1) Below the margin 2) Submarginal 
• (a.) Below the margin; submarginal; as, an inframarginal convolution of the brain.
Inside of, as opposed to at, the margin. Example: for a firm that is producing 100 units, marginal cost is the cost of the 101st unit, while inframarginal cost is the cost of units 1,...,100.
Below any margin or edge. ... (05 Mar 2000) ... 
In`fra·mar'gin·al adjective [ Infra + marginal .] Below the margin; submarginal; as, an inframarginal convolution of the brain. 
Type: Term Pronunciation: in′fră-mar′ji-năl Definitions: 1. Below any margin or edge.
below the margin; submarginal.