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In humans, the cartilaginous bar of the
mandibular arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryogenesis, embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, ...
is formed by what are known as Meckel's cartilages (right and left) also known as Meckelian cartilages; above this the
incus The ''incus'' or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The ''incus'' receives vibrations from the ''malleus'', to which it is connected laterally, and transmits these to the ''s ...
and
malleus The malleus, or hammer, is a hammer-shaped small bone or ossicle The ossicles (also called auditory ossicles) are three bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. ...

malleus
are developed. Meckel's cartilage arises from the first
pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the Animal embryonic development, embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the br ...
. The dorsal end of each cartilage is connected with the ear-capsule and is ossified to form the
malleus The malleus, or hammer, is a hammer-shaped small bone or ossicle The ossicles (also called auditory ossicles) are three bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. ...

malleus
; the ventral ends meet each other in the region of the
symphysis menti In human anatomy, the facial skeleton of the skull the external surface of the Human mandible, mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two ...
, and are usually regarded as undergoing
ossification Image:Bonemetabolism.svg, 300 px, Bone is broken down by osteoclasts, and rebuilt by osteoblasts, both of which communicate through cytokine (TGF-β, Insulin-like growth factor, IGF) signalling. Ossification (or osteogenesis) in bone remodeling ...
to form that portion of the
mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...

mandible
which contains the
incisor teeth Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whereas ...
. The intervening part of the cartilage disappears; the portion immediately adjacent to the malleus is replaced by fibrous membrane, which constitutes the
sphenomandibular ligament The sphenomandibular ligament (internal lateral ligament) is a flat, thin band which is attached superiorly to the spina angularis (spine) of the sphenoid bone, and, becoming broader as it descends, is fixed to the Lingula of mandible, lingula of th ...
, while from the connective tissue covering the remainder of the cartilage the greater part of the mandible is ossified.
Johann Friedrich Meckel, the Younger
Johann Friedrich Meckel, the Younger
discovered this cartilage in 1820.


Evolution

The Meckelian Cartilage, also known as "Meckel's Cartilage", is a piece of
cartilage Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue Elastic is a word often used to describe or identify certain types of elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-m ...

cartilage
from which the mandibles (lower jaws) of
vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...

vertebrates
evolved. Originally it was the lower of two cartilages which supported the first
branchial arch Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills A gill () is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen Oxygen is the chemical element wit ...
in early
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
. Then it grew longer and stronger, and acquired muscles capable of closing the developing jaw.The Gill Arches: Meckel's Cartilage
''
palaeos Palaeos.com is a web site on biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, ...
''. Retrieved 4 December 2014.
In early fish and in
chondrichthyans Chondrichthyes (; from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10 ...
(cartilaginous fish such as
shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified withi ...

shark
s), the Meckelian Cartilage continued to be the main component of the lower jaw. But in the adult forms of
osteichthyans
osteichthyans
(bony fish) and their descendants (
amphibians Amphibians are ectotherm File:Junonia lemonias DSF by Kadavoor.JPG, ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτός (''ektós'') "outside" and θερμός (''thermós'') "hot") is an ...

amphibians
,
reptiles Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptiles
(including
birds Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

birds
),
mammals Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the R ...
), the cartilage was covered in bone – although in their
embryos An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...
the jaw initially develops as the Meckelian Cartilage. In all
tetrapods Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...

tetrapods
the cartilage partially ossifies (changes to bone) at the rear end of the jaw and becomes the
articular The articular bone is part of the lower jaw of most vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Anima ...
bone, which forms part of the jaw joint in all tetrapods except
mammals Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the R ...
. In some extinct mammal groups like
eutriconodont Eutriconodonta is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste ...
s, the Meckel's cartilage still connected otherwise entirely modern ear bones to the jaw.


Additional images

File:Gray1011.png, Vertical section of the mandible of an early human fetus. X 25.


References


External links

* {{Authority control
Skeletal system {{Commons cat, Skeletal system A skeleton (endoskeleton) is made up of bones. ''See also:'' :Bone products Musculoskeletal system ...
Pharyngeal arches