THE THORACIC DUCT. 



941 



in the 

 being- venous 



cords and germ-centres respectively, and the sinus-element, represented by channels 

 resulting from the multiplicatioijfcjf the lymph-vessels. The former, or vascular factor, 

 is constant and present in the Amplest nodule ; the sinus-element, on the contrary, 

 varies, sometimes (as in the usual type of node) being developed from numbers 

 of closely packed lympb-ducts 



and, therefore, of lymphatic Fig. 794. 



origin, and at other times (as 

 hemolymph nodes) 

 channels occu- 

 pied by blood. By the sub- 

 sequent intergrowth of the 

 lymphoid element and the 

 greatly multiplied lymph- 

 capillaries, the intervening 

 bridges of connective tissue 

 are reduced in thickness until 

 finally only the reticulum 

 remains and the lymphoid 

 tissue is ultimately brought 

 into intimate relation with 

 the surrounding sinus. In 

 certain nodes the sinus retains 

 its character as a direct out- 

 growth from the veins and 

 becomes filled with erythro- 

 cytes. Such nodes assume the 

 peculiarities of hemolymph 

 nodes, in which 

 sinuses replace 

 convey lymph, 

 has emphasized, 

 is the anatomical 



the blood 

 those that 

 As Sabin 

 the follicle 

 well 



as 



as 



the vascular unit, the simplest 

 nodule consisting of a single 

 follicle. The latter may be 

 without a sinus, or surrounded 

 by one which is either a lym- 

 phatic or a venous channel. 



Developing lymphatics in rabbit embrj'o of 21 mm. (17 days); X 6. 

 Lymphatic vessels are heavily shaded ; veins are light; for significance 

 of lettering see preceding figure; in addition, O., cephalic ; Br., bra- 

 chial; R., radial; 3'^., subscapular; .Sc/., sciatic ; Fe., femoral; //., 

 iliolumbar. {F. T. Lewis.*) 



In describing the various 

 lymphatic vessels and nodes it 

 will be *convenient to consider 

 first the great terminal trunks 

 of the system, the thoracic 

 and right lymphatic ducts, 

 and then discuss the remaining 

 portions of the system from 

 the topographical standpoint. Attention will be directed primarily to the nodes 

 of each region, the course of the lymph-paths from each organ and their relations 

 to the nodes being subsequently considered. 



THE THORACIC DUCT. 



The thoracic duct (ductus thoracicus) (Fig. 795) extends from the lower border 

 of the second lumbar vertebra, through the entire length of the thorax, to open into 

 the left subclavian vein close to the point where it is joined by the left internal 

 jugular. Its entire length is from 43-46 cm. (17-18 in.). The duct lies at first in 



* Amer. Jour, of Anatomy, vol. v., 1905. 



