Rev. S. Haughton on Animal Mechanics. 



297 



If this estimate of the cross section of the muscles be as- 

 sumed instead of my own, the coefficient found by me should be 

 increased in the proportion of 3190 to 2174 ; or 



Coefficient of muscles of forearm . . 94-7 X §159= 122 lbs. 



2171 



The mean of the coefficients found from my own measurement 

 of the muscles of the arm, and that of Professor Donders, is 

 108-1 lbs., which agrees nearly with that obtained from the 

 muscles of the leg, viz. llO'llbs., and the mean of all the ob- 

 servations on arm and leg would be 109*4 Ibs., a result which I 

 consider to be not far from the truth. 



The cross sections of the muscles were found by cutting them 

 across with a sharp scalpel, and marking out their section on 

 cardboard, and afterwards weighing the marked portions, the 

 weights of which were then compared with the weight of a 

 known number of square inches of the same cardboard, and so 

 the cross sections in square inches calculated. 



I give here, for the purpose of illustration, the actual sections 

 of the muscles of the leg. (Figs. 1-6.) 



The perpendiculars let fall upon the directions of the muscles 

 were measured by stretching strings from the origin to the in- 

 sertion of the muscles, aud measuring, by means of a compass, 

 the perpendiculars let fall upon these strings from the axis of the 

 joint. 



The weights of the muscles themselves were as follows : — 



ii. The principle of economy of force or of material in nature 

 would lead necessarily to the principle that each tendon convey- 

 ing the effect of a force to a distant point shoidd have the exact 

 strength requii'ed, and neither more nor less ; for, according to 

 the doctrine oijlnal causes, it was originally contrived by a per- 

 fect architect, and according to Lamarckian views it must have 

 perfectly accommodated itself to the uses to which it is applied. 

 According, therefore, to either view, if the tendon be too strong, 

 it will become atrophied down to the proper limit ; and if too weak, 

 it must either break or be nourished up to the requisite degree 

 of strength. It seemed to me desirable to prove this fundamental 

 proposition in animal mechanics by direct observation ; and I 

 selected for tliis purpose the tendons in the leg of several of the 

 large running birds (^Struthionidce}, — and always with the same 

 residt, viz. that the cross sections of any two muscles tending to 

 produce a similar effect are directly proportional to the cross 

 sections of their tendons. 



I shall select as an example tlie case of the flexor hallucis lonyiis 

 and flexor digitorwn communis perforans of the Khea, whose 



Ann. ^ Mag. N. Hist. Ser. 3. Vol. xx. 20 



