186 



ANIMAL MECHANICS. 



mean of 0.48 in. The length of the line XYZ was 7.42 in., 

 and that of xyz, 4.27 in.* Hence we find the following : — 



Pectoral Muscle of Heron. 



Section. 



Length. 



Thickness. 



Area. 



XYZ, . . . 

 xyz, . . . 



7.42 inches. 

 4.27 



0.258 inches. 

 0.48 „ 



i. 914 sq. in. 

 2.049 » 



This result shows that the cross 

 section of the muscle is constant ; 

 but, in order to verify the result, 

 I cut out two templets in zinc, of 

 exactly the shape of the cross sec- 

 tions in Fig. 32, and weighed 

 them, with the following re- 

 sult : — 



Weight of (a) = 63.4 grs. 

 Weight of (b) = 65.6 „ 



When we consider the difficulty 

 of measuring exactly the cross 

 section of a muscle, the foregoing 

 results must be regarded as prov- 

 ing that its cross section is, prac- Fig J2 

 tically, constant. 



Among the advantages that arise from this arrangement 

 of fibres in complex muscles, one of the most obvious is the 

 equal strength which it gives to all parts of the muscle, which 

 would not be secured by any web-like arrangement, allowing 



* The total weight of the muscle was 2.68 oz. av. 



