| Anterior external arcuate fibers |
| Anterior external arcuate fibers | |
| Latin: | fibrae arcuatae externae anteriores |
The anterior external arcuate fibers (ventral external arcuate fibers) vary as to their prominence: in some cases they form an almost continuous layer covering the medullary pyramids and olivary body, while in other cases they are barely visible on the surface.
They arise from the cells of the gracile and cuneate nuclei, and pass forward through the reticular formation to decussate (cross over to the other side) in the middle line.
Most of them reach the surface by way of the anterior median fissure, and arch backward over the pyramid, the olive, and the lateral district of the medulla oblongata to enter the cerebellum through the inferior peduncle. The fibers are reinforced in their course by fibers emerging between the pyramid and olive.
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 arcuate nucleus, and is serially continuous above with the pontine nuclei in the pons; it contains small fusiform (spindle-shaped) cells, around which some of the arcuate fibers end, and from which others arise.