. Zoology for high schools and colleges. Zoology. 562 ZOOLOGY. they are sometimes called Cavicorns. In most horned mammals, the horns are persistent; in the deer they are dropped annually ; in the prong-horned antelope (Fig. 487) the horns are also shed annually. The mammary glands are modiiications of the tegument- ary glands which are found in all vertebrates except fishes. In the duckbill and spiny ant-eater (Echidna), these glands retain their simple elementary nature. In all others nip- ples are developed (Fig. 486). They correspond in general to the number of young in a litter. The denti
. Zoology for high schools and colleges. Zoology. 562 ZOOLOGY. they are sometimes called Cavicorns. In most horned mammals, the horns are persistent; in the deer they are dropped annually ; in the prong-horned antelope (Fig. 487) the horns are also shed annually. The mammary glands are modiiications of the tegument- ary glands which are found in all vertebrates except fishes. In the duckbill and spiny ant-eater (Echidna), these glands retain their simple elementary nature. In all others nip- ples are developed (Fig. 486). They correspond in general to the number of young in a litter. The dentition needs careful study in connection with the Fig. 488.—Skull of Ant-eater.—After Owen. Fig. 487. - HoUow horn of the Prong horned Fig. 489.—Skull of a Owen. fossil remains of mammals, as the different orders are char- acterized in great part by the differences in the form and number of the teeth, which are intimately correlated with the structure of the digestive organs and the nature of the limbs ; thus while vertebrse are useful in identifying or re- storing fossil reptiles, the teeth are especially serviceable in classifying fossil mammals. Some existing forms are en- tirely toothless, as the duckbill, where the teeth are repre- sented by horny plates, and the ant-eater (Fig. 488). While the sloths have no incisors, these are present and very large in the rodents, but the canines are absent (Fig. 489).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Packard, A. S. (Alpheus Spring), 1839-1905. New York, H. Holt and Company
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