sinus Definition

cavity, hollow: such as

a narrow elongated tract extending from a focus of suppuration and serving for the discharge of pus

a cavity in the substance of a bone of the skull that usually communicates with the nostrils and contains air

a small mass of tissue that is embedded in the musculature of the right atrium of higher vertebrates and that originates the impulses stimulating the heartbeat

the rhythm of the heart produced by impulses from the sinus node

an enlarged pouch that adjoins the heart, is formed by the union of the large systemic veins, and is the passage through which venous blood enters the heart in lower vertebrates and in embryos of higher forms

a small but richly innervated arterial enlargement that is located near the point in the neck where either carotid artery divides to form its main branches and that functions in the regulation of heart rate and blood pressure

a venous channel that is derived from the sinus venosus, is continuous with the largest of the cardiac veins, receives most of the blood from the walls of the heart, and empties into the right atrium

the ventral part of the embryonic mammalian cloaca that is formed by the growth of a fold dividing the cloaca where the hindgut and allantois meet and that eventually forms the neck of the bladder and some parts of the urinary and reproductive systems

a rare urogenital abnormality in which the urethral and vaginal tracts open into a common channel and share a single opening