CHAPTER XXII. 



THE LYMPHATIC SYSTEM AND THE DUCT- 

 LESS GLANDS. 



The Lymphatics or Absorbents form close networks in 

 nearly all parts of the Body. Most organs, as has been 

 pointed out (p. 62), possess a sort of internal skeleton made 

 up of connective tissue, which consists mainly of bundles of 

 fibres, united together and covered in by a "cement" sub- 

 stance. In this substance are found numerous cavities, 

 usually branched, and communicating with one another by 

 their branches. They frequently contain connective-tissue 

 corpuscles, which, however, do not completely fill them; 

 and they thus, with their branches, form a set of intercom- 

 municating channels known as the "serous canaliculi;" 

 these are filled with lymph and constitute the origin of 

 lymphatic vessels in many organs. Elsewhere the com- 

 mencing lymphatics seem to be merely interstices (lacuna) 

 between the constituent tissues of an organ; this is espe- 

 cially the case in glands. Such spaces differ from the se- 

 rous canaliculi in being lined by a definite epithelium. 



Structure of Lymph- Vessels. The serous canaliculi and 

 lymph-spaces open into better defined channels, lined with 

 a single layer of wavy-edged flattened epithelial cells. 

 These form networks in most parts of the Body and are 

 known as the lymph capillaries. They are usually wider 

 than blood capillaries. From the capillary networks 

 larger vessels arise which in structure resemble veins, and 

 have similar, but more numerous, valves. 



The Thoracic Duct. All the lymphatics end finally in 

 two main trunks which open into the venous system on each 

 side of the neck, at the point of junction of the jugrlai- and 



