334 



ANIMAL MECHANICS. 



few reductions, the following bi-quadratic equation of condition 

 to determine the position of the axis of maximum work — 



- K(m* + i) A 4 



+ 2C (ml (ra 4 + i) - ml' (ra 4 - i)j A 3 



+ 2C (ra 2 - i) [mX (ra 4 - i) - ml' (ra 4 + i)j X 



+ (ra 2 - i) (ra 4 - i) 7T = o. 



I am now required, in order to justify my Postulate, whei. 

 applied to the complex case of skew muscles, to find the root 

 of equation (92) for various muscles, and to show that the 

 actual axis of rotation corresponds with that root. I select 

 for examination the adductor secundum of various animals. 

 This muscle, in all animals that I have dissected, forms a 

 double sheet folded at the centre on itself, in this manner : 

 the posterior fibres proceeding from the ischium are inserted 

 the highest upon the femur, and gradually increase in length 

 until we reach the most dependent point of the pubo-ischium ; 

 this portion of the muscle I shall call adductor secundus (a) ; 

 in like, but reversed order, the anterior fibres proceeding 

 from the pubes are inserted highest up on the femur, and 

 gradually increase in length until they join the long fibres of (a), 

 with which they coincide ; this portion of the muscle I shall 

 call adductor secundus (j3). Thus, the two sheets of muscle, 

 (a) and (|3), are placed side by side, as if folded against each 

 other on an axis corresponding to the longest and middle 

 fibres of the muscle ; and, although it is evident that the 

 two sheets generally may act together, yet, mechanically 

 considered, they are to be regarded as quite distinct 

 muscles. 



(1) Adductor secundus (/3) — Llama. — Having dissected 

 down upon the adductor muscles of a (ine male Llama, after 

 previously ascertaining the limits of abduction of the femur, 

 before removing the skin and gracilis muscle ; and having 



