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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 and postcranial structures. In bony fish, dermal bone is found in the fin rays and scales. A special example of dermal bone is the clavicle. Some of the dermal bone functions regard ...
There are two principal types of bones: Dermal bone is directly formed in the dermis (skin), usually growing from initially thin plates. Among others, most bones forming the outer surface of the skull and lower jaws are dermal bones. In contrast, endochondral bone is formed from a cartilaginous precursor, which ossifies (turn into bone). [1 ...
Indirect fracture healing, the most common type of bone repair, [10] relies heavily on endochondral ossification. In this type of healing, endochondral ossification occurs within the fracture gap and external to the periosteum. In contrast, intramembranous ossification takes place directly beneath the periosteum, adjacent to the broken bone’s ...
The dermal bones gradually evolved into a fixed unit overlaying the endocranium like a heavy "lid", protecting the animal's head and brain from above. A more or less full shield of fused dermal bones was common in early bony fishes of the Devonian , and particularly well developed in shallow water species.
The dermatocranium is the portion of the cranium that is composed of dermal bone, as opposed to the endocranium and splanchnocranium, which are composed of endochondral bone. The dermatocranium comprises the skull roof, the facial skeleton (usually excluding the dentary), and—in fishes—the opercular bones. [1]
The facial skeleton comprises the facial bones that may attach to build a portion of the skull. [1] The remainder of the skull is the neurocranium.. In human anatomy and development, the facial skeleton is sometimes called the membranous viscerocranium, which comprises the mandible and dermatocranial elements that are not part of the braincase.
Minjinia turgenensis is a species of placoderm from the Devonian of Mongolia.It is known from a single specimen preserving part of the skull, including remains of endochondral bone, which indicates that a mineralised endoskeleton evolved before the split between bony and cartilaginous fish, and that it was lost in the latter group.
In other vertebrates, the foramen magnum is oriented towards the back, rather than downwards. The braincase contains a greater number of bones, most of which are endochondral rather than dermal: [8] The singular basioccipital is the rear lower part of the braincase, below the foramen magnum. It is homologous to the basilar part of the occipital ...