ARRANGEMENT OF STRUCTURAL ELEMENTS. 



21 



fibres of different sizes having the similar physiological 

 functions. 



I have made the attempt to determine whether the 

 number of nerve fibres going to the segment of the frog's 

 leg above the knee as compared with the number going 

 to the segments below the knee bore any relation to the 

 mass of muscle and area of skin belonging to these 

 divisions, and also whether the nerve fibres were of 

 different diameters according to their destination. The 

 frog (Rana catesbiand] which was used weighed 13 '5 

 grammes, the muscles of the entire leg weighed 1*9 

 grammes, of which 1*3 grammes represented those above . 

 the knee, and '6 those below, a ratio of 2'i6-i. The 

 total area of the skin on the leg was 21*3 sq. cm., being 

 6*5 sq. cm. above, and 14*8 sq. cm. below, the knee, a 

 ratio of i-2'2, or almost exactly the reverse of that 

 found for the weight of muscle. If the area of the 

 cross-section of the nerve trunk were proportional to the 

 weight of muscle and area of skin taken together, it 

 might be expected that it would be nearly the same for 

 the two portions of the limb. The following table ex- 

 hibits the relations observed : 



TABLE 52. SHOWING IN A FROG OF 13-5 GRAMMES THE AREA 

 OF THE PORTION OF THE NERVE TRUNK, THE NUMBER OF 

 FIBRES, AND THE AVERAGE AREA OF THE FIBRES, DISTRI- 

 BUTED IN THE ONE CASE ABOVE THE KNEE, AND IN THE 

 OTHER, BELOW IT. ALSO THE RELATIVE WEIGHTS OF THE 

 MUSCLE MASSES AND THE RELATIVE AREAS OF SKIN IN 

 THESE Two PORTIONS OF THE LEG. 



