464 



BIRD. 



in the sternal apparatus, both of those which have 

 the one habit and those which have the other, ac- 

 cording as they combine it more or less with the 

 action of the wings, yet there are characters descrip- 

 tive of each, that run through the whole. 



Sterna of the anisodactyli. Some of these use the 

 wings more and some less, but as they are all more 

 or less walkers on the boles of trees, and other sur- 

 faces, on which, from their form, and especially from 

 their position, there can be but little stability arising 

 from the ordinary pressure of gravitation, which is 

 the principal means of stability upon horizontal sur- 

 faces, they require to be birds of very ready wing, 

 which can instantly throw themselves upon that part 

 of their organisation, in the event of their claws miss- 

 ing hold. The wing required for this purpose must 

 have muscles of considerable power, and also firm 

 feathers. Such wings have to be used in all positions 

 of the body ; sometimes both, and at other times only 

 one of them can act, and they often strike against 

 trees, branches, and other hard substances, so that 

 they require more strength in their whole structure, 

 than wings which are used only in the free air. 



Some of these birds also feed on the wing, and 

 feed on the sweet juice of blossoms, to acquire which 

 there must be much use of the wing before even a 

 little bird can procure a meal. Thus, though the 

 wings of these birds cannot be considered as the 

 most general or immediate of their organs in feeding, 

 they are very essential in some, and in all they are 

 auxiliaries which need to be constantly in readiness. 

 As the wings, even of those species which use them 

 the most in feeding, are not used for long stretches, 

 but merely for flitting about from flower to flower, 

 they all have the character of twitching wings, which 

 take the air by sudden jerks more than of wings 

 of forward flight ; but notwithstanding this undulating 

 style of flight, some of them get through the air with 

 much rapidity. We shall select as specimens for 

 illustrating the sternal apparatus of the tribe, one of 

 the humming-birds of the tropical parts of America, 

 which is a feeder on the wing, and the common 

 hoopoe, which is a summer migrant in the warmer 

 parts of Europe, and feeds on the ground or on trees. 



Humming Bird. 



The sternal apparatus of these very small birds is, 

 as may be seen by the figure, remarkably well deve- 

 loped, though, like that of the swallow tribe, it com- 

 bines not a little of the character of a carrying basket 

 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 

 principle, it must follow that the shorter the fibre is 

 the sooner must it be wholly brought into action, and 

 the sooner also must its individual effort be over. 

 All muscular action (as the reader must of course be 

 aware) consists in a contracting or shortening of the 

 fibres, and a proportional increase in thickness. How 

 the shortening takes place is a part of the subject 

 upon which it would not be very wise to offer any 

 conjecture, as it is one upon which we possess no 

 knowledge ; but the action itself can be observed, and 

 we may rationally conclude that the times in w hich 

 equal degrees of excitement are communicated to 

 muscles are in proportion to the lengths of their 

 fibres : that one-half of the length will be brought into 

 action in half the time, and so of all other proportions. 

 This will hold true, whatever may be the absolute 

 :engih of the time, even though it should be, as it no 

 doubt is in the case of very minute muscles, too 

 short for our being able to measure, or in any way 

 estimate its length in terms of any other motion. But 

 as the shorter muscle must act in the shortest time, so 

 action of the longer one must be greater, if the 

 requisite time is allowed it it must contract more, or 

 capable of moving the same weight over a greater 

 space. 



From the indeterminate quantities, which we have 

 no means of separating, or even of expressing, that, 

 as already noticed, enter into the very complex ope- 

 ration of muscular action, what has been now stated 

 can be regarded only as a glimmer in the dark, yet 

 t is far from being without its use, especially in *oe 

 comparison of structures so varied in their actions, 

 yet all formed on the same general principle, as the 

 wings of birds. 



A short muscle will, from what has been said, per- 

 brm its extent of motion more rapidly than a long 

 one ; but it will not move so heavy a member, or 

 move it over the same effective extent at one contrac- 

 tion. Hence we find that birds which rush upon their 

 Key on the wing, have the sternum broader at those 

 larts to which the grand and middle pectoral, which 



