FIN SPINES 



29 



position was probably in the median line of the body. 

 The well-marked, backward curve of the spine suggests 



Figs. 32-38. — Fin spines. 32. Fin spine and pectoral fin of Acanthodian. 

 33. Hybodus (cestraciont shark). 34. Sting-ray, Trygon. 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, 



