The flow of lymph from the tissues into the lymphatic collecting system. Lymph is formed from the tis¬ sue fluid that fills the interstitial spaces of the body. It is collected into lymph capillaries, which carry the lymph to the larger lymph vessels. These converge to form one of two main trunks, the right lymphatic duct and the thoracic duct. The right lymphatic duct drains the right side of the head, neck, and trunk and the right upper extremity; the thoracic duct drains the rest of the body. The thoracic duct originates at the cisterna chyli, which receives the lymphatics from the abdominal organs and legs. It courses upward through the diaphragm and thorax and empties into the left subclavian vein near its junction with the left interior jugular vein. The right lymphatic duct empties into the right subclavian vein. Along the course of lymph vessels are lymph nodes, which remove bacteria and other foreign materials, thus preventing their entrance into the bloodstream. Lymph flow is maintained by a difference in pressure at the two ends of the system. Important accessory factors aiding lymph flow are breathing movements and muscular activity.