THE HUMMING BIRDS. 



291 



the nape and along the throat allow the neck to readily lie against the middle of the 

 back, or to bend downward over the point of the breastbone, while the bare spaces 

 under the wing and along the sides of the body permit the wings to be easily closed 

 and applied to the body, the side spaces conforming almost exactly to the curve of the 

 edge of the folded wing. The large bare space on the under side, found in nearly all 



Fig. 1. — The above illustration shows the dorsal and ventral aspects of the pterylosis of a Humming 

 Bird (Florisuga mellivora). A small triangular space on the crown of the head is not seen. (Natural 

 size.) 



birds save water-fowl, is mainly to allow the warmth of the body to be directly ap- 

 plied to the eggs during incubation, and in birds like ducks and penguins, which are 

 densely or completely feathered beneath, a bare spot is present during the breeding 

 season. 



Skeleton. — The most obvious features in the skeleton of a Humming Bird are the 

 width of the front portion of the skull, long neck, short wing, and, above all, dispro- 

 portionately large breastbone. 



The arrangement of the bones of the palate is of the kind termed schizognathous,* 

 and, while the skull in general shows but little to indicate relationship with other 

 groups of birds, the base of the cranium is very Swiftlike and the palate and frontal 

 region have some slight leanings toward the Woodpeckers. 



The length of the neck may be best appreciated by saying that in Humming Birds 

 the neck forms four-sevenths of the vertebral column, while among Swallows it forms 

 but three-sevenths, the number of vertebrse being the same — fourteen — in each case. 



Following the neck vertebrse are three free dorsal vertebra; and these are succeeded 

 by a " sacrum" of twelve fused vertebras, the vertebral column being terminated by 

 six caudals. 



There are eight pairs of ribs, this being an unusually large number among birds, 

 and especially among land birds, where the ordinary number is six pairs. The first 

 three pairs of ribs join the three free dorsals, the succeeding four pairs are attached 



*The description here given of the skeleton is based on Trochilus cohibris, and while 

 this species agrees in all save very minute points with other species examined, it is 

 to be expected that when more is known of the osteology of the Trochilidse skeletal 

 differences will be found to exist in the group. 



