810 CIRCULATORY SYSTEM, 



unites with the common trunk of the other two, a few lines 

 above its point of formation; on other occasions, the chyliferous 

 trunks join it in a confused manner by nine or ten distinct 

 channels. Sometimes an intricate plexus of several large trunks; 

 derived from the lumbar and mesenteric glands,' by the gradual 

 reduction of the number of meshes from the successive joining 

 of trunks; begins to assume, at the crura of the diaphragm, tbe 

 form of a solitary trunk, whi^h is the thoracic duct. The trunk 

 of the duct is also disposed to keep up the anastomosing plan, 

 even in the thorax; we hence see it sometimes dividing itself 

 into two or ttiree channels of equal size, which unite again af- 

 ter a shorter or longer distance, and perhaps in a little space 

 repeat the same arrangement: sometimes a small arm is sent 

 offj which runs along for an inch or two, and joins into the pa- 

 rent stream; sometimes spiral turns are adopted by the thoracic 

 duct, sometimes nodosities, or small pouches are formed on its 

 sides; sometimes it is dilated at intervals in its whole circumfe- 

 rence. Sometimes it splits into several channels at its termina- 

 tion ; one channel terminating in one vein and another in a con- 

 tiguous one, of the several trunks forming the vena innomi- 

 nata ; on other occasions, instead of entering into a venous 

 trunk of the left side, it goes into the corresponding one of the 

 right. 



Commonly, it is about the size of a large crow-quill, but some- 

 times as large as a goose-quill, or even still more voluminous, 

 seeming to be in a varicose state, of which Mr. Cruikshank 

 mentions an example where it was half an inch in diameter, and 

 took two pounds of mercury to fill it. There is generally a pair 

 of valve's at the termination of the thoracic duct, or if it be di- 

 vided into several streams there is a pair at the embouchure of 

 each, to keep the venous blood out of it. There are also valves 

 in its length, but they are not numerous, and vary in different 

 subjects. 



The thoracic duct, as stated, is the grand outlet for the lym- 

 phatics of the left side of the head and neck, of the left supe- 

 rior extremity, of the intercostal spaces, of the left side of the 

 thorax, of the viscera of the abdomen, and of the inferior ex- 

 tremities. Though those of the visceca of the abdomen and of 

 the lower extremities have this route, yet, from the observa- 

 tions of Mr. Lippi, of Florence, as mentioned, they have also 



