RE: What Do You Call Them ?
... About Antlers
Antlers grow from the pedicle, a bony platform above the frontal bone of the skull. They begin growing in late April or May, and start branching about two weeks later. By the end of May, they are well developed and covered with "velvet," a covering of skin with nerves and blood vessels. By August, the growth period ends and the velvet begins to dry at the tips.
When the antlers are fully hardened, the velvet dies and starts to peel off in shreds. Once it is completely lost, the mating season begins. When mating season is over, the pedicle begins to separate from the skull and breaks off as a complete set when the animal bumps into something.
Only a few embryonic cells are left and these form the basis of a new pedicle and antlers, which begin growing about six weeks later. If you visit Sagamore Hill, there is a place outside the library where you can see a set of antlers still attached to the pedicle.
...About Horns
Horns, on the other hand, are made up of tubular filaments of keratin, the same substance that makes up human hair and nails. Horns are usually hollow; only the rhinoceros has solid horns (if you look at the base of the White Rhino horn, such as the one a Sagamore Hill hall, you can see where the filaments join).
Horns grow throughout an animal's life; however, if the tip or point of a horn breaks for any reason, it will not re-form. Horns have only one point. The exception to this rule is the Pronghorn Antelope of the American plains. Not only do their horns have two points (hence the name Pronghorn), but they also shed their horns on a regular basis.
So what about the giraffe? Horns or antlers? The two hairy lumps between the ears of the giraffe are neither antlers nor horns, but two hairy, fleshy lumps between the ears!