In the developing vertebrate

Vertebrate

Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

 embryo

Embryo

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

, the somitomeres (or somatomeres) are loose masses of paraxial mesoderm

Paraxial mesoderm

Paraxial mesoderm is the area of mesoderm that forms just lateral to the neural tube on both sides.It differentiates rostrally into somatomeres and caudally into somites.It gives rise to the somitomeres/somites and mesoderm of the branchial arches....

 derived cells

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

 that form along each side of the neural tube

Neural tube

In the developing vertebrate, the neural tube is the embryo's precursor to the central nervous system, which comprises the brain and spinal cord...

 towards the end of the third gestation

Gestation

Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....

al week. The approximately 50 pairs of somitomeres begin developing in the cranial (head) region, continuing in a caudal (tail) direction until the end of week four.

Development

The first seven somitomeres give rise to the striated muscles of the face

Face

The face is a central sense organ complex, for those animals that have one, normally on the ventral surface of the head, and can, depending on the definition in the human case, include the hair, forehead, eyebrow, eyelashes, eyes, nose, ears, cheeks, mouth, lips, philtrum, temple, teeth, skin, and...

, jaw

Jaw

The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...

s, and throat

Throat

In vertebrate anatomy, the throat is the anterior part of the neck, in front of the vertebral column. It consists of the pharynx and larynx...

.

The remaining somitomeres, likely driven by periodic expression of the hairy gene, begin expressing adhesion proteins such as N-cadherin

Cadherin

Cadherins are a class of type-1 transmembrane proteins. They play important roles in cell adhesion, ensuring that cells within tissues are bound together. They are dependent on calcium ions to function, hence their name.The cadherin superfamily includes cadherins, protocadherins, desmogleins, and...

 and fibronectin

Fibronectin

Fibronectin is a high-molecular weight glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. In addition to integrins, fibronectin also binds extracellular matrix components such as collagen, fibrin and heparan sulfate proteoglycans...

, compact, and bud off forming somite

Somite

A somite is a division of the body of an animal. In vertebrates this is mainly discernible in the embryo stage; in arthropods it is a characteristic of a hypothetical ancestor.- In vertebrates :...

s. The somites give rise to the vertebral column

Vertebral column

In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

 (sclerotome

Sclerotome

A sclerotome is part of a somite, a structure in vertebrate embryonic development. Sclerotomes eventually differentiate into the vertebrae and most of the skull...

), associated muscles (myotome

Myotome

In vertebrate embryonic development, a myotome is a group of tissues formed from somites that develop into the body wall muscle.Each myotome divides into a dorsal epaxial part and a ventral hypaxial part....

), and overlying dermis (dermatome

Dermatome

Dermatome may refer to:*Dermatome , a surgical instrument used to produce thin slices of skin*Dermatome , an area of skin that is supplied by a single pair of dorsal roots*Dermatome...

).
There are a total of 37 somite pairs at the end of the fifth week of development, after the first occipital somite and 5-7 coccygeal somites disappear from the original 42-44 somites