The following characters are also very nearly universal, and in any case absolutely distinctive:--Cervical vertebrae, seven; vertebrae with epiphyses. Ankle-joint "cruro-tarsal," _i.e._ between the leg and the ankle, and not in the middle of the ankle.[1] Attachment of the pelvis to the vertebral column pre-acetabular in position. The Mammalia since they are hot-blooded creatures are more independent of temperature than reptiles; they are thus found spread over a wider area of the earth's surface. As however, though hot-blooded, they have not the powers of locomotion possessed by birds, they are not quite so widely distributed as are those animals. The Mammalia range up into the extreme north, but, excepting only forms mainly aquatic, such as the Sea Lions, are not known to occur on the Antarctic continent. With the exception of the flying Bats, indigenous mammals are totally absent from New Zealand; and it seems to be doubtful whether those supposed oceanic islands which have a mammalian fauna are really {4} oceanic in origin. The continents and oceans are peopled by rather over three thousand species of Mammalia, a number which is considerably less than that of either birds or reptiles. It seems clear that, so far at any rate as concerns the numbers of families and genera, the mammalian fauna of to-day is less varied than it was during the Mid-tertiary period, the heyday of mammalian life. It is rather remarkable to contrast in this way the mammals and the birds. The two classes of the animal kingdom seem to have come into being at about the same period; but the birds either have reached their culminating point to-day, or have not yet reached it. The Mammalia, on the other hand, multiplied to an extraordinary extent during the Eocene and the Miocene periods, and have since dwindled. The break is most marked at the close of the Pleistocene, and may be in part due to the direct influence of man. At present man exercises so enormous an effect, both directly and indirectly, that the future history of the Mammalia is probably foreshadowed by the instances of the White Rhinoceros and the Quagga. On the other hand, the economic usefulness of the Mammalia is greater than that of any other animals; and the next most important era in their history will be probably that of domesticity and "preservation." * * * * * {5} CHAPTER II STRUCTURE AND PRESENT DISTRIBUTION OF THE MAMMALIA