A dermal bone or investing bone or membrane bone is a bony structure derived from

intramembranous ossification Intramembranous ossification is one of the two essential processes during fetal development of the gnathostome (excluding chondrichthyans such as sharks) skeletal system by which rudimentary bone tissue is created. Intramembranous ossification i ...

forming components of the

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

skeleton A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...

, including much of the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, jaws,

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

covers, shoulder girdle, fin rays ( lepidotrichia), and the shells of turtles and armadillos. In contrast to endochondral bone, dermal bone does not form from cartilage that then calcifies, and it is often ornamented. Dermal bone is formed within the

dermis The dermis or corium is a layer of skin between the epidermis (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from s ...

and grows by accretion only – the outer portion of the bone is deposited by

osteoblast Osteoblasts (from the Greek combining forms for " bone", ὀστέο-, ''osteo-'' and βλαστάνω, ''blastanō'' "germinate") are cells with a single nucleus that synthesize bone. However, in the process of bone formation, osteoblasts fu ...

s. The function of some dermal bone is conserved throughout vertebrates, although there is variation in shape and in the number of bones in the

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, including land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In com ...

and postcranial structures. In

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

, dermal bone is found in the fin rays and scales. A special example of dermal bone is the

clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one on each side of the body. The clavic ...

. Some of the dermal bone functions regard biomechanical aspects such as protection against predators. The dermal bones are also argued to be involved in ecophysiological implications such as the heat transfers between the body and the surrounding environment when basking (seen in crocodilians) as well as in bone respiratory acidosis buffering during prolonged apnea (seen in both crocodilians and turtles). These ecophysiological functions rely on the set-up of a blood vessel network within and straight above the dermal bones.

References

Vertebrate anatomy Dermal and subcutaneous growths Armour (zoology) {{Vertebrate anatomy-stub