254 OBSERVATIONS 
Tuus, let PA and DE (T. 2. fig. 4.) be two parallel lines, 
and let AB and AC reprefent two ftraight mufcles, and 
AD and AE two oblique mufcles, it is plain, that when the 
two ftraight mufcles have fhortened themfelves one third part 
of their length, their infertion A will be brought down to num- 
ber 1. But when the oblique mufcles A D and AE, by acting 
together, have brought the point A down to 1, and are in the 
fituation of the dotted lines 1D and 1E, they cannot have loft 
more of their length than the length of the perpendicular Ar, 
which is fhorter than the hypotenufe AJ, or lefs than the third 
of the length of the oblique mufcle. In fac, they have loft 
lefs of their length than At, becaufe the two fides Ar and 1E 
of the triangle A1E muft be longer than the third fide AE; 
and therefore oblique mufcles can perform as great a degree of 
motion as ftraight mufcles, without being fhortened in the fame 
proportion; or, which is the fame thing, if they continue to 
act till they are fhortened in the fame proportion, the place of 
their infertion, A, will defcend farther, or through a larger 
{pace. 
I sHALL now proceed a ftep farther, and endeavour to de- 
monftrate, that where two oblique mufcles balance each other, 
the motion of their infertion is more extenfive than can be pro- 
duced by two ftraight mufcles of the fame length with the 
oblique mufcles. : 
Tuus, in T.2. fig. 5. let AB and AC reprefent two ftraight 
mufcles, and AD and AE two oblique mufcles of the fame 
length, and we fhall fuppofe the length of each mufcle to jcon- 
fit of any given number of inches or parts, fuppofe five parts, 
1, 2, 3, &c. or I, II, III, &c. and when in action to be capa- 
ble of fhortening itfelf one fifth part or two fifth parts of its 
length. Let the two correfponding numbers 1 and I, or 2 and 
II, be joined by the ftraight lines 1 I, and 2 II, fo as to form 
the ifofceles triangles Art I, or A 21. When the two ftraight 
mu({cles 
