. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. MOTION. 435 «ffect of the stroke. In the back stroke, the thigh (d, fig. 229) moves first, describing an arc of a circle about their iliac extremity, from d to d' and d" successively. During this move- ment the legs e and tarsi _/" are flexed pas- sively, and carried forwards to e',J~', so as to act with little effect on the water. The two thighs d" d" begin to approach their greatest flexion forwards, the legs ef c' and the phalanges f J'" extend in succession, so that the water opposes resistan
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. MOTION. 435 «ffect of the stroke. In the back stroke, the thigh (d, fig. 229) moves first, describing an arc of a circle about their iliac extremity, from d to d' and d" successively. During this move- ment the legs e and tarsi _/" are flexed pas- sively, and carried forwards to e',J~', so as to act with little effect on the water. The two thighs d" d" begin to approach their greatest flexion forwards, the legs ef c' and the phalanges f J'" extend in succession, so that the water opposes resistance to only one of them at a time. The tarsi (_/") having been completely extended outwards, the two legs are suddenly carried backwards, pressing on the water, with the entire plane of the tarsi, and as the silky fringes which cover the phalanges are extended at the same instant, their surface is considerably augmented. The other parts of the two legs press- ing upon the tarsi, as in the walk or the leap, projects the body forward in the direction of its axis. In walking, the two members of the same pair act alternately, in order to serve, each in its turn, as a support to the centre of gravity. In swimming, on the contrary, the body being supported by the water, the two members move simultaneously, in order to give the greater impulse, and it is in this respect that swimming differs essentially from walking, and more nearly approaches leaping. The middle legs of the Dytiscus act in a manner similar to the posterior, but being shorter and weaker, contribute little towards accele- rating the movements of the animal; the an- terior pair appear to be used chiefly for the purpose of altering the direction of its motion. The motions of insects in the water may be thus explained : let a b (Jig. 230,) be the axis of the body passing through the centre of gravity o ; and let c o be the excess of the specific gra- vity of the water over that of the insect, acting in a vertical di
Size: 1629px × 1533px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, booksubjectanatomy, booksubjectphysiology, booksubjectzoology
