138 



VISION 



1 cm 



Figure 13 Dorsal view of the brain of a sphyrnid shark, Sphyrna tiburo (the bonnethead 

 shark), alll, anterior lateral-line lobe; alln, anterior lateral-line nerve; en, central nucleus; 

 lob, lateral division of the olfactory bulb; lp, lateral pallium; mob, medial division of the 

 olfactory bulb; oe, olfactory epithelium (organ); ot, optic tectum; p, deep ophthalmic or 

 profundus nerve; pill, posterior lateral-line lobe; plln, posterior lateral-line nerve; II, optic 

 nerve; III, oculomotor nerve; V, trigeminal nerve; VII, facial nerve; VIII, statoacoustic 

 nerve; IX, glossopharyngeal nerve; X, vagal nerve. 



determined an overall elasmobranch coefficient of allometry (ot) of 0.76, 

 with a coefficient of determination (r ) of 0.86. The coefficient of allometry 

 for the sharks in this sample is 0.75 (r = 0.96), whereas the coefficient for 

 the skates and rays is even higher (a = 1.04; r = 0.67). Similar elasmobranch 

 data were reported by Bauchot et al. (1976). These workers reported an 

 elasmobranch coefficient of 0.939 but did not calculate separate coefficients 

 for sharks and rays.* Using the data listed in their Table 1, I calculated a 

 shark coefficient of 0.73 (r 2 = 0.78), and a skate and ray coefficient of 1.38 

 (r 2 = 0.83). These figures agree closely with my own data, and together they 

 indicate that the batoids possess iso- or positive allometry, a condition rarely 



*An error by Bauchot et al. was incorrectly indicated in Northcutt 1977b, a result of mis- 

 interpretation in personal communication and failure to realize differences in the respec- 

 tive statistical methods employed. 



