An adult black rhinoceros normally has two horns.
The black rhinoceros (Diceros bicornis) has a larger front horn and a smaller rear horn, both growing from the skin rather than being attached to the skull like true bony structures. The front horn can be substantially longer than the second, although horn size varies among individuals and populations.
Rhino horns are made primarily of keratin, the same structural protein found in human hair and fingernails. They do not contain a solid core of bone. Rhinos use their horns for defense, competition, and possibly moving branches or soil.
The black rhinoceros is smaller and more hooked-lipped than the white rhinoceros, but both African species normally have two horns. The names black and white do not reliably describe their color; they are commonly explained as historical confusion involving the shape of the animals’ lips and words used by early observers.