342 



COMPARATIVE PHYSIOLOGY. 



(Peyer's patches) and thickly studded with villi, giving the 

 small gut that velvety appearance appreciable even by the 

 naked eye. 



It will not be forgotten that the capillaries of the digestive 

 organs terminate in the veins of the portal system, and that the 

 blood from these parts is conducted through the liver before it 

 reaches the general circulation. '• 



Main venous trunk 



Bight aurkle 



Vena cava 



Hepatic Vein- 



Portal system 



Alimentary tract 



Fig. 277.— Diagram intended to illustrate the general relations ot blood and lymph to 

 metabolism (nutrition), and the method by which the portal, lymphatic, and gen- 

 eral venous systems are related to the alimentary tract. 



The lymphatics of these organs form a part of the general 

 lymphatic system of the body ; but the peculiar way in which 

 absorption is effected by villi, and the fact that the lymphatics 

 of the intestine, etc., at one time (fasting) contain ordinary 

 lymph and at another (after meals) the products of digestion, 

 imparts to them a physiological character of their own. 



Absorption will be the better understood if we treat now of 

 lymph and chyle and the lymph vascular, system, which were 

 purposely postponed till the present; though its connection 

 with the vascular system is as close and important as with the 

 digestive organs. 



The lymphatic system, as a whole, more closely resembles 

 the venous than the arterial vessels. We may speak of lym- 

 phatic capillaries, which are, in essential points of structure, 

 like the arterial capillaries; while the larger vessels may be 

 compared to veins, though thinner, being provided with valves 

 and having very numerous anastomoses. These lymphatic 



