190 PHYSIOLOGY OF MUSCLES AND NERVES. 



parallel to each other, and that the two cuts are made 

 at right angles to the direction of the fibres. Fig. 49 

 diagrammatically represents a regular muscle-prism of 

 this sort. The horizontal stripes represent the separate 

 bundles of the fibres. The outer surface of the prism, 

 which therefore corresponds with the upper surface of 

 the fibres, is called the loiujitudiiial section of the 

 prism ; and the terminal surfiices, at right angles to 

 the longitudinal section, are the cross-sections of the 

 muscle-prism. The lines running at right angles to 

 the direction of the fibres are, as we shall presently 

 find, tension-curves. 



A regular muscle-prism such as this exhibits a very 



n, a' a/ n' a' a n.' a' a' a' a' 



Fig 49. A regilau mlscle-prism, 



simple distribution of tension. All the lines of tension, 

 or the iso-electric curves, run on the surface and are 

 parallel to the cross-sections. Ivound the middle of the 

 muscle-prism passes a line separating it into two sym- 

 metrical halves ; this we will call the equator. The 

 greatest 'positive tension to be found anywhere on the 

 surface prevails at this point. Every point on the 

 equator has a greater positive tension than any other 

 point on the longitudinal, or the cross-section. On 

 either side from the equator, the positive tension gra- 

 dually decreases along the longitudinal section quite 

 regularly in both directions, until, at the point where 

 the longitudinal meets the cross-section, it = 0. 



On the cross-sections themselves the tension is 



