EXTERNAL PARTS OF BIRDS.-- TOPOGRAPHY. 
99 
bare in many birds, as the vulturine hawks, and some pigeons ; species of grouse have a bare 
warty supra-orbital space. Among water-birds particularly, more or less of the inteiramal space 
is almost always unfeathered ; the nakedness always proceeds from before backwards. With 
the rare exceptions of a narrow frontal line, and a little space about the angle of the mouth, no 
other special parts of the head than those above given are naked in any North American bird, 
unless associated with general baldness. 
The opposite condition, that of redundant feathering, gives rise to all the various crests 
(Lat., pi. cristcs) that form such striking ornaments of many birds. Crests proper belong to 
the top of the head, but may be also held to include those growths on its side ; these together 
being called crests in distinction to the ruffs, ruffles, beard, etc., of gula or mentum. Crests 
may be divided into two kinds : 1, where the feathers are simply lengthened or otherwise 
(enlarged ; and 2, where the texture, and sometimes even the structure, is altered. Nearly all 
birds possess the power of moving and elevating the feathers on the head, simulating a slight 
crest in moments of excitement. The general form of a crest is a full, soft elongation of the 
coronal featliers collectively; when perfect, such a crest is globular, as in the genus Pyro- 
cephalus ; generally, however, the feathers lengthen on the occiput more than on the vertex 
or front, and this gives us the simplest and commonest form. Such crests, when more par- 
ticularly occipital, are usually connected with lengthening of nuchal feathers, and are likely 
to be of a thin, pointed shape, as well shown in the kingfisher. Coronal or vertical crests 
proper are apt to be rather different in coloratioji than in specially marked elongation of the 
feathers ; they are perfectly illustrated in the king-bird, and other species of the genus Tyran- 
nus. Frontal crests are the most elegant of all ; they generally rise as a pyramid from the 
forehead, as excellently shown in the blue jay, cardinal bird, tufted titmouse, and others. All 
the foregoing crests are generally single, but sometimes double ; as shown in the two lateral 
occipital tufts of the horned" lark, in all the tufted or horned " owls, and in a few cormo- 
rants. Lateral crests are, of course, always double, one on each side of the head ; they are of 
various shapes, but need not be particularized here, especially since they mostly belong to the 
second class of crests, — those consisting of texturally modified feathers. It is a general, though 
not exclusive, character of these last that they are temporary ; while the other kind is only 
changed with the general moult, these are assumed for a short period only, the breeding season ; 
and, furthermore, they are often distinctive of sex. Occurring on the top of the head, they 
furnish the most remarkable ornaments of birds. I need only instance the elegant helmet-like 
plumes of the partridges of the genus Lophortyx ; the graceful flowing train of Oreortyx ; the 
somewhat similar plumes of the night and other herons. The majority of the cormorants, and 
many of the auks, possess lateral plumes of similar description ; these, and those of the herons, 
are probably — in most cases certainly — deciduous ; while those of the partridges above men- 
tioned last as long as the general plumage. These lateral plumes, in many birds, especially 
among grebes, are associated with, and, in fact, coalesce with, the ruffs, which are singular 
lengthening and modifying in different ways of feathers of auriculars, gense and gula ; and are 
almost alvA^ays temporary. Beards, or special lengthening of the mental feathers alone, are 
comparatively rare ; we have no good example among our birds, but a European vulture, 
Gypaetus barhatus, is one. The feathers sometimes become scaly (squamous), forming, for 
instance, the exquisite gorgelets or frontlets of humming-birds. They are often bristly (seta- 
ceous), as about the lores of nearly all hawks, the forehead of the dabchick, meadow-lark, 
etc. A particular set of bristles, which grow in single series along the gape of many birds, 
are called rictal bristles or vibrissce. These occur in greater or less development in most small 
insectivorous birds ; they are large and stiff' and highly characteristic of the family Tyrannidoe, 
or flycatchers; while in some of the goatsuckers (Caprimulgidce) they are prodigiously long, 
and in one species of that family (Antrostomus carolinensis) they have lateral filaments. While 
usually all the unlengthened head-feathers point backward, they are sometimes erect, forming 
