. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 234 Biology of the Vertebrates. Fig. 174. Head of a male lizard, Cera- tophora stoddaerti, with a horn on its snout. (After Dar- win.) indicates, sported a horn over each eye and a third one on its nose (Fig. 36f and h). Even among modern reptiles there are a few rare bizarre lizards with nose horns, for example Chamaeleon oweni and Ceratophora stoddaerti (Fig. 174). The "horned toad," Phrynosoma, of our southwestern desert region, also a lizard
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 234 Biology of the Vertebrates. Fig. 174. Head of a male lizard, Cera- tophora stoddaerti, with a horn on its snout. (After Dar- win.) indicates, sported a horn over each eye and a third one on its nose (Fig. 36f and h). Even among modern reptiles there are a few rare bizarre lizards with nose horns, for example Chamaeleon oweni and Ceratophora stoddaerti (Fig. 174). The "horned toad," Phrynosoma, of our southwestern desert region, also a lizard and not an amphibian as its name would imply, is another reptilian specialist in horns (Fig. 43). Aside from these few cases of horned lizards, horns are peculiar to mammals and are coupled with hoofs that characterize the ungulates. In early Triassic times certain ungulates that lived in North America outdistanced dinosaurs in the num- ber of their horns. Dinoceras, for example, had six large horns on its head. It is probable that these conspicuous bony projections were capped over by horny sheaths, although positive evidence is not furnished by the fossils of these animals. There are four general kinds of ungulate horns known today, namely, keratin-fiber horns, antlers, pronghorns, and hollow horns. (a) Keratin-Fiber Horns. Keratin-fiber horns are made up of hairlike keratin fibers produced from the corneal layer of the epidermis and cemented together in a hard compact mass. They are entirely epidermal and have no bony core. The Indian rhinoceros carries one of these horns on its "nose," as its name indicates (rhino, nose; ceros, horn), while the African rhinoc- eros has two, arranged tandem-fashion instead of side by side in the con- ventional way of paired structures (Fig. 66c and d) . It is reported that Bos triceros, one of the kinds of native African cattle, also has a median horn of this curious type, as its species name indicates. (b) Antlers. Antlers are com
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