ANIMAL MECHANICS. 



329 



Hence we have 



ab = 2.76, cd = 22.61 

 ab + cd = 32.37 

 ef<= 31.24- 



This result is sufficient to show that, in Man, the Pectinceus 

 muscle is nearly inscribable in a circle. 



3. Llama. — In the Llama, I obtained the following : — 



Pectinceus Muscle {Llama). 



I. 



Length of origin, .... 



1. 91 in. 



= a. 



2. 



Length of insertion, . . . 



• 3-50 ti 



= b. 



3- 



Length of anterior fibres, 



• 3-°5 » 



= c. 



.4- 



Length of posterior fibres, . 



. 6.91 „ 



= d. 



5- 



Length of first diagonal, . . 



. 4.09 „ 



= e. 



6. 



Length of second diagonal, . 



• 6.77 „ 



-/• 



Hence, we find 



ab = 6.68, cd = 2 1.07 

 ab + cd ■= 27.75 

 ef = 27.69. 



It appears, to my mind, impossible to evade the conclusion, 

 that the particular form of muscle employed in the preceding 

 cases, was the result of design and foresight ; for the chances, 

 a priori, would be many millions to one against the occurrence 

 of the particular quadrilateral which can be inscribed in a 

 circle, if the formation of the muscle depended on slow ran- 

 dom variations of external conditions, only. 



I shall now proceed to consider the general case of a skew 

 muscle, formed by fibres arranged in any manner joining two 

 bones, AB, and A'B', not lying in the same plane. Let Z4, 

 and I' A' be the directions in which the bones AB and A'B 1 are 

 placed ; / and 1' being the points corresponding to II', which 



