FIN SPINES 29 
position was probably in the median line of the body. 
The well-marked, backward curve of the spine suggests _ 
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Figs. 32-38. — Fin spines. 32. Fin spine and pectoral fin of Acanthodian. 
33. Hybodus (cestraciont shark). 34. Sting-ray, Zrygon. 35. Edestus heinrichsii 
(Carboniferous shark, known only from its spine), side view of spine. X }. 36, 
37, 38. Dorsal view, separated element and transverse section of Edestus spine. 
that fin structures could not well have existed behind it. 
Each separate element has an elongated basal portion, 
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