50C THE ABSOEBENT VESSELS. 



describe a curve over the apex of the pleura, and then terminates on 

 the outer side of the internal juo;ular vein, in the angle formed by the 

 union of that vein with the subclavian. The diminution in the size 

 of the duct as it ascends is such that at the fifth dorsal vertebra it 

 is often only two lines in diameter, but above this point it again 

 enlarges. The duct is generally waving and tortuous in its course, 

 and is constricted at intervals so as to give it a varicose appearance. 



The thoracic duct has numerous double valves at short intervals 

 throughout its whole course, the constrictions of their attachments 

 giving a nodulated appearance to the vessel. They are more numerous 

 in the upper part of the duct. At the termination of the duct in 

 the veins there is a valve of two segments, so placed as to allow 

 the contents of the duct freely to pass into the veins, but which 

 effectually prevents the reflux of either chyle or blood into the 

 duct. 



Varieties. — The thoracic duct is not always a single trnnk throughout its 

 whole extent ; it frequently divides oi">posite the seventh or eighth dorsal ver- 

 tebra into two trunks, which soon join again : sometimes it separates for a short 

 distance into three divisions, which afterwards unite, and enclose between them 

 spaces or islets. Crurkshank in one case fomid the duct double in its entire 

 length ; " in another triple, or nearly so."' In the neck, the thoracic duct often 

 divides into two or three branches, which in some instances terminate separately 

 in the great veins, but in other cases unite first into a coiiimon trunk. In a case 

 of right aortic arch the thoracic duct has been observed to end in the veins of 

 the right side (A. Thomson). Dr. Morrison Watson describes a case in which 

 without transposition of the viscera, or any change in the disposition of the 

 branches of the aorta, the thoracic duct terminated in the veins of the right side. 

 and no trace of a left lymphatic duct could be discovered. (" Journ. of Anat.," 

 vol. vi., p. 427.) In the lower animals, the termination of the thoracic duct in 

 the veins of the right side as well as of the left is not uncommon. 



THE EIGHT LYMPHATIC DUCT. 



The right lymphatic duct is a short vessel, about a line or a little 

 more in diameter, and about a quarter or half an inch in length, which 

 receives the lymph from the absorbents of the right upper limb, the 

 right side of the head and neck, the right side of the chest, the right 

 lung, and the right half of the heart, and from part of the upper surface 

 of the liver. It enters obliquely into the receding angle formed by the 

 union of the right subclavian and internal jugular veins, where its 

 orifice is guarded by a double valve. 



LYMPHATICS OF THE LOWER LIMB. 



The lymphatics of the lower limb are arranged in a superficial and a 

 deep series. Those of the superficial series, together with the super- 

 ficial lymphatics of the lower half of the trunk, converge to the super- 

 ficial inguinal glands ; with the exception of a few which dip into 

 the popliteal space. Those of the deep series converge to the deep 

 inguinal ghnuls. 



The popliteal lymphatic glands, usually very small, and four or 

 five in number, surround the popliteal vessels, and are imbedded in a 

 quantity of loose fat. They receive from below the deep lymphatics of 

 tiie leg, and those which accompany the short saphenous vein ; and 



