250 ANATOMY. 



attached. From the centre of this plate a longer or shorter straight 

 process springs, which unites itself with the part requiring motion. 

 The great muscles of the winajs are formed in this manner. Audouin 



o * 



considers these horny tendons as processes of the thorax, and he calls 

 them Epid ernes. 



Double-bellied muscles, or such, namely, where two bellies lie behind 

 each other, and are united together by a central tendon, as they are 

 found in the superior animals, are not discoverable in insects. 



Besides this division of the muscles, according to their variations of 

 form, we may likewise separate them into three groups, according to 

 their functions. 



The first, which we will call connecting muscles, pass within the 

 cavity of a part from one portion of the skeleton to the other, and thus 

 consolidate the connexion of the several plates together. These are in 

 general the largest of all the muscles, and they have no tendons : when 

 they contract, the cavity in which they are found contracts likewise, 

 but when they become flaccid, it again distends. To these belong the 

 large muscles of the back, which are spread between the phragmata, 

 and likewise the large muscles of the sides, which pass from the back 

 to the breast, and then those which lie between the plates of the 

 abdomen. 



The others, which may be called distinctively the muscles of motion, 

 pass from a portion of the horny skeleton to the limbs, or from one 

 joint of the latter to the other. They originate with a broad base from 

 a part of the skeleton, and pass on by a thinner apex, terminating in a 

 tendon, to a part of the limb. Their character also divides them into 

 two groups. The first, which are called FLEXORS (adductores sen 

 jlexores), lie on the inside of the limb, and draw it to its base, to 

 which it is affixed ; the others, or EXTENSORS ( abductores seu 

 exlensores), work in an opposite direction, distending the limb again 

 as soon as they get in action. They lie on the exterior of the limb, 

 and attach themselves to the exterior angle or edge of the parts to be 

 moved. 



These are the various general qualities of the muscles ; we come now 

 to the investigation of the individual ones, which we will examine in 

 the order of their situation, examining first the muscles of the head 

 and its joints,, then those of the thorax and the limbs attached to it, and 

 lastly those of the abdomen. 



