Pentadatyl Limb. The kind of limb found in four classes of vertebrates : Amphibia, reptiles, birds, and mammals, collectively called the tetrapods. Evolved as an adaptation to life on land, and therefore not found in fishes or other primitively aquatic vertebrates.

The limb is characteristically in three parts : upper arm or thigh ; fore-arm or shank; hand or foot.
The latter bears five terminal fingers or toes (digits), hence the name pentadactyl. The first part contains one long bone (humerus in arm, femur in leg); the second two long more or less parallel bone (radius and ulna in arm, tibia and fibula in leg); the third many small bones in a fairly uniform pattern ( carpals, metacarpals, and phalanges successively in arm ; tarsal, metatarsals, and phalanges in leg). Many modifications of this fundamental pattern occur, through loss or fusion of elements, especially in the terminal parts.

Peptone. A Soluble product resulting from protein hydrolysis.

Perennation. The survival during unfavourable condition when the organism has a period of reduced activity.

Perfect.
1. When a flower which has both functional anthers and ovules.
2. Said of the stage in the life-cycle of a fungus which produces spores by sexual fusion.

Perfusion. The passage of a liquid through an organ or tissue.

Periandra. The ‘leaves’ surrounding a group of antheridia in mosses.