STRUCTURE OF MUSCLES. LZ 
ces from the joints. The positions assigned them are not al- 
ways the most favourable for the movement of the levers ; 
but they could not be otherwise, without altering the external 
shape, and giving to it an appearance the very reverse of those 
round or tapering forms so commonly exhibited in organiz- 
ed bodies. But the disadvantages attending the obliquity 
of the muscles, with respect to the bones which they are 
destined to move, are abundantly compensated by other 
means. ‘lhe heads of the bones are frequently larger than 
the body to which the tendons are attached ; so that these, 
by passing over the convexity to the place of their insertion, 
form a more obtuse angle with the lever, than if the head 
did not exist. The origi and insertion of a muscle are 
frequently at some distance ; and the muscie passes through 
holes in other bones, or is bound down by annular liga- 
ments ; so that the motion is performed without destroying 
the proportion of the part. Although muscles, which thus 
move the bones as so many levers, may be compared. to 
ropes in the effects which are produced, there is a remark- 
able difference in the manner of their action. As the 
muscles contract in length in every part, and, by the con- 
traction, change their shape and become more rigid and an- 
gular, every bundle may be said to assist another ; so that 
in the very muscle itself, there may be formed both levers 
and fulera; thus giving to it powers, which, were it acting 
like a cord, it could not have in consequence of its posi- 
ton. 
Let us now take a view of the muscles, as concerned in 
the production of the different motions exhibited by ani- 
mals. These are exceedingly various in their extent and 
duration, and in the organs employed to perform them. 
It is obyious, that as animals are exposed to the vicissi- 
tudes of the elements, the fluctuation of the atmosphere and 
