They are, in their conformation, analogous to the form of the limb, which they in part determine, and which they especially maintain, by preventing the displacement of the subjacent parts, a displacement which would continually take place, from the laxity of the cutaneous organ. Their thickness varies. In general, the greater the number of the muscles they cover, the greater their thickness; hence why the aponeurosis of the fascia lata is superior in this respect to the brachial; why that of the fore-arm is thicker in front than behind; why the plantar and palmar are so considerable, whilst hardly any fibres are found on the back part of the foot and the hand. There are however some exceptions to this rule; for example, the aponeurotic covering of the posterior part of the leg is not in proportion to the power of the gastrocnemii and solæus muscles; thus these muscles are more than all the others exposed to displacements, frequently very painful, which constitute cramp, and which it is necessary to distinguish from the pains or numbness which result from the compression of one of the nerves of the lower limbs, as of the sciatic, or the external plantar, a compression produced by a bad position, or any other analogous cause. Externally, the aponeuroses of the general covering are contiguous to the integuments. A very loose texture unites them, so that the latter can easily slide over them in external pressures. Immoveable between these motions and those of the muscles, they entirely separate them; so that the skin and the muscles that correspond to it, have not, in this respect, any influence upon each other. Within, these aponeuroses are in general loosely joined to the muscles by cellular texture. Here and there they send between the different muscular layers numerous elongations, which are afterwards attached to the bone, and which, at the same time that they furnish points of attachment, increase the solidity of the covering of the limb. _Tensor Muscles._ The aponeuroses for general covering have almost all one or two particular muscles that are inserted in them in whole or in part, and which are destined to give them a degree of tension or relaxation proportioned to the state of the limb. This arrangement is remarkable in the insertion, 1st, of the great dorsal and pectoral muscles in the brachial aponeurosis; 2d, of the biceps in that of the fore-arm; 3d, of the palmaris longus in the palmar; 4th, of the glutæus maximus and of the fascia lata in the aponeuroses of that name; 5th, of the semi-tendinosus, semi-membranosus and biceps in the tibial.