292 REPORT OF NATIONAL MUSEUM, 1890. 



to the first four vertebrae of the '' sacral " series, while the eighth and last pair is 

 entirely free at the upper end. The last ribs almost meet the long, slender, down- 

 curved pubic portion of the pelvis, securely hooping in the viscera and giving an un- 

 usual air of strength to the skeleton. 



The bones supporting the tail are provided with long recurved processes to furnish 

 ample attachment for the well-developed caudal muscles, for the tail forms an im- 

 portant adjunct to the wings when the Humming Bird hangs poised in the air, extract- 

 ing the honey from some flower. 



The shortness of the wing is due to the shortened humerus, radius, and ulna, the 

 remainder of the wing bones being rather long. 



The coracoid, the bone to which the wing is hinged, has a very peculiar form among 

 Humming Birds. In the large majority of birds, the tendon running from the muscles 

 that raise the wing plays in a notch in the upper end of the coracoid, but in the 

 Humming Bird this notch is bridged over and the tendon plays securely through the 

 perforation thus formed. 



Fig. 2. — The above, figure of the shoulder-girdle and attached portion of the skeleton of a Humming 

 Bird (Selasphorus platyccrcus) , seen from below, shows the coracoid with its perforations, and the ex- 

 tremely long bones of the hand, the figure being twice the natural size. 



The legs seem small, but in reality are proportionately larger than in many other 

 birds, the sharp, curved claws in particular being decidedly well developed. 



Skeletal affinities. — In the number of ribs the Humming Birds are approached, but 

 not equaled, by some Swifts, both groups agreeing in the incomplete character of the 

 last pair when more than six pairs are present in any Swift. 



The wing of the Humming Bird is largely unique in character and in minor points 

 is intermediate between the Swifts and Passeres. 



The manner in which the coracoid joins the sternum — by a shallow cup-and-ball 

 joint — is peculiar to Swifts and Hummers. 



In the character of the sternum and the manner in which the ribs are attached to 

 its sides the two groups are nearly alike, while the posterior limbs of both agree in 

 many particulars. 



Generalizations. — Skeletal modifications are of two kinds, technically termed mor- 

 phological and physiological, the former depending on the relationships of the animal 

 the latter on its habits. 



In order to better understand the skeleton of the Humming Bird, the form of the 

 feathered wing and mode of its flight should continually be borne in mind, for the 

 Humming Bird is emphatically a bird of the air, and all its parts are modified accord- 

 ingly. 



The external wing is characterized by the great development of the primaries and 

 almost complete functional suppression of the secondaries, while the wing beats are 

 frequent and all movements of the bird sudden. Just how rapid the wing beats are 

 must for the present be merely a matter of conjecture, but it can be said that the 



