THE CURRENT OF M. GASTROCNEMIUS. 199 



was laid bare. Such cross-sections may be termed 

 artificial, while the longitudinal sections of these prisms 

 or rhombi may be called natural. Longitudinal sections 

 may also be formed artificially, by splitting the muscle 

 in the direction of its fibres ; and we may speak of 

 natural cross-sections, by which we understand the 

 natural ends of the muscle-fibres while still closed with 

 the tendonous substance. Now the action both of longi- 

 tudinal and of cross-sections is the same whether they 

 are natural or artificial. 1 It is, therefore, always pos- 

 sible to obtain currents from an uninjured muscle 

 exactly as from artificially prepared muscle-prisms and 

 rhombi. 



5. To the circumstance that it can, while still un- 

 injured, afford powerful currents, is due the special 

 importance of the gastrocnemius. This muscle may 

 in all essential points be classed among the penniform 

 muscles ; though in reality it is thus conditioned only 

 towards its upper tendon, the part toward the lower 

 tendon being rather of the character of a semipenniform 

 muscle. In order to understand its structure, let us 

 imagine two tendonous plates, an upper and a lower, 

 connected by muscle-fibres stretched obliquely between 

 them, so as to form a semipenniform muscle. Now let 

 us suppose the upper tendonous plate to be folded in the 

 middle, as a sheet of paper might be, and that the two 

 folded halves are in apposition. We now have an 

 upper tendon plate, situated within the muscle, from 

 which muscle-fibres pass obliquely in both directions ; 

 the lower tendon has, however, been so bent by the 

 folding of the upper so that the whole muscle is shaped 

 like a turnip split in a longitudinal direction, the flat 

 1 Exceptions to this rule will presently be mentioned. 



