A dermal bone- bony structures derived from intramembranous ossification

Intramembranous ossification

Intramembranous ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike endochondral ossification, which is the other process by which bone tissue is created, cartilage is not present during intramembranous...

 that form components of the vertebrate

Vertebrate

Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

 skeleton including the skull, jaws, gills, fins and exoskeleton. In contrast to endochondral

Endochondral ossification

Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral...

 bone, dermal bone does not form from cartilage first and then calcify. Dermal bone is formed within the dermis

Dermis

The dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...

 and it grows by accretion only; that is, the outer portion of the bone is deposited by osteocyte

Osteocyte

An osteocyte, a star-shaped cell, is the most abundant cell found in compact bone. Cells contain a nucleus and a thin ring of cytoplasm. When osteoblasts become trapped in the matrix they secrete, they become osteocytes...

s.

The function of dermal bone is conserved throughout vertebrates, varying in shape and numbers of bones in the skull roof

Skull roof

The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...

 and postcranial structures. In bony fish, dermal bone is found throughout the body in the fin rays and scales. Special examples of dermal bones include the clavicle

Clavicle

In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...

, patella, and os cordis.