. Echinoderms of Connecticut . TS--XS FIG. 10. Diagram of transverse section of arm of an ophiuran. C, branch of coelom; L, lateral arm plate; M, muscular attachment of vertebra; N, radial nerve; S, arm spines; T, tentacle; T S, tentacle scales; U, upper arm plate; UN, under arm plate; V, vertebra; W, radial canal of water-vascular system. (Modified from MacBride.) Each vertebra, in all our native species, articulates with its neighbor by a ball-and-socket joint, the concavity on the proximal side interlocking with a corresponding projection on the distal side of its neighbor. The vertebrae ar
. Echinoderms of Connecticut . TS--XS FIG. 10. Diagram of transverse section of arm of an ophiuran. C, branch of coelom; L, lateral arm plate; M, muscular attachment of vertebra; N, radial nerve; S, arm spines; T, tentacle; T S, tentacle scales; U, upper arm plate; UN, under arm plate; V, vertebra; W, radial canal of water-vascular system. (Modified from MacBride.) Each vertebra, in all our native species, articulates with its neighbor by a ball-and-socket joint, the concavity on the proximal side interlocking with a corresponding projection on the distal side of its neighbor. The vertebrae are joined to each other by four strong muscles (Fig. 10), attached symmetrically to their faces. The contrac- tion of the two upper muscles of a series of segments bends the arm upward; a similar contraction of the lateral or lower pair bends the arm sidewise or towards the oral surface as the case may be. By suitable combinations of such muscular contractions the arms can be moved rapidly and bent about in all possible directions, with the one exception that they are so articulated that they cannot be coiled in a spiral above the disk. On the aboral side of each vertebra (Fig. 10) is a shallow groove which contains the slender extension of the body cavity,
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Keywords: ., bookcentury1900, bookdecade1910, bookpublisherhartf, bookyear1912
