Odontoid (Gr. ὀδούς, a tooth, εἶδσ, shape). The name of the bony peg of the second vertebra, around which the first turns. Œsophagus. Literally, that which carries food. The tube leading from the throat to the stomach; the gullet. Olecranon (Gr. ὠλένη, the elbow, and κρανίον, the top of the head). A curved eminence at the upper and back part of the ulna. Olfactory (Lat. _olfacio_, to smell). Pertaining to the sense of smell. Optic (Gr. ὀπτεύω, to see). Pertaining to the sense of sight. Orbit (Lat. _orbis_, a circle). The bony socket or cavity in which the eyeball is situated. Organ (Lat. _organum_, an instrument or implement). A portion of the body having some special function or duty. Osmosis (Gr. ὠσμός, impulsion). Diffusion of liquids through membranes. Ossa Innominata, pl. of Os Innominatum (Lat.). “Unnamed bones.” The irregular bones of the pelvis, unnamed on account of their non-resemblance to any known object. Otoconia (Gr. οὖς, an ear, and κονία, dust). Minute crystals of lime in the vestibule of the ear; also known as _otoliths_. Palate (Lat. _palatum_, the palate). The roof of the mouth, consisting of the hard and soft palate. Palpitation (Lat. _palpitatio_, a frequent or throbbing motion). A violent and irregular beating of the heart. Papilla. The small elevations found on the skin and mucous membranes. Paralysis (Gr. παραλύω, to loosen; also, to disable). Loss of function, especially of motion or feeling. Palsy. Parasite. A plant or animal that grows or lives on another. Pelvis. Literally, a basin. The bony cavity at the lower part of the trunk. Pepsin (Gr. πέπτω, to digest). The active principle of the gastric juice. Pericardium (Gr. περί, about, and καρδία, heart). The sac enclosing the heart. Periosteum (Gr. περί, around, ὀστέον, a bone). A delicate fibrous membrane which invests the bones. Peristaltic Movements (Gr. περί, round, and στέλλω, to send). The slow, wave-like movements of the stomach and intestines. Peritoneum (Gr. περιτείνω, to stretch around). The investing membrane of the stomach, intestines, and other abdominal organs. Perspiration (Lat. _perspiro_, to breathe through). The sweat. Petrous (Gr. πέτρα, a rock). The name of the hard portion of the temporal bone, in which are situated the drum of the ear and labyrinth. Phalanges (Gr. φάλαγξ, a body of soldiers closely arranged in ranks and files). The bones of the fingers and toes. Pharynx (Gr. φάρμγξ, the throat). The cavity between the back of the mouth and the gullet. Physiology (Gr. φύσις, nature, and λόγος, a discourse). The science of the functions of living, organized beings. Pia Mater (Lat.). Literally, the tender mother; the innermost of the three coverings of the brain. It is thin and delicate; hence the name. Pinna (Lat. a feather or wing). External cartilaginous flap of the ear. Plasma (Gr. πλάσσω, to mould). Anything formed or moulded. The liquid part of the blood.