252 1NSECTA. 



Such is the comparative strength of insects. Let us now pro- 

 ceed to examine the muscles to which it is owing their structure 

 and general arrangement. 



(293.) The muscles consist of bundles of delicate fibres, that 

 arise either from the inner surface of the segments composing the 

 skeleton, or else from the internal septa ( 281.) which project into 

 the thorax. The fibres themselves are of a white or yellow colour ; 

 and so loosely are they connected by cellular tissue, that they may 

 be separated by the slightest touch. 



All the muscles of an insect may be arranged in two great 

 divisions; the first including those that unite the different seg- 

 ments of the body ; the second, those appropriated to the move- 

 ments of the limbs, jaws, and other appendages : the former are 

 entirely composed of fleshy fibres ; the latter are provided with 

 tendinous insertions, by which their force is concentrated and made 

 to act with precision upon a given point of the skeleton. 



The connecting muscles are generally arranged in broad parallel 

 bands, arising from the inner surface of a given segment, and 

 passing on to be inserted in a similar manner into another seg- 

 ment, so that by their contraction the cavity in which they are 

 lodged is diminished by the approximation of the different rings : 

 these have no tendons. 



The locomotive muscles of course take their character from the 

 joints of the limb upon which they act ; and, as we have already 

 seen that these movements are generally confined to those of a 

 hinge, the muscular fasciculi may be conveniently grouped into 

 two great classes, the flexor muscles, that bend the joint ; and 

 the extensors, by which it is again straightened, and brought back 

 to its former position. This simple arrangement will be best 

 understood by an inspection of the appended figure (fig. Ill), 

 representing the muscles of the leg of a cockchafer (Melolontha 

 vulgaris), as they are depicted by Strauss Durckheim.* In the 

 thigh, for example, there are two muscles, one of which bends, 

 the other straightens, the tibia. The flexor (fig. Ill, a) arises 

 from the lining m'embrane of the femur, and is inserted by a ten- 

 don into a process of the tibia in such a manner as to flex the 

 leg upon the thigh ; while its antagonist (&), attached to a process 

 derived from the other side of the joint, has an opposite effect, and 

 by its contraction extends the leg. In the tibia there are like- 



* Considerations ge"ne"rales sur 1'Anat. comp. des Animaux Articules, auxquelles on 

 a joint 1' Anatomic descriptive du Hanneton. 1 vol. 4to. Paris, 1828. 



