224 



THE CIRCULATORY SYSTEM. 



[CH. XVIII. 



greater part of the contents of the lymphatic system of vessels 

 will be seen to pass through a comparatively large trunk called 



the thoracic duct, which finally 

 empties its contents into the blood- 

 stream, at the junction of the in- 

 ternal jugular and subclavian veins 

 of the left side. There is a smaller 

 duct on the right side. The lym- 

 phatic vessels of the intestinal canal 

 are called lacteals, because during 

 digestion the fluid contained in 

 them resembles milk in appearance ; 

 and the lymph in the lacteals during 

 the period of digestion is called chyle. 

 There is no distinction of struc- 

 ture, however, between lacteals and 

 lymphatics. In some parts of its 

 course the lymph-stream passes 

 through lymphatic glands, to be 

 desci'ibed later on. 



Origin of Lymph Capillaries. 

 The lymphatic capillaries commence 

 most commonly either (a) in closely- 

 meshed networks, or (6) in irregular 

 lacunar spaces between the various 

 structures of which the different 

 organs are composed. In serous 

 membranes such as the omentum 

 and mesentery they occur as a con- 

 nected system of very irregular 

 branched spaces partly occupied by 

 connective - tissue corpuscles, and 

 in these and other varieties of 

 connective tissue, the cell spaces 

 communicate freely with regular 

 lymphatic vessels. In many cases, 

 though they are formed mostly by 

 the chinks and crannies between the 

 blood vessels, secreting ducts, and 

 other parts which may happen to 

 form the framework of the organ 

 are lined by a distinct layer of 



Fig. 229. -Superficial lymphatics of 

 the forearm and palm of the hand, 

 i. 5. Two small glands at the bend 

 of the arm. 6. Radial lymphatic 

 vessels. 7. Ulnar lymphatic vessels. 



8, 8'. Palmar arch of lymphatics. 



9, 9 . Outer and inner sets of ves- 

 sels. 6. Cephalic vein. d. Radial 

 vein. e. Median vein. /. Ulnar 

 vein. The lymphatics are repre- 

 sented as lying on the deep fascia. 

 (Mascagni.) 



in which they exist, 

 endothelium. 



The lacteals offer an 'illustration of another mode of origin 



they 



