452 GENERAL ANATOMY. 



tract, if their attachments are fixed; and, in tending to bcrome 

 so, they diminish the cavities of which they form the walk: 

 as is the case with the abdominal muscles and diaphragm with 

 respect to the abdomen; and they enlarge the cavity to which 

 they correspond by their convex surface; as the diaphragm 

 does with respect to the thorax. The reflected muscles, and 

 they are very numerous, tend, like the curved muscles, to 

 become straight during their contraction; but if any insur- 

 mountable obstacle comes in the way, the motion, the direc- 

 tion of which is changed, is transmitted to the one or the other 

 extremity, or to both, according to their mobility. 



728. When one of the parts to which a muscle is attached, 

 is immoveable, the other capable of being moved, it draws 

 the latter towards the former; as is the case with the muscles 

 which extend from the bones to the soft parts, &c. When one 

 of the two parts has little mobility, and the other is very mo- 

 bile, as the trunk with reference to the limbs, the central ex- 

 tremity of the limbs with reference to the peripheric extremi- 

 ty, &c. the latter is in general the only one that moves. But 

 it is to be observed, then, in this case, that the fixed point, and 

 the moveable point of the muscles may change. Thus, in 

 the most ordinary motions of the arm, the muscles which 

 move that part have their fixed point in the trunk, and their 

 moveable point in the limb. On the contrary, in the action 

 of climbing up a tree, the fixed point, at the moment when 

 the trunk rises towards the arm which was previously fixed, 

 is in the arm, and the moveable point in the trunk. So also 

 in the action of going up a ladder, when the leg is carried 

 forwards and upwards, the fixed point is in the trunk. When 

 afterwards the trunk rises towards the leg whose foot is sta- 

 tionary and firm, the fixed point is in the leg, and the move- 

 able points of the muscles are in the thigh and trunk. 



When the two parts to which the muscles are attached are 

 nearly equally mobile, contraction tends to move them about 

 equally. Thus when one is lying upon a horizontal plane, 

 the contraction of the anterior muscles of the trunk tends 

 nearly equally to bend the head upon the neck, and the pelvis 

 upon the loins. 



