543 THE THORACIC DUCT. 



at 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 effectually preventing the reflux of either 

 chyle or blood into the duct. 



Varieties. The thoracic duct is not always a single trunk throughout its whole extent ; 

 it is frequently divided for some distance into two vessels which afterwards unite, especially 

 in the lower part of its course (normal according to Teichmann) ; sometimes it separates into 

 three divisions, or even presents a plexiform arrangement, for a short distance. In very rare 

 cases the duct is double throughout, the two canals opening into the right and left innomi- 

 nate veins ; or it is represented by two vessels, which are placed one on each side of the aorta, 

 and unite at the root of the neck into a single trunk (Nuhn, Turner). Cruikshank, in one 

 case, found the duct " 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 common, trunk ; less frequently one of the branches passes 

 across to the veins of the right side of the neck. It is stated by Teichmann that the termina- 

 tion of the thoracic duct, as well as of the right lymphatic duct, is regularly multiple ; the 

 number of terminal branches may be as many as eight on the left side, and five on the right. 

 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. As a rare occurrence the trunk has been found passing 

 upwards through the posterior mediastinum on the left side of the aorta. In cases of per- 

 sistence of the right aortic root, either as a part of a right aortic arch or as a dorsal origin of 

 the right subclavian or vertebral artery, the thoracic duct generally terminates in the veins 

 of the right side : a similar termination has also been observed with a normal arrangement 

 of the great arteries (Morrison Watson). In two instances the thoracic duct has been seen 

 entering the large azygos vein (Wutzer, Arnold). (Teichmann, " Ueber die Ausmiindung der 

 Lymphgefasse in die Venen beim Menschen," Krakauer Akad. d. Wissensch., 1887 ; Arthur 

 Thomson. " Variations of the Thoracic Duct associated with Abnormal Arterial Distribu- 

 tion," Journ. Anat., xvii, 1884 ; J. Szawlowski, " Ueber das Verhalten des Ductus thoracicus 

 bei Persistenz der rechten absteigenden Aortenwurzel," Anatom. Anzeiger. 1888.) 



EIGHT LYMPHATIC DTJCT. 



The right lymphatic duct is a short vessel, about 2 mm. or a little more in 

 diameter, and from a quarter to 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, 

 part of the right side of the chest, the right lung and the right half of the heart, 

 and 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. The vessels which usually unite to form 

 this trunk, however, frequently ^terminate independently in the large veins. 



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 superficial lymphatics of the lower 

 part of the trunk, converge to the superficial inguinal glands, with the exception of 

 a few which dip into the popliteal space. Those of the deep series enter the deep 

 inguinal glands. 



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

 number, surround the popliteal vessels, and are embedded in a quantity of loose fat. 

 They receive from below the deep lymphatics of the leg, and a few superficial ones 

 which accompany the short saphenous vein ; their efferent vessels ascend with the 

 femoral vein to the groin. 



The superficial inguinal glands vary much in number, but are generally 

 between ten and fifteen : they are divisible into a superior or oblique and an 

 inferior or vertical set. The superior glands lie in the line of Poupart's ligament, 



