Oa the MUSCLES. 257 
ftructed, as that their hypotenufes meafure 13 inches, their 
bafes 12, and altitude 5 inches, and that the hypotenufes 
reprefent two oblique nmufcles. It is plain, that when thefe have 
fhortened themfelves one inch, or one thirteenth part of their 
length, they will move the point A through a dpace of five 
inches, or five times farther than ftraight mufcles of the fame 
length, fhortened in the fame proportion, could do. 
Hence, as the obliquity of an oblique mufcle is gradually 
increafing during its action, its force is diminifhing ; while its 
effet, of producing extenfive motion, is increaling. Thus, a 
mufcle, reprefenting the hypotenufe of a right-angled tri- 
angle, whofe fides are to each other as the numbers 3, 4 and 5, 
and the altitude 3, by fhortening itfelf half an inch, does not 
move its infertion one full inch; but if it is fhortened another 
half inch, its infertion ‘is moved through a fpace of upwards 
- of two inches more. When it begins to at, it has three-fifths 
of the ftrength of a ftraight mufcle of the fame fize; but when 
it acts again, after having moved its infertion the fpace of 
an inch, it has two-fifths only of the ftrength of the ftraight 
mufcle. 
To illuftrate what I have been demonftrating, I ufed, after 
diffeQing and demonftrating the recti mufcles of the abdomen, 
to cut their ends off from the ofla pubis, and to apply them to 
the tops of the offa ilia, fo as to reprefent oblique mufcles; and 
from this I was led to'make the remark, that if both the two 
external oblique, or the two internal oblique mufcles, or all 
thefe, acted at once, the obliquity of the one balancing the 
obliquity of the other, the trunk of the body would be bended 
ftraight forwards, and that flexion made by them might be 
greater than that made by the recti mufcles, which, at firft 
fight feemed to be more fuited to the purpofe. 
In like manner, I ufed to take out feveral of the ribs, with 
their intercoftal mufcles ; and after fhewing the two. layers of 
Vou. LI. Keke re? thefe 
