The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the

branchial arches Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arc ...

, or gill arches. In the

human embryo Human embryonic development, or human embryogenesis, is the development and formation of the human embryo. It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of d ...

, the arches are first seen during the fourth week of

development Development or developing may refer to: Arts *Development hell, when a project is stuck in development *Filmmaking, development phase, including finance and budgeting *Development (music), the process thematic material is reshaped *Photographi ...

. They appear as a series of outpouchings of mesoderm on both sides of the developing pharynx. The vasculature of the pharyngeal arches is known as the

aortic arches The aortic arches or pharyngeal arch arteries (previously referred to as branchial arches in human embryos) are a series of six paired embryological vascular structures which give rise to the great arteries of the neck and head. They are ventral ...

. In fish, the branchial arches support the gills.

Structure

In vertebrates, the pharyngeal arches are derived from all three

germ layers A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals that are sister taxa to the sponges) produce two or three prim ...

(the primary layers of cells that form during embryogenesis).

Neural crest cells Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, Per ...

enter these arches where they contribute to features of the skull and

facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull. The remainder of the skull is the braincase. In human anatomy and development, the facial skeleton is sometimes called the ''membranous viscerocr ...

such as bone and cartilage. However, the existence of pharyngeal structures before neural crest cells evolved is indicated by the existence of neural crest-independent mechanisms of pharyngeal arch development. The first, most anterior

pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arch ...

gives rise to the oral jaw. The second arch becomes the

hyoid The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical vertebra ...

and jaw support. In fish, the other posterior arches contribute to the branchial skeleton, which support the gills; in tetrapods the anterior arches develop into components of the ear, tonsils, and thymus. The genetic and developmental basis of pharyngeal arch development is well characterized. It has been shown that Hox genes and other developmental genes such as ''

DLX The DLX (pronounced "Deluxe") is a RISC processor architecture designed by John L. Hennessy and David A. Patterson, the principal designers of the Stanford MIPS and the Berkeley RISC designs (respectively), the two benchmark examples of RISC des ...

'' are important for patterning the anterior/posterior and dorsal/ventral axes of the branchial arches. Some fish species have a second set of jaws in their throat, known as pharyngeal jaws, which develop using the same genetic pathways involved in oral jaw formation. During human and all vertebrate

, a series of pharyngeal arch pairs form in the developing embryo. These project forward from the back of the embryo toward the front of the face and neck. Each arch develops its own artery, nerve that controls a distinct muscle group, and skeletal tissue. The arches are numbered from 1 to 6, with 1 being the arch closest to the head of the embryo, and arch 5 existing only transiently. These grow and join in the ventral midline. The first arch, as the first to form, separates the mouth pit or stomodeum from the pericardium. By differential growth the neck elongates and new arches form, so the pharynx has six arches ultimately. Each pharyngeal arch has a

cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and ...

stick, a muscle component that differentiates from the cartilaginous tissue, an artery, and a

cranial nerve Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...

. Each of these is surrounded by

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every ...

. Arches do not develop simultaneously but instead possess a "staggered" development. Pharyngeal pouches form on the

endodermal Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gastru ...

side between the arches, and

pharyngeal groove A pharyngeal groove (or branchial groove, or pharyngeal cleft) is made up of ectoderm unlike its counterpart the pharyngeal pouch on the endodermal side. The first pharyngeal groove produces the external auditory meatus (ear canal). The rest (2, ...

s (or clefts) form from the lateral

ectodermal The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from the o ...

surface of the

neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

region to separate the arches. In fish the pouches line up with the clefts, and these thin segments become gills. In mammals the

endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gastru ...

and ectoderm not only remain intact but also continue to be separated by a mesoderm layer. The development of the pharyngeal arches provides a useful landmark with which to establish the precise stage of embryonic development. Their formation and development corresponds to Carnegie stages 10 to 16 in mammals, and

Hamburger–Hamilton stages In developmental biology, the Hamburger–Hamilton stages (HH) are a series of 46 chronological stages in chick development, starting from laying of the egg and ending with a newly hatched chick. It is named for its creators, Viktor Hamburger an ...

14 to 28 in the chicken. Although there are six pharyngeal arches, in humans the fifth arch exists only transiently during embryogenesis.

First arch

The first pharyngeal arch also mandibular arch (corresponding to the first branchial arch or gill arch of fish), is the first of six pharyngeal arches that develops during the fourth week of

.William J. Larsen (2001). Human embryology. Edinburgh: Churchill Livingstone. It is located between the stomodeum and the first pharyngeal groove.

Processes

This arch divides into a maxillary process and a mandibular process, giving rise to structures including the bones of the lower two-thirds of the face and the jaw. The maxillary process becomes the maxilla (or upper jaw, although there are large differences among animals), and

palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sepa ...

while the mandibular process becomes the

mandible 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 tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

or lower jaw. This arch also gives rise to the

muscles of mastication There are four classical muscles of mastication. During mastication, three muscles of mastication (''musculi masticatorii'') are responsible for adduction of the jaw, and one (the lateral pterygoid) helps to abduct it. All four move the jaw late ...

Meckel's cartilage

Meckel's cartilage In humans, the cartilaginous bar of the mandibular arch is formed by what are known as Meckel's cartilages (right and left) also known as Meckelian cartilages; above this the incus and malleus are developed. Meckel's cartilage arises from the firs ...

forms in the mesoderm of the mandibular process and eventually regresses to form the incus and

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 fr ...

of the

middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the ...

, the anterior ligament of the malleus and the sphenomandibular ligament. The

or lower jaw forms by perichondral ossification using Meckel's cartilage as a 'template', but the maxillary does ''not'' arise from direct ossification of Meckel's cartilage.

Derivatives

The skeletal elements and muscles are derived from mesoderm of the pharyngeal arches. Skeletal *

and incus of the

* maxilla and

spine of sphenoid bone The sphenoidal spine (Latin: "''spina angularis''") is a downwardly directed process at the apex of the great wings of the sphenoid bone that serves as the origin of the sphenomandibular ligament. Additional images File:Spine of sphenoid bone. ...

* sphenomandibular ligament * palatine bone *

squamous part of temporal bone The squamous part of temporal bone, or temporal squama, forms the front and upper part of the temporal bone, and is scale-like, thin, and translucent. Surfaces Its outer surface is smooth and convex; it affords attachment to the temporal muscle ...

anterior ligament of malleus The ligaments of malleus are three ligaments that attach the malleus in the middle ear. They are the anterior, lateral and superior ligaments. The anterior ligament of the malleus also known as Casserio's ligament is a fibrous band that extends ...

Muscles *

(chewing) **

masseter In human anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it ...

** medial and lateral pterygoid muscles **

temporalis In anatomy, the temporalis muscle, also known as the temporal muscle, is one of the muscles of mastication (chewing). It is a broad, fan-shaped convergent muscle on each side of the head that fills the temporal fossa, superior to the zygomatic ...

* mylohyoid muscle *

digastric muscle The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle bellie ...

, anterior belly * tensor veli palatini muscle *

tensor tympani muscle The tensor tympani is a muscle within the middle ear, located in the bony canal above the bony part of the auditory tube, and connects to the malleus bone. Its role is to dampen loud sounds, such as those produced from chewing, shouting, or thun ...

Other

Mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...

and glands of the anterior two thirds of the tongue are derived from ectoderm and

of the arch.

Nerve supply

The mandibular and maxillary branches of the trigeminal nerve (CN V) innervate the structures derived from the corresponding processes of the first arch. In some lower animals, each arch is supplied by two cranial nerves. The nerve of the arch itself runs along the cranial side of the arch and is called post-trematic nerve of the arch. Each arch also receives a branch from the nerve of the succeeding arch called the pre-trematic nerve which runs along the caudal border of the arch. In human embryo, a double innervation is seen only in the first pharyngeal arch. The mandibular nerve is the post-trematic nerve of the first arch and

chorda tympani The chorda tympani is a branch of the facial nerve that originates from the taste buds in the front of the tongue, runs through the middle ear, and carries taste messages to the brain. It joins the facial nerve (cranial nerve VII) inside the faci ...

(branch of facial nerve) is the pre-trematic nerve. This double innervation is reflected in the nerve supply of anterior two-thirds of

tongue The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste b ...

which is derived from the first arch.

Blood supply

The artery of the first arch is the first

aortic arch The aortic arch, arch of the aorta, or transverse aortic arch () is the part of the aorta between the ascending and descending aorta. The arch travels backward, so that it ultimately runs to the left of the trachea. Structure The aorta begins a ...

,McMinn, R., 1994. ''Last's anatomy: Regional and applied (9th ed).'' which partially persists as the maxillary artery.

Second arch

The second pharyngeal arch or hyoid arch, is the second of fifth pharyngeal arches that develops in fetal life during the fourth week of development and assists in forming the side and front of the

Reichert's cartilage

Cartilage in the second pharyngeal arch is referred to as Reichert's cartilage and contributes to many structures in the fully developed adult. In contrast to the

of the first pharyngeal arch it does not constitute a continuous element, and instead is composed of two distinct cartilaginous segments joined by a faint layer of

. Dorsal ends of Reichert's cartilage ossify during development to form the stapes of the

before being incorporated into the middle ear cavity, while the ventral portion ossifies to form the lesser cornu and upper part of the body of the

hyoid bone The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical ver ...

. Caudal to what will eventually become the stapes, Reichert's cartilage also forms the styloid process of the

temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples, and house the structures of the ears. T ...

. The cartilage between the

and styloid process will not remain as development continues, but its

perichondrium The perichondrium (from Greek el, περί, peri, around, label=none and el, χόνδρος, chondros, cartilage, label=none) is a layer of dense irregular connective tissue that surrounds the cartilage of developing bone. It consists of two s ...

will eventually form the

stylohyoid ligament The stylohyoid ligament is a ligament that connects the hyoid bone to the temporal styloid process (of the temporal bone of the skull). Structure The stylohyoid ligament connects the lesser horn of hyoid bone to the styloid process of the t ...

Derivatives

Skeletal From the cartilage of the second arch arises * Stapes, *

Temporal styloid process The temporal styloid process is a slender bony process of the temporal bone extending downward and forward from the undersurface of the temporal bone just below the ear. The styloid process gives attachments to several muscles, and ligaments. Stru ...

, *

Stylohyoid ligament The stylohyoid ligament is a ligament that connects the hyoid bone to the temporal styloid process (of the temporal bone of the skull). Structure The stylohyoid ligament connects the lesser horn of hyoid bone to the styloid process of the t ...

, and *

Lesser cornu The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical vertebra ...

of the

. Muscles *

Facial muscles The facial muscles are a group of striated skeletal muscles supplied by the facial nerve (cranial nerve VII) that, among other things, control facial expression. These muscles are also called mimetic muscles. They are only found in mammals, a ...

* Occipitofrontalis muscle * Platysma *

Stylohyoid The stylohyoid muscle is a slender muscle, lying anterior and superior of the posterior belly of the digastric muscle. It is one of the suprahyoid muscles. It shares this muscle's innervation by the facial nerve, and functions to draw the hyoid ...

muscle *Posterior belly of

Stapedius The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes or strirrup bone of the middle ear. Structure The stapedius emerges fr ...

muscle *Auricular muscles

Nerve supply

Facial nerve (CN VII)

Blood supply

The artery of the second arch is the second

, which gives origin to the stapedial artery in some mammals but atrophies in humans.

Muscles derived from the pharyngeal arches

Pharyngeal muscles or Branchial muscles are striated muscles of the head and neck. Unlike skeletal muscles that developmentally come from

somites The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide in ...

, pharyngeal muscles are developmentally formed from the pharyngeal arches. Most of the skeletal musculature supplied by the cranial nerves (

special visceral efferent Special visceral efferent fibers (SVE) are the efferent nerve fibers that provide motor innervation to the muscles of the pharyngeal arches in humans, and the branchial arches in fish. Some sources prefer the term "branchiomotor" or "branchial eff ...

) is pharyngeal. Exceptions include, but are not limited to, the

extraocular muscles The extraocular muscles (extrinsic ocular muscles), are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the oth ...

and some of the muscles of the tongue. These exceptions receive general somatic efferent innervation.

First arch

All of the pharyngeal muscles that come from the first pharyngeal arch are innervated by the mandibular divisions of the trigeminal nerve. These muscles include all the

, the anterior belly of the

digastric The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle bellie ...

, the mylohyoid, tensor tympani, and tensor veli palatini.

Second arch

All of the pharyngeal muscles of the second pharyngeal arch are innervated by the facial nerve. These muscles include the muscles of facial expression, the posterior belly of the

, the

stylohyoid The stylohyoid muscle is a slender muscle, lying anterior and superior of the posterior belly of the digastric muscle. It is one of the suprahyoid muscles. It shares this muscle's innervation by the facial nerve, and functions to draw the hyoid ...

muscle, the auricular muscle and the

stapedius The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes or strirrup bone of the middle ear. Structure The stapedius emerges fr ...

muscle of the middle ear.

Third arch

There is only one muscle of the third pharyngeal arch, the stylopharyngeus. The stylopharyngeus and other structures from the third pharyngeal arch are all innervated by the

glossopharyngeal nerve The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior (closer to the nose) to the vagus nerve. Bei ...

Fourth and sixth arches

All the pharyngeal muscles of the fourth and sixth arches are innervated by the superior laryngeal and the recurrent laryngeal branches of the vagus nerve. These muscles include all the muscles of the palate (exception of the tensor veli palatini which is innervated by the trigeminal nerve), all the muscles of the pharynx (except stylopharyngeus which is innervated by the

), and all the muscles of the larynx.

In humans

Amniotes have five arches, numbered 1 to 5. Older literature reports the fifth arch as the sixth arch, the fifth being absent. More is known about the fate of the first arch than the remaining four. The first three contribute to structures above the larynx, whereas the last two contribute to the larynx and trachea. The recurrent laryngeal nerves are produced from the nerve of arch 5, and the laryngeal cartilages from arches 4 and 5. The superior laryngeal branch of the vagus nerve arises from arch 4. Its arteries, which project between the nerves of the fourth and fifth arches, become the left-side arch of the aorta and the right subclavian artery. On the right side, the artery of arch 5 is obliterated while, on the left side, the artery persists as the

ductus arteriosus The ''ductus arteriosus'', also called the ''ductus Botalli'', named after the Italian physiologist Leonardo Botallo, is a blood vessel in the developing fetus connecting the trunk of the pulmonary artery to the proximal descending aorta. It all ...

; circulatory changes immediately following birth cause the vessel to close down, leaving a remnant, the

ligamentum arteriosum The ligamentum arteriosum (arterial ligament), also known as the Ligament of Botallo or Harvey's ligament, is a small ligament attaching the aorta to the pulmonary artery. It serves no function in adults but is the remnant of the ductus arteriosus ...

. During growth, these arteries descend into their ultimate positions in the chest, creating the elongated recurrent paths.

References

External links

* {{Authority control Vertebrate anatomy Pharyngeal arches Animal developmental biology

Structure

First arch

Processes

Meckel's cartilage

Derivatives

Nerve supply

Blood supply

Second arch

Reichert's cartilage

Derivatives

Nerve supply

Blood supply

Muscles derived from the pharyngeal arches

First arch

Second arch

Third arch

Fourth and sixth arches

In humans

See also

References

External links