MUSCULAR ACTION. 345 



with that of an organ upon which to establish the 

 means of powerful flight. It has a considerable re- 

 semblance to the sternum of the swift, being long in 

 proportion to its breadth, and considerably broader in 

 the rear than toward the front. In general it is 

 without notches or holes at the posterior angles. 

 The keel is perhaps more developed in proportion to 

 the size of the whole bone than in any other bird ; 

 the coracoids are also short and strong ; and the sca- 

 pulars, from the particular way in which they are 

 bent, take a firm hold in their embedment. The 

 form of the furcal bone is also good, though not a 

 perfect arch; but it is proportionally weaker than 

 the other parts of the arrangement. 



We may glean something respecting the highly 

 interesting but exceedingly obscure subject of muscu- 

 lar action, from the study of this sternum. It is 

 higher in the keel in proportion than any other, and 

 the height is continued farther backward than in most 

 birds ; but the anterior part, where the great muscles 

 of flight are attached, is narrow, narrower in propor- 

 tion to the height of the keel than in any other known 

 species. Hence, though the muscles admit of a 

 greater number of fasciculi of fibres than if the rela- 

 tive breadths of the side of the sternum and the keel 

 had been different, yet these fibres must be propor- 

 tionally shorter. 



Now, though muscular action is not capable of 

 being estimated with mathematical accuracy, because 

 we have no measure of any action of the living prin- 

 ciple, and the very same muscle is capable of many 

 different degrees of action, arising from health, ex- 

 citement, and various other circumstances which can- 

 not be reduced to a numerical scale ; yet as the action 

 is mechanical in its effects, whatever it may be in its 



