356 THE LYMPHATIC SYSTEM. 



cipal bloodvessels and nerves. Those of the lower extremities enter 

 the cavity of the abdomen, and join with the lymphatics of the abdo- 

 minal organs to form the commencement of the thoracic duct, which 

 ascends through the cavity of the chest, receiving branches from the 

 thoracic organs to the root of the neck, where it is joined by lymphatics 

 from the left side of the head and the left upper extremity, and ter- 

 minates in the left subclavian vein, at the point of its junction with the 

 left internal jugular. The lymphatics coming from the right side of 

 the head and neck, the right upper extremity, and a portion of the 

 thoracic organs, form a trunk of smaller size, the right lymphatic duct, 

 which terminates in the right subclavian vein at its junction with the 

 right internal jugular. Thus the lymph, collected from the vascular 

 tissues of the entire body, is mingled with the venous blood a short 

 distance before its arrival at the right side of the heart. 



The Great Serous Cavities of the Body are Lymphatic Lacunae. 

 It is well known that in the amphibious reptiles there are irregularly- 

 shaped spaces or lacunae, forming a part of the lymphatic system and 

 interposed between adjacent organs in various parts of the body. In 

 the mammalia the peritoneal and pleural cavities, and probably all the 

 principal serous sacs, are also in direct communication with the lym- 

 phatic vessels. This was first shown by Recklinghausen 1 for the peri- 

 toneal cavity of the rabbit, which communicates by microscopic orifices 

 with the lymphatic vessels in the central tendon of the diaphragm. 

 These communications were demonstrated in two ways : First, on in- 

 jecting into the peritoneal cavity of the animal milk, or a watery fluid 

 holding in suspension minute granules of coloring matter, the lymphatic 

 vessels of the central tendon of the diaphragm were afterward found to 

 be filled with the white or colored injection. Secondly, the central tendon 

 of the diaphragm being carefully removed from the recently killed animal, 

 and a drop of milk placed upon its peritoneal surface, the milk globules 

 could be directly observed under the microscope, running in converging 

 currents to certain points on the surface of the tendon and there pene- 

 trating into its lymphatic vessels. The cavity of the pleura has also 

 been found by similar means to communicate with the lymphatic vessels 

 in its neighborhood. The serous cavities accordingly are either exten- 

 sive lacunae, forming in some regions the origin of the lymphatic vessels, 

 or else they are wide but shallow expansions of the cavity of the lym- 

 phatics, situated at various points in their course. 



The Lymphatic Glands. During the passage of the lymphatic vessels 

 from the periphery toward the centre, they are repeatedly interrupted by 

 ovoid, glandular-like bodies, of a pale reddish color and somewhat firm 

 consistency, varying in size from about two to twenty millimetres in 

 their long diameter. They do not exist in fish and reptiles, but are 

 always present in birds and mammalia. As a rule, several lymphatic 

 vessels reach these bodies, coming in a direction from the periphery ; and 



1 Strieker's Manual of Histology, Buck's Edition. New York, 1872, p. 221. 



