MAMMALIA. 295 
ribs, that in turn-inclose and protect the chest. Third, 
the lumbar or loin vertebre, numbering from four to 
seven. Fourth, the sacral bones, that are anchylosed and 
form the sacrum; these generally number from one to 
nine, Fifth, the caudal or tail vertebra, that are more 
movable one upon another than the others, and number 
from four to forty-six. The tail is a very useful member. 
In some of the monkeys it serves as a fifth hand; in the 
dog it is used to express emotion, and in the horse, ant- 
eater, and many animals, as a protection from insects. 
Limbs.—The mammals generally have four limbs, and 
from this are termed quadrupeds, though in the whale the 
hinder pair are not present, or are rudimentary. In Fig. 
321 we see the fore-limb joined to the body by the shoul- 
der-blade or scapula, sc, and the clavicle or collar-bone. 
The first bone of the leg is the humerus, 1; then follow 
two bones joined together, the radius and ulna, 2, followed 
in turn by the carpus, 3, or wrist-bone, the metacarpals, 
that. form the upper portion of the hand, and the phalan- 
ges, 4, or finger and toe bones. The hind-limbs in their 
parts resemble the fore ones, and are connected to the 
body by a number of bones that are joined together and 
known as the innominate bone, z, and constitute the pelvic 
arch. The upper bone of the leg is the femur or thigh, 
5; then follow the leg-bones, similar to the ulna and 
radius, but called the tibia and fibula, 6 ; then the tarsus 
or ankle-bones, 7, the metatarsus or bones of the foot, 8, 
and the bones of the toes or phalanges, 9. There are gen- 
erally five toes, but there are many exceptions, as the 
horse that walks on the toe-nail of its single toe, the ox 
on two toes, etc. The limbs are adapted to the habits 
of the animal. The sloths have long claws for clinging, 
and the moles powerful digging-claws. In the whales and 
seals they are paddles. 
Digestion.—The jaws of all mammals, except the whale- 
bone whales and a few others, are provided with teeth 
