We have not in many cases so rich a collection of intermediate forms as in the case of the horse, but our fossil mammals are numerous enough to suggest a similar development of all the mammals of to-day. The primitive family which gave birth to the horse also gave us, as we saw, the tapir and the rhinoceros. We find ancestral tapirs in Europe and America during the Tertiary period, but the later cold has driven them to the warm swamps of Brazil and Malaysia. The rhinoceros has had a long and interesting history. From the primitive Hyrochinus of the Eocene, in which it is dimly foreshadowed, we pass to a large and varied family in the later periods. In the Oligocene it spreads into three great branches, adapted, respectively, to life on the elevated lands, the lowlands, and the water. The upland type (Hyracodon) was a light-limbed running animal, well illustrating the close relation to the horse. The aquatic representative (Metamynodon) was a stumpy and bulky animal. The intermediate lowland type was probably the ancestor of the modern animal. All three forms were yet hornless. In the Miocene the lowland type (Leptaceratherium, Aceratherium, etc.) develops vigorously, while the other branches die. The European types now have two horns, and in one of the American species (Diceratherium) we see a commencement of the horny growths from the skull. We shall see later that the rhinoceros continued in Europe even during the severe conditions of the glacial period, in a branch that developed a woolly coat. There were also in the early Tertiary several sidebranches of the horse-tapir-rhinoceros family. The Palaeotheres were more or less between the horse and the tapir in structure; the Anoplotheres between the tapir and the ruminant. A third doomed branch, the Titanotheres, flourished vigorously for a time, and begot some strange and monstrous forms (Brontops, Titanops, etc.). In the larger specimens the body was about fourteen feet long, and stood ten feet from the ground. The long, low skull had a pair of horns over the snout. They perished like the equally powerful but equally sluggish and stupid Deinocerata. The Tertiary was an age of brain rather than of brawn. As compared with their early Tertiary representatives' some of our modern mammals have increased seven or eight-fold in brain-capacity.