The Digestion of Food 1 2 5 



The lymphatic vessels gradually unite to form larger 

 vessels and at last join the thoracic duct, except the lym- 

 phatics on the right side of the head and neck, on the 

 right arm and the right lung. These open by the right 

 lymphatic duct into the venous system on the right side 

 of the neck. 



The whole lymphatic system may be regarded as a neces- 

 sary appendage to the blood-vascular system (Chapter VII). 

 It is convenient, however, to treat it under the general topic 

 of absorption, in order to complete the history of food 

 digestion. 



/ 190. The Spleen and Other Ductless Glands. With the 

 lymphatics may be classified, for convenience, a number of 

 organs called ductless glands, because they have no ducts 

 or canals along which may be carried the result of their 

 work. 



The spleen is the largest of these glands. It lies beneath 

 the diaphragm and upon the left side of the stomach. It is 

 of a deep-red color and full of blood. 



The functions of the spleen are as yet but little under- 

 stood. It appears to take some part in the formation of blood 

 corpuscles. In certain diseases, like malarial fever, it may 

 become remarkably enlarged. 



The spleen may be removed from man and from animals 

 without any apparent effect. 



The thyroid is a ductless gland situated beneath the muscles 

 of the neck on the sides of "Adam's apple" and below it. 

 It undergoes great enlargement in the disease called goitre. 



The thymus is also a ductless gland. It is situated around 

 the windpipe, behind the upper part of the breastbone. Until 

 about the end of the second year it increases in size, and then 

 it begins gradually to shrivel away. . Its use is not certainly 

 known. 



The suprarenal capsules are two little bodies, one perched 

 on the upper edge of each kidney, in shape not unlike that 

 of a conical hat. Their functions are important, but as yet 

 nothing definite is known about them. 



