. The Cambridge natural history. Zoology. CAUDAL FIN 237 dorsal fin of the Devonian Crospopterygian, -Holoptycliius ^ (Fig. 138), where several radialia, which are free distally, have their bases united into a single basal piece, or basipterygium. In most Teleostomi elevator and depressor muscles arise from the radialia, and are inserted into different points on the bases of the fin-rays, and by their contraction the latter may either be elevated into an erect position, or folded back like a fan along the middle line of the body, where, as in some Teleosts, there is a groove for their receptio
. The Cambridge natural history. Zoology. CAUDAL FIN 237 dorsal fin of the Devonian Crospopterygian, -Holoptycliius ^ (Fig. 138), where several radialia, which are free distally, have their bases united into a single basal piece, or basipterygium. In most Teleostomi elevator and depressor muscles arise from the radialia, and are inserted into different points on the bases of the fin-rays, and by their contraction the latter may either be elevated into an erect position, or folded back like a fan along the middle line of the body, where, as in some Teleosts, there is a groove for their reception. When fin-rays are only capable of simple eleva- tion or depression, the connexion between a radial element and its fin-ray is usually by some form of a hinge-joint, the cleft base of the ray clipping the distal segment of the radial (Fig. 139). In some Teleosts the articu- lation of the two is by means of a kind of chain- link (Fig. 137). In those Fishes in which the median. fins are capable of lateral Fig. end of the yertehral column of ^ ^ , J ji A TtovX (Salmo fario). CN, Centrum ; , dermal fin-rays ; , haemal spine ; , haemal zygapophysis ; , neural spine ; , neural zygapophysis ; UST, the up- tilted, partly ossified, and unsegmented ter- minal portion of the iiotochord, or urostyle. (From Parlcer and Haswell.) undulatory movements the articulation is of a more mobile character. In the different types of caudal fin, diphycercal, heterocercal, and homocercal, the supporting elements of the ventral lobe are formed by the haemal spines of the terminal caudal vertebrae which are inclined backwards, and are often greatly expanded for the purpose (Fig. 140). The dorsal lobe may be supported either by the adjacent neural spines, or by radialia, or by both. The Appendicular Skeleton.^—It is probable that the skeleton of the paired fins and the pectoral and pelvic girdles have been formed from the supporting radialia of the isolated and enlarg
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
