xm PHYLUM CHORDATA 487 



movements being restricted, by the nature of the articulations, to 

 antero-posterior movements of flexion and extension. The meta- 

 carpal and metatarsal regions are relatively very long. In the 

 Artiodactyla the third and fourth digits of each foot form a sym- 

 metrical pair. In the Ruminants vestiges of the second and fifth 

 digits are also commonly present ; but these are usually not func- 

 tional, never reaching the ground, though in the Reindeer they are 

 better developed than in the others and have the effect of preventing 

 the foot from so readily sinking in the snow. In the Camels the 

 third and fourth digits alone are present. The Giraffes are dis- 

 tinguished from the other Ruminants by the enormous length of the 

 neck. Characteristic of the Ruminants, though absent in the Camels 

 and some others, are the cephalic appendages known as horns and 

 antlers. The horns of the Hollow-horned Ruminants (Oxen, Sheep, 

 Goats, Antelopes), sometimes developed in both sexes, sometimes 

 only in the males, are horny sheaths supported by bony cores which 

 are outgrowths of the frontal bones. In the Giraffe the horns, which 

 are short and occur in both sexes, are bony structures covered with 

 soft skin, and not at first attached by bony union to the skull, 

 though subsequently becoming firmly fixed. Between them is a 

 short rounded median bony protuberance on the frontal region of the 

 skull. The antlers of the Deer, which, except in the case of the 

 Reindeer, are restricted to the male sex, are bony growths covered 

 only while immature by a layer of skin, the " velvet," provided with 

 very soft, short fur. Antlers are shed annually, and renewed by 

 the growth of fresh vascular bony tissue from the summit of a 

 pair of short processes of the frontal bones, the pedicles. Even- 

 tually, when the antlers are full grown, a ring-like thickening of the 

 bone, the " burr," appears round the base of the antler, and con- 

 stricts the blood-vessels, so that the substance of the antler becomes 

 converted into dry, dead bone ; the skin shrivels and is peeled off. 

 The antler is shed by the absorption of the bone immediately 

 beneath the burr. The pinnae of the ear of the Ruminants are well 

 developed. The tail is sometimes elongated and provided with a 

 terminal leash of long coarse hairs ; sometimes short and bushy. 

 The entire surface, with the exception of the end of the muzzle, 

 which is naked, is always covered with a close coat of longer or shorter 

 hairs. 



In the Pigs the legs are relatively short, and the two lateral 

 toes of both manus and pes are fully developed, though scarcely 

 reaching the ground. The surface is covered with a scanty coat 

 of coarse bristles. There is a truncate, mobile snout, the anterior 

 end of which is disc-shaped and free from hairs. The pinnae are 

 large ; the tail is rather long, narrow, and cylindrical, provided 

 with a terminal tuft of strong hairs. A remarkable feature of the 

 males is the development of the canine teeth of both jaws into 

 large, upwardly-curved tusks. In the Peccaries, which resemble 



