342 



ANIMAL MECHANICS. 



Let I A and T A' represent the directions of the bones 

 AB and A'B\ and let II be the shortest line joining these 

 directions. Through the point I draw IX parallel to IA ; 

 then the axis IX represents equations (102). 



It follows from this construction, that if the Postulate 

 (p. 238) be true, the socket S / of the hip joint must lie some- 

 where on IX, the axis of maximum instability. 



The following measurements were made on the pelvis and 

 femur of the Llama. Draw from the centre of the acetabulum, 

 S, two perpendiculars, SK and SK\ upon the line of pubic 

 origin and femoral insertion of the adductor secundus (j3) ; the 

 lengths of these perpendiculars and of the line 81 were then 

 measured, as follows : — 



SI 



= p = 3.21 in. 



SK 



= p = 2.77 „ 



SK' 



= p' = 1.02 „ 



If it be true that the point S lies on the axis IX (since 

 II = 2c, and A' IX = 2</>), we must have, within the limits of 

 errors of observation, 



p = 2C, 



. = sin 26. ( I0 3) 



Introducing the measured values, we obtain 



p = 2.77 in. 

 2^= S°° 58'. 



These values differ from the constants of the hyperboloid — 

 2c by 0.39 of an inch, 

 20 „ i°43'. 



These differences are within the limits of errors of observation, 

 and we may consider the Postulate to be proved true, when 

 applied to the skew adductor of the Llama. 



