10 TRICHOLOGIA MAMMALIUM ; 
2d. A stalk, situated anteriorly to the cylinder, the shape of which inclines more or less 
to square, being slightly curved on one side. It gradually diminishes in circumference, 
from the superior navel to the anterior extremity. The face imszde of the curve is called 
the enternal face, 2nd that on the opposite side, the external face. ‘These two faces are 
united by a horny matter, somewhat resembling that of the cylinder; but generally less 
transparent. In the interior of it is a white opaque, soft, elastic substance, called the 
“mith,” or “sponge” of the feather. The surface of the external face is smooth, and forms 
the segment of a circle, being sometimes longitudinally striated. ‘The internal face is, 
generally, for its whole length, divided into two equal parts or sections, by a longitudinal 
canal. Occasionally, instead of the canal, there is a projection of the same dimensions. 
3d. On each side of the stalk is a beard and a steno-beard. The fibrils of the steno- 
beard are generally crooked, giving them a tendency to entangle and adhere. 
Ath. A feather possesses flexibility and tenacity, but no ductility nor elasticity. 
By comparing this description of a feather with the previous one of a hair, we will 
readily perceive the differences between these two integuments. 
Or tHe DirFERENCE BETWEEN A Hair and A FEatHER.—(Compare figs. 1 and 3.)—A 
feather and a hair differ in these particulars :— 
Ist. A feather, at the inferior extremity of the cylinder, has a perforation, but no button ; 
a hair, at the same extremity of the shaft, has a dutton, but no perforation. 
2d. A hair is set in a follicle ; but a feather has none. 
3d. A feather has, at the point where the cylinder unites with the stalk, a seperzor navel ; 
a hair has no such perforation. 
4th. The stalk of a feather has two different faces, an external and an internal one; a 
hair is the same for its whole contour. 
5th. A feather has, in its cylinder, a serves or chain of capsules, which, in a hair, is 
entirely wanting,—except in one solitary instance, which will be presently noticed. 
6th. The stalk of a feather is provided with a pith or sponge ; which in a hair is entirely 
wanting. 
7th. The stalk of a feather has, on its interior face, a canal; which, in a hair, is entirely 
wanting. 
Sth. A perfect hair has, in its centre, a canal, in which the coloring matter, when pre- 
sent, flows; a feather has none. 
9th. The exterior of the shaft of a feather is smooth, and the steno-beard is generally 
hooked; the cortex of the shaft of a hair is squamose. 
10th. The stalk of a feather is furnished with a deard and a steno-beard; a hair has 
neither. 
11th. The stalk of a feather gradually diminishes in diameter anteriorally ; but a hair is, 
generally, of the same diameter throughout. (There are exceptions. ) 
12th. A feather has flexibility and tenacity, but no ductelty nor elasticity ; a hair has 
ductility, flexibility, elasticity and tenacity. 
