The anterior median fissure (ventral or ventromedian fissure) contains a fold of
pia mater
Pia mater ( or ),Entry "pia mater" in medulla oblongata: It ends at the lower border of the pons in a small triangular expansion, termed the foramen cecum.
Its lower part is interrupted by bundles of fibers that cross obliquely from one side to the other, and constitute the
pyramidal decussation
In neuroanatomy, the medullary pyramids are paired white matter structures of the brainstem's medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts. The lower limit ...
.
Some fibers, termed the
anterior external arcuate fibers
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
, emerge from the fissure above this decussation and curve lateralward and upward over the surface of the medulla oblongata to join the
inferior peduncle
The upper part of the posterior district of the medulla oblongata is occupied by the inferior cerebellar peduncle, a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerv ...
.
Additional images
File:Gray679.png, Medulla oblongata and pons. Anterior surface.
File:Gray699.png, Diagram showing the course of the arcuate fibers.
File:Gray700.png, The reticular formation of the medulla oblongata, shown by a transverse section passing through the middle of the olive.