MOVEMENTS OF THP] WINGS OF BIRDS. 



229 



of each of which it is difficult to discover. There is therefore 

 some limit to the precision of the measurements which we can 

 take by the electric method ; we can still, however, estimate 

 by this means the duration of a movement with a tolerably 

 accurate approximation. 



Myographic method. — We have seen that a dilatation accom- 

 panies the contraction of the muscles, and follows it through 

 all its phases. A shortening of the muscle, either rapid or 

 slow, feeble or energetic, as the case, may be, will therefore be 

 accompanied by a lateral dilatation which will have similar 

 characters of rapidity or intensity. At each depression of the 

 wing of a bird, the large pectoral muscles will be subject to a 

 dilatation which it will be necessary to transmit to the re- 

 gistering apparatus. 



We shall have recourse, for this purpose, to the apparatus 

 which we have employed in determinations of the same kind, 

 when treating of human locomotion. Some slight modifica- 

 tions will enable them to give signals of the alternate phases 

 of dilatation and relaxation of the large pectoral muscle. 



Fig 93. — Apparatus to investigate the contraction of the thoracic muscles 

 of the bird. The upper convex surface is formed ot a membrane of india- 

 rubber supported by a spiral spring ; this part is applied to the muscles. 

 The lower surface, in contact with the corset, carries four small hooks 

 which are fastened in the stuff and keep the instrument in its place. 



The bird flies in a space fifteen metres square and eight 

 metres high. The registering apparatus being placed in the 

 centre of the room where the experiment is made, twelve 

 metres of india-rubber tubing are sufficient to establish a 

 constant communication between the bird and the apparatus. 



A sort of corset is fixed on a pigeon (see figure 94). Under 

 this corset, between the stuff, which is tightly stretched, and 



