(From duco, to lead). A duct or canal; a word frequently applied to parts of the body through which particular fluids are conveyed.

Ductus arteriosus. It is found only in the foetus, and very young children, arising from the aorta de-scendens, immediately below the left subclavian artery. In adults it is closed up, and appears like a short ligament adhering by one end to the aorta, and by the other to the pulmonary artery; so that, in reality, it deserves no other name than that of ligamentum arteriosum.

Ductus auris palatinus. See Tuba Eusta-chiana.

Ductus ad nasum. See Antrum genae.

Ductus biliaris, and Ductus communis chole-dochus. See Jecur.

Ductus lactiferi. The excretory ducts from the glans of the breast, which convey the milk to the nipple.

Ductus nigri. On separating the crystalline and vitreous humours from their adhesions to the ciliary processes, part of the black pigment, on the choroides, is left in black radiated lines, which are thus named.

Ductus pancreatis opens into the duodenum, near, or often at, an aperture common to it and the ductus communis choledochus.

Ductus salivalis. See Saliva. Ductus stenonis. See Salivalis ductus ste-nonis.

Ductus thoracicus. Thoracic duct. Pecquet discovered and demonstrated it at Paris, 1615, 1652. It is a thin transparent canal, which runs up from the receptaculum chyli, along the spina dorsi, between the vena azygos and aorta, often above the fifth vertebra of the back; from thence it passes behind the aorta, towards the left side, and ascends behind the left subclavian vein, where it terminates in some subjects by a kind of vesicula; in others by several branches united together, and opens into the back side of the subclavian vein near the outside of the internal jugular. It is furnished with many semilunar valves directed upwards, to prevent regurgitation. Its opening into the subclavian vein in the human body is, in the place of valves, covered by several pelliculae, so disposed as to admit only the gradual entrance of the chyle into the vein, and hinder the blood from running into the duct. It is sometimes double, one lying on each side; and sometimes it is accompanied with appendices,called pampini-formes. Any compression upon this duct will occasion atrophy, and death; as it prevents the fluids by which the animal is to be nourished from entering the course of circulation. See Monro's Osteology.

Ductus venosus. When the vena cava passes the liver, in the foetus, it sends off the ductus venosus, which communicates with the sinus of the vena portae; but in the adults becomes a flat ligament.

Ductus Whartoni From -Wharton the discoverer. The inferior salival duct is thus named from his describing it.