The frontonasal process, or frontonasal prominence is one of the five swellings that develop to form the face. The frontonasal process is unpaired, and the others are the paired

maxillary prominence Continuous with the dorsal end of the Pharyngeal arch#First arch, first pharyngeal arch, and growing forward from its cephalic border, is a triangular process, the maxillary prominence (or maxillary process), the Anatomical terms of location#Dors ...

s, and the paired

mandibular prominence The mandibular prominence, or mandibular process is an embryological structure which gives rise to the lower portion of the face. The mandible and lower lip derive from it. The mesenchymal cells within the mandibular prominence condense to form M ...

s. During the fourth week of

embryonic development In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm, sperm cell (spermat ...

, an area of thickened

ectoderm 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 ...

develops, on each side of the frontonasal process called the

nasal placode In embryology, the nasal placode (or olfactory placode) gives rise to the olfactory epithelium of the human nose, nose. Two nasal Neurogenic placode, placodes arise as thickened ectoderm from the frontonasal process. They give rise to the human n ...

s or olfactory placodes, and appear immediately under the

forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the rostral (forward-most) portion of the brain. The forebrain controls body temperature, reproductive functions, eating, sleeping, and the display of emotions. Ve ...

. By invagination these areas are converted into two nasal pits, which indent the frontonasal prominence and divide it into medial and lateral nasal processes.

Nasal processes

The medial nasal process (nasomedial) on the inner side of each nasal pit merge into the intermaxillary segment and form the

upper lip The lips are a horizontal pair of soft appendages attached to the jaws and are the most visible part of the mouth of many animals, including humans. Mammal lips are soft, movable and serve to facilitate the ingestion of food (e.g. sucklin ...

, crest, and tip of the

nose A nose is a sensory organ and respiratory structure in vertebrates. It consists of a nasal cavity inside the head, and an external nose on the face. The external nose houses the nostrils, or nares, a pair of tubes providing airflow through the ...

. The medial nasal processes merge with the maxillary prominences. The lateral nasal process from each side merge to form the alae of the

Clinical significance

Failure to fuse can cause a

cleft lip A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. A cleft palate occurs when the palate (the roof of the mouth) contains an opening into the nasal cavi ...

Genetics

There is some evidence that development involves

Sonic hedgehog Sonic hedgehog protein (SHH) is a major signaling molecule of embryonic development in humans and animals, encoded by the ''SHH'' gene. This signaling molecule is key in regulating embryonic morphogenesis in all animals. SHH controls organoge ...

and Fibroblast growth factor 8.

References

External links

*
Flash animation at indiana.edu
* Embryology {{developmental-biology-stub