30 PTERYLOGRAPHY. 



space; the branch long, rounded at the end, separated by a narrow cleft from the pectoral band, 

 to which it runs parallel. I have seen this kind of ventral tract in Uria. 



15. With a branch ; distinct, and divided into a right and left band, even on the neck ; each 

 of these bands, on reaching the breast, emits a very large, broad, acute, lanceolate branch ; the 

 pectoral band, on the contrary, is very narrow or mucli weakened, and separated by a true or false 

 gap from the branch. This form occurs especially in the gallinaceous birds (Plate VII), but not 

 in all of them. 



16. With a branch, and narrow; the branch very distinctly separated, but curved and 

 united again with the stem posteriorly, so as to enclose an insular space. I have found this 

 remarkable form of the ventral tract in the Disk-Owls (Ht/lris, Plate II, fig. 11), in Crotopliaga, 

 Coccygius (Guird), and Saurothera (Cuculus viaticus, LICHT). It is similar also in Scythrops (Plate 

 IV, fig. 15) ; but the insular space is here clothed with isolated feathers, and thus weakened. 



17. Irregular, inasmuch as the gular portion is wanting, its place being taken partly by the 

 lateral neck-tracts, and partly by the cervical portion of the spinal tract. Thus the ventral tract 

 consists entirely of a narrow pectoral band, with or without a branch, separated from its neighbour 

 by a broad ventral space, and united anteriorly with the humeral and spinal tracts. I have 

 found this very peculiar structure only in the Herons (Erodii). The pectoral bands are sometimes 

 separated by a false gap from the lateral neck-tracts, as in Ardea stellaris, minuta and scapu- 

 laris, and Cancroma cochlearia ; and sometimes united with them, as in Ardea cinerea, A. 

 purpurea, and other thin-necked Herons. A complete branch occurs only in Cancroma ; in 

 Ardea it is either entirely wanting or very imperfect (Plate VIII, figs. 10, 12, and 13). 



V. THE LATEKAL NECK-TRACT (Pteryla colli lateralis). 



This occurs only in a few birds, namely, the above-mentioned Herons and the Little Bustard 

 ( Otis tetrax) ; it is always paired, left and right. Properly speaking, it does not constitute a 

 distinct tract, but is produced by the union of the spinal and ventral tracts, when both of these 

 are divided throughout their whole length by broad spaces, and the lateral neck-spaces are 

 wanting. In the tldn-necked Herons, therefore, these lateral neck-tracts pass without any 

 interruption into both the spinal and ventral tracts of each side; in the thick-necked forms 

 (Butaurus), on the contrary, at least in Ardete stellaris, minuta, and scapularis, they are 

 separated from both by a false gap (Plate VIII). In Ardea iiycticorax and Cancroma the 

 arrangement occupies a middle place between the two forms ; for in these the lateral neck-tracts 

 are only continued into the spinal tract, and not into the pectoral bands of the ventral tract. In 

 Cancroma they are also united in a peculiar manner at the end of the neck, so that they enclose 

 a median neck-space. 



The tracts which we have hitherto had under consideration are those which especially 

 deserve the name, and I believe that their description would suffice for the representation of the 

 different kinds of interrupted plumage ; the other tracts, namely, those of the head, wings, and 

 tail, usually consist of a scarcely interrupted or perfectly continuous plumage, and require no 

 further detailed description. Nevertheless, any one with a predilection for uniformity of nomen- 



