On the MUSCLES. 257 



Strutted, as that their hypotenufes meafure 13 inches, their 

 bafes 12, and altitude 5 inches, and that the hypotenufes 

 reprefent two oblique irmfcles. It is plain, that when thefe have 

 fhoitened themfelves one inch, or one thirteenth part of their 

 leneth, they will move the point A through a >fpace of five 

 inches, or five times farther than flraight mufcles of the fame 

 length, Shortened in the fame proportion, could do. 



Hence, as the obliquity of an oblique mufcle is gradually 

 increaling during its action, its force is diminifhing ; while its 

 effect, of producing exteniive motion, is increaling. Thus, a 

 mufcle, reprefenting the hypotenufe of a right-angled tri- 

 angle, whofe fides ar-e 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 act, it has three- fifths 

 of the ftrength of a flraight 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 flraight 

 mufcle. 



To illuftrate what I have been demonflrating, I ufed, after 

 diffecting and demonflrating the recti mufcles of the abdomen, 

 to cut their ends off from the ofTa pubis, and to apply them to 

 the tops of the ofTa 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 

 flraight 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 intercoflal mufcles ; and after fhewing the two layers of 



Vol. III. K k thefe 



