72 PTERYLOGRAPHY. 



CHAPTER II. 

 SINGING-BIRDS (Passerinai). 



THE pterylographic variation in this large group, which includes two fifths of all the known 

 birds, is less than in either the preceding or the following groups, so that this portion of their 

 organization confirms the observation deduced by me from all the characters of the Singing-birds, 

 that, when taken in their correct and most natural limits, they form the most constant and uniform 

 group to be found among birds, and that we must, therefore, proceed most cautiously in 

 employing the few differences which they present for the purpose of grouping the species in 

 natural genera, subgenera, and families. 1 The following pterylographic characters are general 

 and deserving of notice. 



The contour-feathers usually have a very weak and downy aftershaft, 2 but they have no 

 down-feathers among them, except in one genus (Cinclus). Down-feathers are also in most cases 

 entirely deficient on the spaces, or they are very much scattered upon them. The number of 

 contour-feathers is very small, although, perhaps, not the least that occurs among birds. They 

 form, without exception, limited narrow tracts, and leave the greater part of the trunk uncovered. 

 The number of these tracts is as usual, but the proportions of the spinal and inferior tracts are 

 alone characteristic. The head is usually clothed with an uninterrupted plumage, in which, 

 however, there is immediately behind the eye a small, naked, roundish spot, concealed by the 

 contour-feathers, to which I give the name of the temporal space (see antca, p. 36, and Plate III). 

 This space is, however, often wanting for example, in Tanagra, Pardalotus, and others. Two 

 main tracts issue from the head one on the nape, as the commencement of the spinal tract ; the 

 other from the densely feathered throat, as the commencement of the inferior tract. The spinal 

 tract always forms a linear or band-like stripe, is never interrupted between the shoulders, and is 

 dilated only upon the back behind the scapulae into a rhomboidal or elliptical saddle, which, in 

 many cases, incloses an oval or fissure-like space, the ephippial space (apfcrium scllce}. Behind the 

 saddle the rump-land commences, frequently, when a space is present, with two convergent single 

 or double rows of contour-feathers (see Plate III, fig. 15), but becoming again a simple, although 

 rather broader stem at the caudal pit and ceasing at the oil-gland. The two rows of feathers 

 behind the saddle appear to be very rarely wanting, as, for example, in Hirundo (Plate III, fig. 14). 

 The inferior tract is divided before the middle of the neck into two symmetrical halves, each of 

 which is continued along the middle of the breast, and terminates in front of the anus. The 

 two halves are widely separated from each other ; they emit no true lateral branch upon the 

 breast, but are much dilated throughout this entire region ; and it is only at the end of this dilated 



1 Upon the general organization of this group see the article " Passerinse," in ' Ersch und 

 Gruber's Encyklopadie,' iii sect., Bd. xiii, p. 139, which was worked up from an Essay by Nitzsch. B. 



2 I have not always been able to detect it, and must therefore suppose that it is sometimes 

 wanting, e. g, in Ocypterm and Eurylaimus. 



