330 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



nective tissue, in the mesenteries and the walls of the alimentary 

 canal, and as a network in close relation to the blood-vessels in all 

 parts of the body. 



The lymph hearts are enlarged portions of the lymph-vessels 

 which have contractile walls, are provided with valves to prevent 

 backflow of the fluid and which force the lymph into the veins. Usu- 

 ally they are near the entrance of the lymph-vessels into the veins. 

 In most cases these hearts contract by means of the intrinsic muscles 

 of the walls, but in some urodeles {Amhly stoma, Salamandra, fig. 

 354, A) there is an unpaired lymph heart beneath the truncus arte- 



FiG. 354. Fig. 355. 



Fig. 354. — A, truncus and cardiac lymph heart of Salamandra, after Greil; B, 

 entrance of lymph-vessel into a vein, after Weliky. a, aortic arch; c, carotid; I, left 

 revehent lymph-vessel; containing valves; ly, lymph heart; p, pulmonary arch; r, 

 right revehent lymph-vessel; s, spiral valve of truncus; t, advehent lymph-vessel; t, 

 vein; »/, valve at entrance of lymph into vein; s, fifth aortic arch. In A the heavy dotted 

 line indicates the anterior extent of pericardium. 



Fig. 355. — Scheme of caudal lymph heart of teleost, after Favaro. a, atrium; /, lymph 

 vessels; Is, lymph sinus; v, ventricle; vs, venous sinus of caudal vein. 



riosus in such relations that it enlarges and contracts with the systole 

 and diastole of the blood-vessels. 



As was intimated above there is a constant osmosis of fluid from 

 the blood capillaries into the surrounding tissues. This finally passes 

 into the distal capillaries of the lymph system, while in the walls of 

 the alimentary canal there are, in addition, the results of the digestive 

 processes added to the fluid in the lymph-vessels. As this latter 

 portion has a milky appearance, due to the contained fat, it is called 

 chyle and the lymphatics which contain it are called lacteals and 

 chyle ducts. All of these additions to the contents of the lymph- 



