Undermargin

In a valve of the type herein described, the combination of a valve casing provided with a partition dividing its interior into an inlet chamber, an outlet chamber and a piston chamber, the piston chamber having a lower portion of greater area than its upper portion, the said partition having a passage connecting the inlet and outlet chambers, the undermargin of said passage being formed into a valve seat, a restricted passage in the aforesaid partition connecting the inlet chamber with the lower end of the piston chamber, a piston valve disposed in said piston chamber and having upper and lower portions corresponding in diameter to that of the upper and lower portions of the piston chamber and moving therein, ....

Source: wiktionary

To overcome this difficulty, the undermargins of the poultice may be treated with Some oleaginous material such as petrolatum or one of the vegetable oils.

Source: wiktionary

The angle formed by the anterior and undermargins is termed the heel (A-5) by Hsu, the angulo anterior-inferior by Malogolowkin.

Source: wiktionary

This is performed through an incision along the undermargin of the breast, in the axilla, or at the border of the areola and the breast is then elevated and a pocket is formed between the breast and the chest wall.

Source: wiktionary