The majority of mammals have a number of large, long hairs, or vibrissm, arranged in a definite fashion about the mouth, eyes and ears, which serve to a certain degree as tactile organs. In deer and some other ruminants the hairs consist mainly of the cellular pith aa hence are easily broken.
The color of mammals is chiefly due to the pigments contained in the hair, which belong to the class known as melanins. Black, white and brown in various mixtures and shades are the commonest colors. The coloration is chiefly protective, but some such sharp contrasts of black and white as those of the skunks are thought to be warning colors, and the dear white of the under side of the tail of deer. certain hares, etc., to be directive, or guishing, marks for the young.
The skeleton consists of an axial portion, comprising the skull, the back bone or vertebral column, the ribs and the sternum; and an appendicular portion or the skeleton of the limbs. In the skull the bones are bound firmly together by the overlapping or interdigitation of the edges, except the lower jaw, the ossicles of the internal ear and the hyoid, or tongue, bones. In adults most of the sutures are usually obliterated. The snout or rostrum consists of the premaxillary, maxillary, palatine and pterygoid bones below and on the sides, and the nasals above, while within are the median vomer and the ethmoid bones. The rostrum abuts against the brain-case or cranium, which is vaulted, and comprises three segments, an anterior one, consisting of the presphenoid, orbito-sphenoids and frontal;, a middle segment, consisting of the alisphenoids, squamosals and parietals; and, a posterior segment, consisting of the ital, exoccipitals and supra-occipital. The ex occipitals bear the two condyles for articulation with the vertebral column. At the base of the skull, between the occipital and squamosal, are the periotic bones, containing the organ of bearing or internal ear, and the tympanics, which form the bony walls of the orifice of the ear. The tympanics are greatly expanded in whales and some other mammals, forming shell-shaped bull.a.
The vertebral column comprises five sections, the cervical, dorsal (or thoracic), lumbar, sacral and caudal. The cervical vertebra are seven in number in all mammals, whatever the length of the neck, the only exceptions being the man atees, which have six, and the sloths, which have six, eight or nine. In certain whales, the majority of porpoises and some rodents, the cervicals are more or less united; in the right whales they form a single bony mass. The dorsals vary in number from 9 to 22. Articu lated with each is a pair of ribs. The ribs terminate below in cartilages, which sometimes ossify, forming what are called By means of these cartilages the anterior pairs of ribs are connected with the breastbone or sternum, which may consist of a single piece, as in the whalebone whales, or of several seg ments arranged longitudinally. The posterior pairs of ribs are sometimes called 'floating ribs* because their cartilages do not meet the ster num, but are attached to those of the more anterior pairs, or are quite free. The lumbar vertebra follow the dorsals and are without ribs. In number they vary from 2 to 30 in different forms. The number of dorsal and lum
bar vertebra combined is quite constantly 23 in the odd-toed ungulates (horse, rhinoceros, tapir, etc.), 19 in even-toed ungulates (deer, ox, sheep, etc.), and 20 or 21 in carnivores and most insec tivores. Man, the higher apes and many bats have 17. Following the lumbars is the sacrum, consisting usually of three vertebra joined to gether and connected with the pelvis. This region is not distinguishable in the whales and sea-cows, which lack hind limbs. The caudals, or tail-vertebra, complete the column. In man and in certain apes and bats they are three in number and rudimentary, but as many as 46 are present in the long-tailed pangolins. In the intervals between the anterior caudals be low are situated small V-shaped bones, called chevrons, whose chief function is to protect the larger blood-vessels of the tail. They are espe-, cially well developed in the whales and eden tates.
In many groups of mammals the anterior limbs are connected with the axial portion of the skeleton through the pectoral girdle, consist ing of the shoulder blades, or scapula, and the collar-bones or clavicles. The scapula is not at tached directly to the vertebral column, but its acromion process is joined to the anterior of the breastbone, or sternum, by means of the clavicle. Clavicles are wanting in all seals, whales, sea-cows and ungulates, and are rudi mentary or wanting in various representatives of several other groups. They are present in man and, with one or two exceptions, in all monkeys, bats, insectivores and marsupials. The upper-arm bone, or humerus, articulates superiorly with the scapula, and below with the two bones of the fore-arm, the radius and ulna. In the majority of mammals the radius, or outer bone, is permanently crossed over the ulna at the lower end, as is especially well Seen in the elephants. In man and a few other forms the radius can be rotated. Fol lowing the fore-arm is the wrist or carpus, consisting of three rows of small bones, which, however, are variously united in different forms; and finally the digits, which are nor mally five in number, each consisting when fully developed of a metacarpal bone and three other bones, or occasionally more, called pha langes, though the first digit, or thumb, usually has but three in all. In man and apes the thumb is opposable to the other digits. In many mammals this digit and also the fifth are greatly reduced, or entirely wanting. In the ruminants, such as the pig, ox, deer, camel, etc., the first digit is wanting, and the second and fifth are reduced in size, or entirely lack ing, while the third and fourth are equal in length and well developed. In the odd-toed ungulates, such as the horse, rhinoceros, tapir, etc., the third digit is longest, the others being reduced in length, rudimentary or wanting. In ungulates the metacarpals are usually much elongated and in such ruminants as the deer, ox, etc., are united, forming what is known as a The cetacea are peculiar in that the bones of the fore-limb are not mov ably articulated and that the phalanges of the middle digits often greatly exceed three. In bats the phalanges are very greatly elongated to give support to the wing membranes.