QUADRILATERAL

(Lat. quatuor, /owr, and lat us, aside.) In Geometry, a plane figure contained by four straight lines. It comprehends the square parallelogram, rectangle, rhombus, rhomboid, and trapezium. The most general properties of a quadrilateral figure are the two following: — l.The sum of the four angles is equal to four right angles; 2. The sum of the squares of the sides is equal to the sum of the squares of the two diagonals together, with four times the square of the straight line which joins the middle points of the diagonals. QUADRILATERALS, Quadrilatera. (Lat.) The name of a tribe of crabs (Brachyurous Crustaceans), comprehending those in which the carapace or shell is more or le square-shaped. QUAD RIPEN NATES, Quadnpennes. (Lat. quatuor, and penna, a wing.) The name of a section of An elytrous insects, including those which have four wings. [s. 1020]