Term: marginal cell

Definition: The marginal cells are the most superficially located and the smallest cells of the superior colliculus. Their 5-8 micrometers wide, ovoid cell bodies are interspersed among or just beneath the anteroposterior coursing fibers of the stratum zonale. They project one to five, but most commonly two, dendrites from the deeper portions of the cell body surface. These branch several times to form a dense arbor of dendritic processes that extend as much as 150 micrometers subjacent to the cell body and may radiate as much as 75 micrometers lateral to the cell body. The axon of a marginal cell resembles other local axons in that it has an extensive local distribution, has a fine caliber, and many branches, but no over-all direction (fig. 9). There are both en passant and terminal varicosities, suggesting both types of synaptic contact. Our material did not show any marginal cell axon extending below the zone of horizontal cells.