How do bovid horns grow from the skull?

Bovid horns are permanent, unbranched structures that grow from the frontal bones of the skull. Unlike the antlers of deer, which are solid bone and shed annually, bovid horns consist of a bony core that serves as a permanent extension of the cranium.1234

This bony core is covered by a protective, hollow sheath made of keratin—the same protein found in fingernails and hair. This sheath is produced by the epidermis and fits over the bony core. Because these horns are a permanent part of the animal's anatomy, they are not shed; if a horn is accidentally lost, it does not regenerate. In most bovid species, these horns continue to grow throughout the animal's life.14325