292 HAND-BOOK OF PHYSIOLOGY. 



teals and lymphatics. In some parts of their course all lymphatic vessels 

 pass through certain bodies called lymphatic glands. 



Lymphatic vessels are distributed in nearly all parts of the body. 

 Their existence, however, has not yet been determined in the placenta, the 

 umbilical cord, the membranes of the ovum, or in any of the non-vascular 

 parts, as the nails, cuticle, hair and the like. 



Lymphatics of head and I^IBWftRnMHiHKHIiBS! Lymphatics of head and 

 neck, right. BHBBgftflifggii KYffSB neck ' left 



Right internal jugular vein. Hflin! Thoracic duct. 



Right subclavian vein SWiMS 



E^feifc/ vB XfflSf&BK&n subclavian vein. 



Lymphatics of right arm. . 



Thoracic duct. 



Receptaculum chyli. 



Lacteals. 



Lymphatics of lower ex- m**T$& S aSS I Lymphatics of lower ex- 



tremities. S^5JtS9^9B;i^3H tremities. 



Q^BMliin&w^lBKKflOTlamiSBB 



FIG. 206. Diagram of the principal groups of lymphatic vessels (from Quain). 



Origin of Lymph Capillaries. The lymphatic capillaries com- 

 mence most commonly either in closely-meshed networks, or in irregular 

 lacunar spaces between the various structures of which the different 

 organs are composed. Such irregular spaces, forming what is now 

 termed the lymph-canalicular system, have been shown to exist in many 

 tissues. In serous membranes, such as the omentum and mesentery, they 

 occur as a connected system of very irregular branched spaces partly occu- 

 pied by connective-tissue corpuscles, and both in these and in many other 

 tissues are found to 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 



