78 Clark, Pterylosis of Swifts and Hummingbirds. LJan 



being characteristic of the Trochili. The upper cervical tract is 

 completely united on each side of the neck with the lower cervical 

 for a considerable distance, so that there is a distinct lateral cer- 

 vical tract for some little distance on the side of the neck, which 

 ultimately divides to form the real cervicals. The conspicuous 

 and characteristic nuchal apterium occupies the upper surface 

 of the greater part of the neck. The humeral tracts are well 

 defined, rather short, pass over the upper end of the humerus, 

 and at their posterior end are usually very slightly connected by 

 2 or 3 feathers with the dorsal tract. The latter is very broad, 

 covering most of the back, but contains a long and conspicuous 

 spinal apterium. Posteriorly it unites more or less completely 

 with the femoral tracts, though the latter are usually quite easily 

 distinguished, as the feathers composing them are larger and stouter 

 than those which connect them with the dorsal. The lower cer- 

 vical tract is divided as far forward as the angle of the mouth, 

 into two branches, which for a part of their length are united with 

 the upper cervical, as already described. Each half passes back- 

 ward, over the sides of the breast, as the sternal tract, which is 

 wide and well developed; they terminate so abruptly just poste- 

 rior to the margin of the sternum that there are practically no 

 ventral tracts. Anteriorly the sternal tracts are connected over 

 the shoulders with the feathering on the upper side of the wings 

 and thus with the humerals. 



The characteristic and important features of this pterylosis. 

 may be summarized as follows: the presence of frontal and supra- 

 ocular apteria, a very large and conspicuous nuchal apterium, and 

 a long and conspicuous spinal apterium, the absence of lateral 

 cervical apteria, the small femorals noticeably connected with the 

 dorsal, the well-marked sternals and practical absence of ventrals. 

 In addition to these features, the following points are worthy of 

 note. Aftershafts are present on the contour feathers though 

 very weak. True down feathers are wanting and filoplumes are 

 not notably abundant except on the neck and to a lesser extent on 

 the back. The oil gland never bears a terminal tuft of feathers. 

 There are always 10 rectrices and 10 primaries; of the latter, the 

 tenth is the longest, the others successively shorter. The alula 

 is usually wanting, though a single feather is sometimes present 



