GENERAL STRUCTURE OF THE BODY. 



31 



are some large serous cavities, such as the abdomen, 

 that may be considered as extended lymph spaces. 



The lymphatic vessels have delicate, transparent walls, 

 with three coats like the arteries, though much thinner, 

 and anastomose even more freely than the veins. They 

 have a beaded appearance due to the presence of numer- 



a.l. 



FIG. 8. Diagram of a lymphatic gland, showing afferent (a. Z.) and efferent 

 (e. Z.) lymphatic vessels; cortical substance (C); medullary substance (M)\ fi- 

 brous coat (c) ; sending trabeculse (tr) into the substance of the gland, where they 

 branch, and in the medullary part form a reticulum; the trabeculse are sur- 

 rounded by the lymph path or sinus (Z. s.), which separates them from the 

 adenoid tissue (Z. h.). (Sharpey.) 



ous valves, which form constrictions on their surface. 

 The right lymphatic duct, which is only about an 

 inch long, drains all the lymphatics of the right half of 

 the upper part of the trunk, the head, and the neck ap- 

 proximately, while the thoracic duct drains those of the 

 rest of the body. The latter, which is the largest vessel 

 of the system, begins opposite the second lumbar ver- 



