228 THE MUSCLES. 



age, sex, and state of health ; but on taking a general average, it will be found 

 that it represents nearly one-half the entire weight of the body. 



B. Situation. — There is no need to insist upon the fact, that a knowledge 

 of the situation of the muscles is one of the firet objects to be acquired with 

 regard to their arrangement. 



They may, like the bones, be described in two ways. 



1. In relation to the median plane of the body ; whence their division into 

 pairs and single muscles. The last, very few in number, are far from exhibiting 

 the symmetry which exists in the bones of the same order, as may be seen in the 

 diaphragm. 



2. In relation to the other organs ; such as the bones and surrounding 

 muscles. 



C. FoEM. — With regard to their absolute form, the muscles, again, like the 

 bones, are classed as long, wide, and short. 



Long muscles. — These muscles are more particularly met with in the limbs. 

 Provided with a principal axis, to which we may ascribe the effect of their 

 contraction, they present a middle portion — usually thick, and tivo extremities of 

 unequal thickness ; the most voluminous, always turned upwards, is metaphori- 

 cally designated the head, the other the tail. They are most frequently /i<s?/o/7«, 

 sometimes conical, but rarely cijlindrical, prismatic, ov flattened into thin bands. 



Thus, as Bichat remarked a long time ago, there are muscles which have no 

 other analogy with the long muscles of the limbs than in their external appear- 

 ance. These are the long muscles lying above or below the spine, and which are 

 composed of a series of fasciculi indistinguishable at their origin and distinct at 

 their termination ; or fasciculi, each of which has a distinct origin or termination 

 on the vertebrfe. 



Wide muscles. — Wide muscles are those which have two principal axes, and 

 are stretched beneath the skin, or around the great cavities of the trunk, which 

 they concur in enclosing and separating from one another. They are ellipticaly 

 quadrilateral, triangidar, trapezoid, etc. 



Short muscles. — These are found chiefly around the short bones, or at the 

 periphery of the articulations which are deeply buried under enormous muscular 

 masses. Although their name indicates that their three axes offer nearly the 

 same dimensions, yet there is most frequently one, and even two, which pre- 

 dominate. They may therefore be assimilated, in this respect, to the long or 

 wide muscles. 



D. Direction. — Cruveilhier has justly remarked, that the direction of a 

 muscle is one of the most important features in its history ; for it allows the 

 determination of the angle of incidence of the muscle on its arm of the lever, its 

 power, and its uses. 



With regard to the direction of muscles, we may observe : 1. The form of 

 their principal axis. 2. The relation of this axis to the vertical line. 3. Its 

 comparison with the axis of the bony levers which the muscles surround or moves. 



a. A muscle is termed rectilinear when its principal axis is straight ; it is 

 curvilinear, or circular, if this axis describes a curve more or less marked ; it 

 becomes inflected when it proceeds in a certain direction, and afterwards turns 

 on a bony or cartilaginous pulley in another direction — that is to say, when its 

 principal axis is broken into several lines. If the muscle offers two axes, it will 

 \)Qflat or concave, these being one or the other, or straight or curvilinear. 



J. With regard to the direction of the muscles to that of the plumb-line, it 



