THE MUSCLE RHOMBUS. 



195 



Let us suppose that the muscle from which the rhombus 

 was cut was cylindrical. The two cross -sections will 

 then form ellipses ; in the case of a regular muscle- 

 rhombus, equal ellipses. A section through the longi- 

 tudinal axes of both these ellipses will therefore give 

 an asymmetrical parallelogram with two obtuse, and 

 two acute angles (a rhomboid). Such a section is re- 

 pre3ented in the figure. In it, a b and c d correspond 

 with the longitudinal section, a c and b d the cross- 

 sections. The latter are identical with the longitudinal 

 axis of the actual cross-sections. On the side corre- 



FIG. 52. TENSIONS ON A REGULAR MUSCLE-RHOMBUS. 



spending with the longitudinal section, the greatest 

 positive tension is no longer found in the middle, but 

 is removed toward the obtuse angles, at e and e'. The 

 tensions fall very rapidly from here toward the obtuse 

 angle, gradually toward the acute angle. In the cross- 

 sections the greatest negative tension occurs near the 

 acute angles ; and the fall toward the acute angles is 

 very abrupt, that toward the obtuse angles is gradual. 



The iso-electric curves on such a regular muscle- 

 rhombus in the cross -sections form ellipses, one pole 

 of which corresponds with a focus on the edge of the 



