430 ELEMENTARY ANATOMY. [LESS. 



It has become, as it were, pulled out by the gradual dis- 

 placement downwards of the heart and its arches from what 

 was their primitive position. Its two ends in the meantime 

 retaining their primitive connexions, the whole nerve becomes 

 sharply bent, or " recurrent." 



12. The supplementary part of the circulating organs 

 which goes by the name of the LYMPHATIC SYSTEM has 

 been already described in the second chapter of Professor 

 Huxley's work so often referred to, the " Elementary Physio- 

 logy," ' 5 and 6. 



It will be well, however, here to recapitulate certain lead- 

 ing facts. 



The lymphatic system consists of two sets of vessels (dis- 

 tinguished by their place of origin) termed lacteals and 

 lymphatics. Both are connected with certain rounded 

 structures termed LYMPHATIC GLANDS. 



Each gland consists essentially of a network of finely 

 divided lymphatic vessels, on and amongst which capillary 

 blood-vessels ramify, the whole being compacted together and 

 surrounded by fibrous tissue. 



The central part of the lymphatic system consists of a 

 vertical canal, which ascends in front of the vertebral column 

 and is called the thoracic duct. At its lower end (at the 

 junction of the lumbar and dorsal regions) it is dilated into 

 what is called the receptaculum chyli. 



Into this duct all the lymphatics and lacteals ultimately 

 empty themselves, except those of the right arm and right 

 side of the head, which empty themselves into a small 

 vessel called the right lymphatic duct. 



Both these ducts open into the corresponding innominate 

 veins. 



Lymphatic vessels are provided with valves like man's 

 veins, and exist in all parts of the body ; but in the brain 

 they take the form of investing sheaths for the blood-vessels, 

 which run enclosed in lymphatics as a gas-pipe might run 

 inside a drain-pipe. 



The lymphatic vessels have proper walls, but they originate 

 in mere channels, left, as it were, between the other tissues, 

 and thus whatever is cast loose must find its way into the 

 lymphatics. 



The lacteals are the lymphatics of the alimentary canal, 

 and pass through numerous lymphatic glands which are 

 placed in the membranes (mesenteries) which attach that 

 canal to the spine. 



