18  Frerp Museum or Natura History — Zoétocy, Vot. XI. 
external and internal structure before proceeding to take up the study 
of the living mammals. It is obvious that adequate treatment of such 
a great subject as mammalian anatomy would be impossible in any such 
condensed form as would be necessary, if attempted here. I shail, 
therefore, confine myself to brief remarks (which are intended for the 
use of beginners only) concerning those parts which will be referred to 
later in connection with the descriptions of the families and genera 
included in this work. 
TEGUMENTARY STRUCTURES. 
Hoofs, Claws and Nails — These are hard, horny modifications of the 
epidermis,* and with few exceptions (Cete) are present on the 
terminal extremities of the digits. They vary greatly in character, 
but it is unnecessary to discuss them here, as the differences in the 
various species which occur within our limits are described later. 
Hair — A hair may be considered as an outgrowth of the epidermis, 
elongated and generally cylindrical in shape, and extends from a 
papilla at the bottom of a follicle in the true skin,* but in some cases 
it is flattened and not round, as illustrated in the curly haired races 
of Men, a few of the Rodents and some others. With few exceptions 
the outer surface is hard and the inner portion cellular, surrounded by 
a cortex, the latter containing the color pigment, and is covered 
by a cuticle which may be smooth or rough and squamate. In some 
species of Bats (Molosside) for example, the hair when viewed under 
a powerful microscope shows rings or zones of verticulate spinules; 
while in our species, belonging to the family Vespertilionide, the 
spinules are arranged in a continuous spiral, or in imbricated trian- 
gles and often in various other patterns (see illustration, p. 446). 
Hairs vary enormously in size and degree of rigidity in different 
mammals; as take for examples the soft fur of the Mole, the bristles 
of the Pig, and the spines or quills of the Porcupine, all of which 
are merely modified forms of the same structural growth; and it is 
probable that a still further modification has developed the horns 
of the Rhinoceros. In color the various shades of brown predomi- 
nate. Bright colors are the exception and when present are mostly 
confined to orange and red, as illustrated in some South American 
Squirrels and other exotic forms. Usually animals of the same, 
species are uniformly colored, but occasionally an excess of pig- 
mentation results in a black (melanistic) individual, or an absence 
of color pigment produces a white (albinistic) one, which should 
normally be of some other color. Comparatively few mammals are 
*For definition see Glossary, p. 489. 
