The articular bone is part of the lower jaw of most

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, wi ...

, including most jawed fish,

amphibians Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arb ...

birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

and various kinds of

reptiles Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephali ...

, as well as ancestral

mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...

Anatomy

In most vertebrates, the articular bone is connected to two other lower jaw bones, the suprangular and the angular. Developmentally, it originates from the embryonic mandibular cartilage. The most caudal portion of the mandibular cartilage ossifies to form the articular bone, while the remainder of the mandibular cartilage either remains cartilaginous or disappears.

In snakes

snakes Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...

, the articular, surangular, and prearticular bones have fused to form the compound bone. The mandible is suspended from the quadrate bone and articulates at this compound bone.

Function

In amphibians and reptiles

In most tetrapods, the articular bone forms the lower portion of the jaw joint. The upper jaw articulates at the

quadrate bone The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms uppe ...

In mammals

, the articular bone evolves to form the

malleus The malleus, or hammer, is a hammer-shaped small bone or ossicle of the middle ear. It connects with the incus, and is attached to the inner surface of the eardrum. The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibrations ...

, one of the mammalian ossicles of the middle ear. This is an

apomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

of the mammalian clade, and is used to determine the fossil transition to mammals. It is

analogous Analogy (from Greek ''analogia'', "proportion", from ''ana-'' "upon, according to" lso "against", "anew"+ ''logos'' "ratio" lso "word, speech, reckoning" is a cognitive process of transferring information or meaning from a particular subject (th ...

to, but not

homologous Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor *Sequence homology, biological homology between DNA, RNA, or protein sequences * Homologous chrom ...

to the

articular process The articular processes or zygapophyses (Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = "process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vertebr ...

of the

lower jaw In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

. After the loss of the quadrate-articular joint, the squamosal and dentary bones form the new jaw joint in mammals.

References