THORACIC DUCT. 451 



emanating from and leaving the gland, the vasa efferentia, or 

 efferent vessels. The efferent, fewer but larger than the afferent, 

 after a short course unite to form larger vessels. Sometimes a 

 depression on the surface of a gland, the hilus, marks the spot 

 where the efferent vessels leave it. 



The closed glands of the stomach, intestines, tongue, &c., con- 

 sist of a material resembling that of the lymphatic glands, and 

 which has been termed lymphoid or adenoid tissue; it consists 

 mainly of retiform connective tissue and colourless corpuscles. 



LYMPH AND CHYLE. 



Lymph is a coloiirless fluid, containing a number of objects 

 which resemble almost perfectly the white corpuscles of the blood ; 

 these are the lymph corpuscles, and they are believed to be formed 

 in lymphoid tissue, but notably in the lymphatic glands, and 

 conveyed thence by the efferent vessels. 



Chyle is a milky fluid found in the lacteals or lymphatic 

 vessels of the intestines during digestion ; it contains corpuscles 

 similar to those of the lymph. Since both the lacteal and pos- 

 terior lymphatic vessels lead to the great lymphatic trunk, or 

 thoracic duct, it follows that the lymph and the chyle become 

 mixed. 



THORACIC DUCT. 

 (Fie. 170.) 



This, the largest and longest lymphatic vessel, receives all the 

 others, except those of the right anterior extremity, and right 

 side of the head, neck, and thorax ; it originates in the lumbar 

 region between the posterior aorta and vena cava, by a very 

 irregular dilatation called the receptaculum chyli. or reservoir of 

 Pecquet, into which flow the contents of the neighbouring vessels. 

 From the anterior aspect of this reservoir, the duct proceeds for- 

 wards on the right side of the vertebral column, enters the 

 thoracic cavity through the aortic hiatus of the diaphragm, passing 

 along the vertebrae until it reaches about the sixth dorsal, where 

 it curves downwards to the left side, over the base of the heart, 

 and towards the beginning of the anterior vena cava, in most cases 

 terminating in the jugular confluent, about the anterior border 

 of the first rib. Its orifice is dilated and guarded by a valve, 

 which prevents the influx of blood ; it may be double, when we 



