Some of the species described have a very limited range in our country at present, the Deer, for example, being restricted as wild animals to-day to the Scottish mountains and glens and the West Country moors, but even these may be studied as tolerably free animals in the New Forest, Epping Forest, and in many parks such as those at Windsor and Richmond, as well as in private domains. To the Deer we must add the Wild Cat, the Pine Marten, and the Alpine Hare as mammals that must be sought in special restricted areas; but most of the others may be reckoned to be met with, sooner rather than later, in our country rambles. In view of the practice usual in natural histories of arranging the vertebrate animals in a series with the Birds separating the Mammals from the Reptiles, it may at first sight appear incongruous to bring the latter classes together as we have done; but to the present writer the fitness of this arrangement is quite clear. It is widely held that the Mammalia--the highest class of vertebrates, and therefore the most complex of all animals--have been evolved from an extinct group (_Theromorpha_) of Reptiles, whose remains are found in strata of the Permian and Jurassic Periods. There are, it is true, similar evidences furnished by the rocks showing that the Birds had a reptilian origin; but the Birds did not form an evolutionary stage between the Reptile and the Mammal, but evolved side by side with the latter. The existing British Mammals represent the six orders Insectivora (shrews, mole, and hedgehog), Chiroptera (bats), Carnivora (beasts of prey), Rodentia (gnawing animals), Cetacea (whales and dolphins), and Ungulata (hoofed animals). These all agree with the Reptiles and Batrachians in having a many-jointed internal skeleton, a bony framework giving support to a system of powerful muscles; and of this framework the most important feature is the long backbone or vertebral column consisting of a number of bony rings jointed together by outgrowths or "processes," and held in position by strong ligaments. This attachment of the rings by their flat surfaces produces the spine or vertebral column, with a canal on its upper half in which lies the spinal cord. This column, for descriptive purposes, is divided into regions--cervical, dorsal, lumbar, sacral, and caudal. The number of rings or vertebræ in each region varies somewhat in the different classes and orders, but as a rule the cervical or neck vertebræ are seven; the dorsal, to which the ribs are connected, are about thirteen (extreme numbers are nine and twenty-two); the vertebræ of the lumbar or loin region are usually six or seven, but they vary inversely to those of the dorsal from two to twenty-three; the sacral vertebræ (about five) are in the adult fused together into a solid bone (sacrum) of triangular shape; the caudal vertebræ vary from three (man) to nearly fifty, according to the length of tail common to the genus or species.