The laws and mechanics of circulation, with the principle involved in animal movement . neously, it must pull the revertedend of the tongue forward upon a line corresponding withthe insertion of the muscle in the mandible, or straighten itsimply, and, of course, holding it in this position during theperiod of contraction, which is all this action in the musclecan possibly do, but which only puts the organ in a positionto be suddenly projected from the mouth,. which requireselongation in both muscles in order to effect it; otherwise isutterly impossible, as must appear obvious. The special elec
The laws and mechanics of circulation, with the principle involved in animal movement . neously, it must pull the revertedend of the tongue forward upon a line corresponding withthe insertion of the muscle in the mandible, or straighten itsimply, and, of course, holding it in this position during theperiod of contraction, which is all this action in the musclecan possibly do, but which only puts the organ in a positionto be suddenly projected from the mouth,. which requireselongation in both muscles in order to effect it; otherwise isutterly impossible, as must appear obvious. The special elec-trical current for producing expansion is determined into theparts under the volition of the animal, similar to what occurs inthe electrical organ of fishes, the principle being the same, pro-jecting and retracting the organ with the rapidity of lightningby reason of this action of the electrical current; otherwiseis inexplicable. Fortunately, however, we have a means ofstudying the action in the muscles ready to our hand, inwhich the movements are more slowly performed, but 462 DUALISM DEMONSTRATED. is equally conclusive of dualism in muscles and nervous force,notably in the tortoise, to which attention is now the Movements in the Head, Neck and Tall of the Tortoise, with Reference to the Principle in Musculation. Dualism in muscles and nervous force has striking illustrationin the muscular actions for producing the movements in thehead, neck and tail of the tortoise ; but in order to place thematter fully before the student, it will be necessary to makebrief reference to the special anatomy in the parts or the bonesand muscles concerned in the movements, beginning with thecervical vertebrae. Cervical Vertebrae.—In chelonia the cervical vertebrae areelongated, eight in all, the last one (Fig. 191, 8), articulatingwith the first dorsal, is short and broad, with the anteriorsurface of the body divided into two transversely elongatedconvexities, the
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