xiii PHYLUM CHORDATA 473 



alone are present. The Giraffes are distinguished 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 on bony cores, which are outgrowths 

 of the frontal bones. In the Giraffes 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 enclosed 

 only while immature in a layer of skin, the " velvet," covered 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 fully grown, a ring-like thickening of 

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

 constricts 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 pinna? 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 pinna? 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 

 the Pigs in most of the features mentioned, the points of the upper 

 tusks are directed downwards. 



In the Hippopotami the body is of great bulk, the limbs 

 very short and thick, the head enormous, with a transversely 

 expanded snout, prominent eyes, and small pinnae. The tail 

 is short and laterally compressed. The toes are four in each 

 manus and pes, all reaching the ground. The surface is naked, 

 with only a few hairs in certain positions ; the skin is of great 

 thickness. 



