230 THE LYMPHATIC SYSTEM 



3. By direct communication with the stomata of the serous mem- 

 branes. The presence of true stomata in the serous membranes of man 

 with the exception of possibly certain portions of the peritoneum is dis- 

 puted. 



The lymph is derived from the tissue juices and by absorption from 

 the alimentary tract, and is conveyed by the lymphatic capillaries to 



PIG. 238. LYMPHATIC CAPILLARY FROM THE SPERMATIC CORD OF A DOG, SHOWING 



NERVE ENDINGS. 



<a, nerve fibers. Methylene blue. Highly magnified. (After Kytmanof.) 



larger and larger lymph vessels, which resemble the small veins in their 

 structure, and which finally empty into the subclavian veins of the neck, 

 at their junction with the internal jugulars. 



The main lymph channels are the thoracic duct on the left, and the 

 right lymphatic duct. Only the thoracic duct drains the abdominal 

 lymphatics and is thus much the larger vessel. Toward its distal end 

 it expands into a receptacle for the absorbed chyle, the cisterna chyli. 



THE DEVELOPMENT OF LYMPH VESSELS 



According to Sabin the mammalian lymphatic system has its primary 

 origin in two paired and one unpaired venous sprouts : the jugular, inguinal 

 (sciatic), and mesenteric (retroperitoneal) lymph sacs. Certain investi- 

 gators (Huntington, Mem. Wistar Inst., 1911; McClure, Anat. Rec., 6, 6, 



