The anterior external arcuate fibers (ventral external arcuate fibers) vary as to their prominence in different cases: in some they form an almost continuous layer covering the pyramid (brain stem)

Pyramid

A pyramid is a structure whose outer surfaces are triangular and converge at a single point. The base of a pyramid can be trilateral, quadrilateral, or any polygon shape, meaning that a pyramid has at least three triangular surfaces...

 and olivary body

Olive

The olive , Olea europaea), is a species of a small tree in the family Oleaceae, native to the coastal areas of the eastern Mediterranean Basin as well as northern Iran at the south end of the Caspian Sea.Its fruit, also called the olive, is of major agricultural importance in the...

, while in others they are barely visible on the surface.

They arise from the cells of the gracile

Gracile

The English word "gracile" means slender. It derives from the Latin adjective gracilis , or gracile which in either form means slender, and when transferred for example to discourse, takes the sense of "without ornament", "simple", or various similar connotations.In his famous "Glossary of Botanic...

 and cuneate

Cuneate

Cuneate means "wedge-shaped," it can apply to:*cuneate leaf, a leaf shape*the cuneate nucleus, a part of the brainstem*the cuneate fasciculus, a tract from the spinal cord into the brainstem...

 nuclei, and passing forward through the formatio reticularis, decussate in the middle line.

Most of them reach the surface by way of the anterior median fissure

Anterior median fissure

Anterior median fissure can refer to:* Anterior median fissure of the spinal cord* Anterior median fissure of the medulla oblongata...

, and arch backward over the pyramid.

Reinforced by others which emerge between the pyramid and olive, they pass backward over the olive and lateral district of the medulla oblongata

Medulla oblongata

The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...

, and enter the inferior peduncle.

They thus connect the cerebellum

Cerebellum

The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...

 with the gracile and cuneate nuclei of the opposite side.

As the fibers arch across the pyramid, they enclose a small nucleus which lies in front of and medial to the pyramid.

This is named the nucleus arcuatus, and is serially continuous above with the nuclei pontis in the pons

Pons

The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...

; it contains small fusiform cells, around which some of the arcuate fibers end, and from which others arise.