A ^ D PHYSIOLOGY. 



2S5 



Fig. 2*7. 



size, of a knotted appearance, and very frequently dividing into 

 two nearly equal branches. Like veins and arteries, they have 

 three coats, with folds of the 

 inner coat for the formation 

 of valves, giving them a knot- 

 ted appearance. They com- 

 mence in a minute net-work 

 in nearly every organ of the 

 body, and soon unite into a 

 few large trunks which take 

 a direction towards the veins 

 in the lower part of the neck. 

 This net-work is so exceed- 

 ingly delicate, that when filled 

 with mercury it presents the 

 appearance of a sheet of silver. 

 The necessity of such an im- 

 mense number of these vessels 

 arises from the constant lib- 

 eration of the waste particles 

 of matter which need to be 

 removed as soon as possible, 

 that the deposition of new 

 particles may not be prevented. 



501. Lymphatic Glands. — 



As the minute lymphatics 

 unite into larger trunks, they A Yiew of the Eight Lymphatic The 



racic Duct. 1, Arch of the Aorta. 2, 

 Thoracic Aorta. 3, Abdominal Aorta. 4, Arteria Innominata. 5, Left Carotid. 6, 

 Left Sub-Clavian. 7, Superior Cava. 8, The two Verne Innominate. 9, The Internal 

 Jugular and Sub-Clavian Vein at each side. 10, The Vena Azygos. 11, The Termination 

 of the Vena Hemi-Azygos in the Vena Azygos. 12, The Receptaculum Chyli : several 

 Lymphatic Trunks are seen opening into it. 13, The Thoracic Duct dividing, opposite 

 the Middle Dorsal Vertebra, into two branches, which soon re-unite ; the course of the 

 Duct behind the Arch of the Aorta and Left Sub-Clavian Artery is shown by a dotted 

 Line. 14. The Duct making its turn at the Root of the Neck and receiving several Lym- 

 phatic Trunks previous to terminating in the Posterior Angle of the Junction of the In- 

 ternal Jugular and Sub-Clavian Veins. 15, The Termination of the Trunk of the Lym- 

 phatics of the Upper Extremity. 



500. Describe the lymphatics. How many coats have they ? What is said of the net- 

 work which they make ? Why the necessity of such a multitude ? 



