British reptiles and batrachians . t in regular and wave-like succession,the wave as it were, started with the anterior ribs, passingdown through the entire length of the snake, and succeeded byanother and then another set, as the first movement passes on;just as you see a long streamer or a curtain-fringe moved by thewind, wave after wave following in succession, so that you canscarcely define where each undulation begins, all moving onharmoniously. When a serpent is actually progressing, everysingle pair of ribs is, of course, in action : but should only onepart of the hody be stirring, the
British reptiles and batrachians . t in regular and wave-like succession,the wave as it were, started with the anterior ribs, passingdown through the entire length of the snake, and succeeded byanother and then another set, as the first movement passes on;just as you see a long streamer or a curtain-fringe moved by thewind, wave after wave following in succession, so that you canscarcely define where each undulation begins, all moving onharmoniously. When a serpent is actually progressing, everysingle pair of ribs is, of course, in action : but should only onepart of the hody be stirring, the ribs at that part only may beactive. To each pair of ribs one of the broad under scales(ventral scutce) is attached by muscles, so that these also move 26 REPTILES AND BATRACHIANS. along in turn, like a foot, to its special pair of ribs. Just so manyvertebra as a snake has in its spinal column, so many ventralplates or scuta there are ; and by these broad under-scales youcan always ascertain how many joints there are in the spinal. Fis:. 8.—Skeleton of a snake. column. The very long snakes have three or even four hundredvertebra in their spine, smaller snakes perhaps only one hundredand fifty or two hundred. Where the tail begins the ribs ofcourse cease, but the tail bones are reckoned among the ver-tebra. As a general rule vipers have short tails; and the long, THE OPHIDIA. 27 slender, harmless snakes very long tails, tapering so gradually thatyou cannot readily decide where the tail begins. But there areexceptions. When a snake is about to cast its cuticle you willsee it pushing its jaws against the gravel in the cage or whateverrough surface may be there, and turning its head over to rub firstone side and then the other and the top. Presently the skin isloosened round the lips, and by continual rubbing and beingpushed folds back, the upper part over the head and the lowerover the throat; and when the head is free no more rubbing isnecessary, as the snake has only to crawl,
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