. Guide leaflet. h were stiffenedinternally by rod-like skeletal supports, and externally by spines formedin the skin. All the fins functioned as keels and rudders rather than aspaddles. Between the pectoral and the pelvic fins in certain primitive fishesthere were several other pairs of fins. Evidently the paired fins were similarboth in origin and in construction to the median or unpaired fins. The fins in ancient and modern sharks were supported bv skeletal rodswhich were laid down in the membranes between adjacent muscle seg-ments. The anal, pelvic and pectoral fins of early fossil sharks
. Guide leaflet. h were stiffenedinternally by rod-like skeletal supports, and externally by spines formedin the skin. All the fins functioned as keels and rudders rather than aspaddles. Between the pectoral and the pelvic fins in certain primitive fishesthere were several other pairs of fins. Evidently the paired fins were similarboth in origin and in construction to the median or unpaired fins. The fins in ancient and modern sharks were supported bv skeletal rodswhich were laid down in the membranes between adjacent muscle seg-ments. The anal, pelvic and pectoral fins of early fossil sharks (Fig. 10) exhibitprogressive stages in the squeezing together of the basal rods into a U-shaped girdle. The subsequent historv of the shoulder girdle from fish to man is sum-marized in Figs. 11-13. In typical fish the pectoral girdle consisted of: (i) anouter or dermal series of bony plates (including the cleithra, clavicles, etc.)and (2) an inner or primary shoulder girdle, including the scapula andcoracoid. [30.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectnatural, bookyear1901
