MUSCULAR POWEII. 121 



displacement, and have impeded their co-operation 

 in one common eft'ect. Nature has guarded against 

 this evil by collecting a certain number of the 

 elementary fibrils, and tying them together with 

 threads of cellular substance, thus forming them 

 into a larger fibre ; and again packing a number 

 of these fibres into larger bundles: always sur- 

 rounding each packet with a web of cellular tissue; 

 which thus forms a separate investment for each. 

 This plan of successive reunion into larger and 

 larger assemblages is carried on through several 

 gradations of size, till the entire muscle is com- 

 pleted. 



That we may be the better able to appreciate the 

 excellence of the plans adopted in the mechanism 

 of the animal frame, let us inquire what arrange- 

 ments would occur to us, prior to an acquaintance 

 with those actually adopted, as the njost advan- 

 tageous dispositions of the muscular power. It is 

 evident, that the simplest mode would be that of 

 extending the fibres of the muscle in a straight 

 line between the points intended to be brought 

 nearer to each other. This direct application of 

 the power, however, is seldom compatible with 

 convenience, unless the parts to be moved are of 

 very small size, and require very delicate adjust- 

 ments. Straight muscles, accordingly, are cm- 

 ployed chiefly for the movements of the minuter 

 parts of the apparatus belonging to the senses, such 

 as the eye, and the ear, and also that of the voice. 

 In insects, when the hard case, or skeleton, is 

 wholly external, this direct application of the 

 moving force is also very generally employed. 

 The shells of the bivalve Mollusca, as of the Oyster 



