THE LACTEALS. 



603 



The lacteals, which may be said to be limited to the small intestine, 

 below the entrance of the bile-duct and pancreatic duct, resemble the 

 lymphatics of the stomach, large intestine, and other parts of the body, 

 and, like them, convey, when not engaged in absorbing food, only a 

 transparent lymph. The lacteals were discovered by Aselli (1622) ; 

 their connection with the thoracic duct was shown by Pecquet (1651). 

 In the mucous membrane of the stomach and large intestine, the ab- 

 sorbents probably arise by networks, like those of other membranes. 

 In the small intestine, however, which is the proper seat of lacteal ab- 

 sorption, besides a network near the general mucous surface, absorbent 

 vessels, which form, as it were, the radicles or absorbent extremities 

 of the lacteal system, commence within the villi which specially char- 

 acterize this part of the intestinal canal. These villi, during digestion, 

 project into the pulpy digested food, as the rootlets of a plant, with 

 their absorbing spongioles, depend in water or penetrate the soil. 



The lacteals commence within the villi by closed extremities, and 

 not by open mouths (Fig. 102, 1). By some anatomists they are said 

 to arise by a plexiform network, which, at the base of the villus, passes 

 into larger vessels. According to others, a single lacteal vessel occu- 



Fig. 102. 



Fig. 103. 



Fig. 102. Two intestinal villi highly magnified, showing the two supposed modes of commencement of the 

 lacteals, 1, in their interior; one mode, by a dilated ampulla, the other by a network. The columnar epi- 

 thelial cells. 2, covering the villi, are also shown ; and likewise a portion of the capillary network, 3, lying 

 outside the lacteal vessel. The larger lacteals at the base of the villi are indicated. 



Fig 103. The artery, capillary network, and vein of an intestinal villus artificially injected. The light- 

 colored vessel represents the minute artery which conveys the blood into the villus; the dark vessel is the 

 vein along which the blood returns ; the intermediate capillary network is marked 2. 



pies the centre of each villus, commencing near the apex by a simple 

 closed extremity, by a dilated ampulla, or by a loop, which may be 

 part of a network, and ending in the general network at its base. The 

 diameter of the lacteals in the villi, is from y 



to 5 J th of an inch. 



