. The Biological bulletin. Biology; Zoology; Marine biology. Figure 3. The possible contribution to CA elongation of circumfer- ential slippage between straps and struts. (A) Outline of the ball-and- socket joint off. tribulotdes with the spine in two positions of maximum inclination. Position 2 was traced accurately from a scanning electron micrograph (ref 12), and position 1 was inferred. LF represents a large fiber at the outermost surface of the CA. When the spine moves from position 1 to position 2, this fiber elongates by ca. mm. (B) Schematic diagram of one ligament loop and its rel
. The Biological bulletin. Biology; Zoology; Marine biology. Figure 3. The possible contribution to CA elongation of circumfer- ential slippage between straps and struts. (A) Outline of the ball-and- socket joint off. tribulotdes with the spine in two positions of maximum inclination. Position 2 was traced accurately from a scanning electron micrograph (ref 12), and position 1 was inferred. LF represents a large fiber at the outermost surface of the CA. When the spine moves from position 1 to position 2, this fiber elongates by ca. mm. (B) Schematic diagram of one ligament loop and its relationship to a skeletal strut in the outermost layer of the test. During the spine inclination illustrated in (A), the large fiber swings through an angle of ca. 30°. (C) According to the new model, in a slack ligament the straps can slide over the struts (C,) (M = marker adhering to the outer surface of the strap). Assuming that the straps form inextensible loops (which is necessary to permit any calculation, but unlikely given that the rest of the fibers are extensible in the slack ligament!), fiber inclination would not change the effective length (EL) of their free arms (EL, = EL). If, as is proposed by del Castillo et in the catch state circumferential slippage is blocked (C2), inclination of the fibers would shorten one arm of the loop and lengthen the other; since displacement along the axis of the fiber is limited by the shorter arm, the eflfective length would be reduced (ELj < EL,). The contribution of circumferential slippage to fiber elongation is thus (EL, - EL2). This can be calculated for the example in (A) above. If circum- ferential slippage is blocked, an inclination of 90° would change the lengths of the free arms of the loops by the equivalent of one quarter of the circumference of the curved surface of the strut: X circumference = X X diameter = For an inclination of 30°, the change in length is therefore 0J85d + 3 =
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