i8 Field Museum of Natural History — Zoology, Vol. 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 shall, 

 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 

 epidennis,"^ 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 squainate. In some 

 species of Bats (Molossidce) 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 Vespertilionidce, 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 piginent produces a white (albinistic) one, which should 

 normally be of some other color. Coinparatively few mainmals are 

 *For definition see Glossary, p. 489. 



