ABSORPTION 



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contractions in the neighbourhood of the vessels, by which means 

 they are compressed and their contents forced onwards, since 

 the valves which the vessels contain prevent a back flow. The 

 obstruction caused by the lymphatics passing through glands is 

 not serious, while the involuntary muscle fibres in the capsule of 

 the gland more than compensate by their contraction for any 

 resistance in the gland itself. The pressure of the lymph in the 

 lymph- vessel is higher than that in the jugular vein, so the flow 

 of lymph from the tissues to the vein is assisted by the fact that 

 the fluid is passing from a region of higher to one of lower pres- 

 sure. The movements of the diaphragm, tendons, and fasciae 

 produce an aspirating effect on the lymph circulating through 

 them. In the case of the diaphragm the lymphatic vessels drain 

 the two large lymphatic sacs, the pleura and peritoneum ; 

 owing to the direction taken by the fibres of the diaphragm, 

 compression is exerted on the lymph spaces during its contraction, 

 while a sucking action is produced when it relaxes. This pumping 

 arrangement exists in tendons, fasciae of muscles, etc., and is a 

 valuable aid in lymph circulation. In the ordinary skeletal 

 muscles during contraction the lymph'is squeezed out of the part 

 by compression. During rest practically no lymph passes by the 

 lymph-vessels of muscle, the exchange taking place, as we have 

 seen, by the bloodvessels. 



Once the lymph from the abdominal viscera and hind-quarters 

 has found its way into the thoracic duct, its passage into the 

 general circulation is favoured by gravity, by the muscular con- 

 traction of the coats of the duct, and by movements of the skeletal 

 muscles, especially the abdominal. The lymph from the right 

 side of the face, neck, and right thorax has a duct of its own, 

 and this is so situated that gravity plays an important part in 

 moving its contents along. Both the thoracic duct and the right 

 lymphatic duct empty into the veins near the heart, either the 

 anterior vena cava or the jugular confluent. The mode of entry 

 varies ; in fact, there are great variations in animals of the same 

 species, in the anatomical arrangements, not only of the ducts, 

 but also of their terminations ; for example, the thoracic duct is 

 frequently duplicated in the ox. 



In whatever way connection with the venous system is made, 

 a valvular arrangement, looking towards the vein, exists between 

 the dilated termination of the lymph-duct and the bloodvessels 

 intended to prevent a reflux of blood into the duct. This valvular 

 seal is a reliable one in the ruminant ; in the carnivora it is less 

 so ; in the horse it is imperfect, so much so that blood may find 

 its way even for some distance into the duct, and stain the con- 

 tents, as first pointed out by Colin. If a manometer tube be 

 placed in the thoracic duct of the ox at its termination in the 



