little-known 

 structure near the dorso-posterior aspect of the sacculus (Figure 5) came under 

 study by Tester et al. (1972) and Fay et al. (1974). Because of its relative 

 position and its high sensitivity to frequencies within the hearing range of 

 sharks, it probably does detect sound. Electrophysiological experiments by 

 Fay et al. (1974) on the blacktip reef shark, C. melanopterus, showed 

 that the largest microphonic responses obtained from the macula neglecta 



Figure 5 Schematic section of portions of the ear of the blacktip reef 

 shark, Carcharhinus melanopterus. C. Cupula; CH, chondocranium; ED, 

 endolymphatic duct; EP, endolymphatic pore; FO, fenestra ovalis; MN, 

 macula neglecta; PCD, posterior canal duct; PVC, posterior vertical canal; 

 PF, parietal fossa; RN, ramus neglectus nerve; S, sacculus; SK, skin covering 

 fossa. (Fay et al. 1974) 



