THE PYGOPODES. 153 



strong limbs reach to the end of the shoulder-blades ; the very broad posterior part is much 

 shorter, and does not attain the shoulder-blades. 3. The broader tail bears definitely distin- 

 guishable rectrices, the number of which is eighteen or twenty. 4. On the pinion of the 

 wing there are probably only ten feathers, and the total number of remiges is more than 

 thirty. 



b. The inferior tract-lands have a distinct, and even long, but narrow outer branch. 



In the members of this group, to which the genera Uria, Alca, Phaleris, and Mormon belong, 

 the ptilosis continua extends to the middle of the neck. Here it is interrupted by the lateral 

 neck-spaces which reach to this point, and soon afterwards the inferior space also commences, whilst 

 the spinal space does not advance beyond the limits of the trunk. The inferior tract, the division 

 of which thus becomes visible a little in front of the jugular region, consists of two broad, densely 

 feathered bands (PL X, fig. 13), the feathers of which present the ordinary arrangement of 

 oblique rows, which run parallel to each other and to the crest of the sternum as far as 

 the anus, in front of which they terminate, separated only by the very narrow inferior space. 

 Exteriorly each band is from the first as broad as the entire pectoral surface, and is, therefore, con- 

 nected by its anterior extremity with the axillary tracts. From this point the band is continued 

 beneath the axillary cavity, embraces the shoulder-joint in front, and extends over the sides of 

 the trunk as far as the knee-covert, gradually becoming somewhat broader behind. This greater 

 breadth is, however, only apparent, for a continuation of the lateral space of the trunk pushes 

 itself from the knee-covert into the tract in such a manner that the latter is divided into two 

 approximated parallel bands. The inner -of these bands, which passes without interruption from 

 the surface of the breast upon the belly, and here usually increases somewhat in width, is 

 unquestionably the main stem ; the outer one, on the contrary, must be described as the pectoral 

 branch, which is elsewhere usually much shorter and comparatively wider. In Alca torda, which 

 has been selected for the pictorial representation of these conditions, the main stem is rather 

 narrow in comparison with the branch, but still evidently broader than the latter. This proportion 

 is greatly increased in Alca impennis, but is less marked in Uria and Mormon, in which both 

 bands have nearly the same width. In every respect Alca impennis differs more from its relations 

 in the group, especially in the remarkable dilatation of the main stem upon the ventral surface, 

 which penetrates backwards in an acute angle into the inguinal region, and gives the ventral 

 portion of the two bands the appearance of a broad arrow-head. This species has also the 

 narrowest inferior space ; indeed, all its spaces are very narrow. 



The spinal space in this group does not differ essentially from that of the Unguirostres and 

 Steffanopodes ; it is uninterrupted, of equal strength throughout, and widened behind, where it is 

 coalescent with the lumbar tracts, and through these with the plumage of the tibia. In Mormon 

 arcticus the spinal space appeared to be wanting ; but in the other genera it made its appearance 

 in the dorsal tract, between the shoulder-blades, in the form of a narrow band, which usually 

 reached to the caudal pit (PL X, fig. 14), but in Alca impennis only to the commencement of the 

 pelvis. This species, which is so remarkable for the small size of its wings, has, nevertheless, 

 from twenty-nine to thirty remiges, ten of which are primaries. I found the same number of 

 remiges in A. torda and Uria grylle ; but U. troile and U. alle have only twenty-six, of which 

 eleven appeared to be primaries, as also in the other species. The number of tail-feathers in the 



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