108 PTERYLOGRAPHY. 



b. Dorsal tract much contracted, especially its Under part, wJiich forms a very narrow, biserial 



band. 



Here I place the genus Opistliocomus, which is anomalous in many respects. The 

 figure of its pterylosis (Plate VI, figs. 12 and 13) shows that the continuous plumage of the 

 head, which is very sparse, but denser on the vertex, is continued upon the neck, and does not 

 allow the formation of lateral neck-spaces. From the lower extremity of this neck-plumage the 

 inferior tract commences as two broad bands, which run down close to the keel of the sternum, 

 and become somewhat stronger at the outer margin where the branch would be situated. At 

 the end of the sternum these are narrowed, and pass on, gradually becoming weaker, to the 

 anus, at which they terminate with a breadth of only two feathers. Both on the tract itself and 

 on the spaces between its bands, true down-feathers are placed, although not very closely. The same 

 sparse condition is exhibited also by the lumbar tracts and the plumage of the crura and wings ; 

 but the narrow axillary tracts and the dorsal tract contain more closely approximated, although 

 smaller feathers. The latter starts as a strong, triserial band from the midst of the plumage of 

 the lower part of the neck, and divides between the shoulders into two limbs, with which the 

 originally divergent feather-rows of the biserial hinder part are united at the endj from the 

 caudal pit onwards it becomes somewhat broader, and encloses the oil-gland, which is larger, and 

 has a circlet of feathers at the tip, stronger than in the preceding genera. In the wings there 

 are nineteen remiges, of which ten are on the pinion ; the first four are graduated, and the fifth 

 and sixth the longest. The tail has ten large rectrices. 



CHAPTER IV. 

 PIGEONS Columbina. 



BUT few, and these not very important, peculiarities can be indicated as the pterylo- 

 graphic characters of the Pigeons, with which I unite the Sand-grouse (Pterocles and Syrrhaptes) -. 

 indeed, it appears to me that except the very broad form of the tracts which closely cover more 

 than half the surface of the body, the small, non-mamelliferous and perfectly naked oil-gland 

 alone furnishes a good group-character. Both the Pigeons and Sand-grouse, indeed, are entirely 

 destitute of down ; but the after-shaft, which occurs in the latter, is wanting in the former. 

 On the other hand, the two forms agree in the furcate form of the anterior part of the spinal 

 tract, and the remarkable weakening of its hinder part, which commences between the branches 

 of the fork; but a very similar structure is possessed by certain Gallinaceas, such as Numida and 

 Penelope. The number of remiges varies from twenty-one to twenty-eight, and that of the 

 rectrices from twelve to sixteen. 



