202 



ANATOMY OF VERTEBRATES. 



130 



on resuming its length ; but it is commonly drawn out straight, as 

 before the contraction, by ( antagonistic ' muscles, in the living 



animal. The uncontracted state of mus- 

 cular fibre is sometimes termed ' relaxa- 

 tion,' but is more properly a state of 

 quiescence or equipollency. 



Muscles consist of series or bundles of 

 the elementary fibres, with their vessels 

 and nerves, connected together by areolar 

 tissue : either in lengthened or flattened 

 masses, fixed at the two extremities, called 

 f solid muscles ; ' or disposed around cavities 

 or canals, and called ' hollow muscles.' 



The non-contractile fibrous parts by 

 which the ' solid muscles ' are attached to 

 the endo- sclero- and exo-skeletons, are 

 called ' tendons ' when long and slender, and 

 s aponeuroses ' when broad and flat. 

 46. Myology of Fishes.- The modification of the active organs 

 of motion, and their deviation from the fundamental vertebrate 

 type, proceed concomitantly with the metamorphosis of the passive 

 organs, as Vertebrates rise in the scale and gain higher and more 

 varied endowments : therefore, as the segments of the skeleton 



131 



Stages of contraction seen in an 

 elementary fibre of the Skate. The 

 uppermost state is that previous to 

 the commencement of contraction. 



CLXXXV. 



Muscular system, Perca fluviutills 



preserve the greatest amount of uniformity in the lowest class, so 

 does the principle of vegetative repetition most prevail in the 

 corresponding segments of the muscular system. 



The chief masses of this system in ordinary Osseous Fishes are 

 disposed on each side of the trunk, in a series of vertical flakes or 



