42 



muscular membrane extended between the bases of its feet, by 

 which it is enabled to swim ; but what is curious about it is, that 

 it swims backwards by impelling the water forwards. 



CHAPTER VI. 



ON THE MUSCULAR SYSTEM IN THE VERTEBRATA. 

 PISCES. 



In all the vertebrata the soft parts are uniformly placed external 

 to the hard resisting textures : in them the muscles of animal life 

 are generally of a red colour, and connected to bone by at least one 

 extremity, through means of tendinous or fibrous structure. In 

 fishes, the muscular fibres are soft, gelatinous, and colourless as in 

 the in vertebrata, and the embryos of the higher vertebrated classes. 

 In the salmon, however, they are of a higher red, especially about 

 the head ; and in the lamprey they are blackish gray. The 

 arrangement of the muscles in the osseous fishes is such, that a 

 large mass extends from head to tail on each side, divided by fibrous 

 bands into numerous strata. The active movements of fishes are 

 not subject to much variety ; their ascent or descent is effected 

 by the compression or expansion of the air-bladder, and by their 

 pectoral fins, whilst they are impelled forwards by the lateral motion 

 of the tail opposed by the resistance of the water. When the 

 swimming bladder is absent, as in the sole genus, or very small, as 

 in the cobitis fossilis, the animal either remains at the bottom, or 

 swims on one side by the vertical motions of the tail. The remora, 

 lump-sucker, and others are provided with a muscular disk in the 

 form of a sucker, by which they adhere to other fish or bodies 

 moving through the water: so powerful is the muscular tail of the 

 salmon, that, aided by the great elasticity of its spine, it is able to 

 mount over cataracts fifteen feet high. The shark is especially 

 remarkable for speed, so much so, that according to a calculation of 

 Sir E. Home, it would, if not compelled to rest, swim over the cir- 

 cumference of the globe in thirty weeks. 



AMPHIBIA. 



The proteus, siren, and the tadpoles of the higher anurous spe- 

 cies, are moved through the water by the same kind of lateral 

 motion of the spine and tail as in fishes. The oreat lateral mus- 

 cles that accomplish these motions are still pale, bloodless, and 

 feeble, and their connecting cellular tissue is soft, scanty, and 

 colourless; the muscles are slightly connected to the skin, and pre- 

 sent but little appearance of tendinous structure. So far the mus- 

 cular system closely resembles that of fishes, but in the adult state 



