OF THE HUMERAL AND LUMBAR TRACTS. 25 



stunted dorsal bands, which are united only at the tail. This form occurs in Ardea (Plate VIII, 

 fig. 11) and Cancroma (Plate VIII, fig. 14), and a similar structure in Otis tetrax ; but Otis 

 tarda differs from it in having the neck-tracts connected on the throat, and the dorsal portion of 

 the spinal tract broader, with a narrower median space (Plate VIII, figs. 1 and 2). 



II. THE HUMERAL TRACT (Pterylct humeralis). 



This is one of the double tracts ; a pair of such tracts occurring in all birds. In its design, 

 it constitutes an extremely narrow band which springs from the middle of the shoulder, a little in 

 front of the shoulder joint, immediately from the margin of the great wing-membrane, and is 

 continued obliquely upon the humerus in a direction parallel to that of the shoulder blades. 

 Anteriorly, it not unfrequently coalesces with the portion of the inferior tract which approaches 

 most closely to the shoulder, or with the plumage of the great wing-membrane ; elsewhere, it is 

 completely circumscribed by spaces, being separated from the spinal tract by the lateral space of 

 the trunk, and from the plumage of the fore-arm by the upper wing-space. It varies some- 

 what in position, however, being removed in some birds nearer to the shoulder-blade, whilst in 

 others it runs nearly over the middle of the humerus. The latter is the case in the Passerine 

 birds amongst others (Plate III) ; the former in the GallinaR (Plate VII), and Columba. Scarcely 

 any great differences occur, however, in the humeral tracts. They are usually the strongest of 

 all the tracts, except those which bear the remiges and rectrices, and this is seen particularly at 

 their posterior extremity, where the axillary feathers, which lie upon the wing in its folded position, 

 and which are characterised by their thick tubes, are inserted into it. The few differences of 

 form which I have been able to discover in the humeral tracts, are founded upon the number, 

 size, and degree of approximation of these feathers. I find it strong and broad in the Rapacious 

 birds, especially the Falcons (Plate II), in the Waders (Plate VIII), such as Ardea leuce, 

 A. egretta, and A. garzetta, which possess peculiar, very large axillary feathers, and in the 

 Longipennes (Plate IX) ; it is much weaker in the Passerine and CuculineB (Plates III V) ; and 

 generally very small, but also sometimes very large (as in Cofymbus), in various Pygopodes (Plate X). 

 The genus Picus (Plate V, fig. 15) is remarkable for its double humeral tract on each side, namely, 

 a small inner one and a much larger outer one, both of which pass into the plumage of the great 

 wing-membrane. In some birds, as, for instance, the Steganopodes (Plate X), and in Buceros 

 and Colius, which possess a very broad spinal tract, the humeral tracts are united to the latter, 

 but may nevertheless be recognised as distinct tracts by the stronger formation of their feathers. 



III. THE FEMORAL OR LUMBAR TRACT (Pteryla femomlis sew lumbalis). 



Like the preceding always double, right and left, this tract forms a long, oblique band on 

 the outer side of the thigh ; its extension varies in both directions, and it is bounded by parts of 

 the lateral space of the trunk. It varies in many ways. 



1. Narrow, simple, straight, and oblique, that is to say, not parallel to the median 

 line of the back, but rather tending to meet it if prolonged in imagination. In this form it 

 may be : 



4 



