122 m. straus-durckheim's 



In general, they augment in thickness a little before their 

 insertion ; but as, notwithstanding their solidity, they require 

 to be moveable upon the piece ';hjy put in motion, the larger 

 ones offer, near their extremity, a small flexible narrowed por- 

 tion, resembling an articulation. They are generally simple at 

 their extremity, but sometimes bifurcate, as the flexor iibice in 

 the genus Limulus. 



M r cles. 



The muscles of insects, and in general of all the Annulusa 

 and Annelida, differ from those of Vertebrata, in being of a 

 less firm consistence. Indeed, they are sometimes in a gela- 

 tinous and almost transparent state ; and it is only by being 

 steeped in alcohol, or some other liquid/ that they acquire a 

 sufficient degree of opacity and firmness to enable us to distin- 

 guish their form; yet their power surpasses that of the muscles 

 of larger animals. 



They are composed of a multitude of fibres, in which the 

 power of contraction resides, and which are mostly straight, 

 and separate one from another, but are sometimes united in 

 bundles which rarely are connected. 



The fibres are composed of small, nearly triangular plates, 

 placed obliquely one upon another. These plates are nearly 

 flat; but one of the sides is produced so as to form an angular 

 fold in the middle of the plate, which gradually diminishes 

 until it ceases, just before reaching the opposite margin. 



In the Vertebrata the muscles often have a tendinous origin, 

 or offer a tendinous portion in the middle (as the digastricus, 

 &c. in man). This is very rarely the case in the articulated 

 animals. 



The solid cupules, to which the extremities of some muscles 

 are attached, appear to be the analogues of the aponeuroses b of 

 Vertebrata ; they are generally found at the origin of the long 

 tendons, but sometimes both ends of a muscle are furnished 

 with them. 



a I have always found alcohol, mixed with a small portion of acetic acid, the 

 best mixture forgiving firmness to the internal parts of insects. They should, 

 however, be well washed with pure alcohol afterwards, or the acid will ruin the 

 knives or scissors used in dissecting. — E. D. 



b Aponeuroses are the expanded parts of the tendons which cover the muscles, 

 give insertion to their fibres, strengthen their action, and restrain them in their 

 proper places. — E. D. 



