ANIMAL MECHANICS. 



229 



above the point of the linea alba under consideration. The 

 value of>, at the navel, is 4.25 in. (p. 221), and it increases 

 as we go downwards towards the pubes, where it becomes 

 8. 1 1 inches. While, therefore, the horizontal component of 

 the external oblique is everywhere the same, its vertical com- 

 ponent reaches a maximum just above the pubes. 

 This maximum is represented by 



8.1 1 x o.2C x 2 COS 7C C 



2 =2-2_ = 0.614 



5.4I 



The vertical and transverse strains produced by the inter- 

 nal oblique, are both variable, as shown by equations (40) 

 and (41) — 



Tr 2/'versin20 



V = 



w 



H = t sin 2 <£. 



Ie these equations, /, 0, and <p are all variable, and in the fol- 

 lowing manner : — Let the point be taken on the linea alba 

 (about half way between the navel and the pubes), where the 

 fibres of the muscle become horizontal. At this point there is 

 no vertical strain, and the horizontal strain is a maximum, be- 

 cause <f> becomes a right angle ; the transverse strain at other 

 points varies as the square of sin 0, but is always less than at 

 the point named. With respect to the vertical strain at any 

 point, it is thus found : 2O = 90 0 - 0 is the angle made with 

 the horizontal line, by the fibres passing towards the point, 

 and / varies, as the base of the triangular muscle formed by 

 these fibres and the horizontal fibres. Now, it is evident that 

 the versine of 20 and the base of the triangular muscle both 

 increase as we pass along the linea alba, in either direction, 

 above or below the central point between the navel and pubes. 

 where the whole action of the internal oblique is transverse ; 

 sc that the vertical strain produced by this muscle has two 

 maxima., one near the pubes, and the other near the ster- 



