Ultrastructure of the monkey thoracic duct and the cisterna chyli

The ultrastructure of the thoracic duct and cisterna chyli was studied in the Formosan rock monkey. This duct is approximately 40% of the crown-rump length. Bicuspid valves ensure one-way drainage of the lymph and prevent reflux of lymph. Ultrastructural variations between the 2 sides of the valves and the functional significance of the different types of valve are discussed. The muscular organisation in the tunica media is similar to that of the human thoracic duct. The abdominal and thoracic parts of the duct contain smooth muscle and probably exhibit active peristalsis, while the cervical part is less muscular and functions like a vein.