ABSORPTION. 39 



raent well adapted for absorption. It is now well known that in the 

 absorption of the products of digestion the blood capillaries are more active 

 than the lymphatic capillaries. 



Lymphatic Vessels. The lymphatic vessels constitute a system of 

 minute, delicate, transparent vessels, found in nearly all the organs and tissues 

 of the body. Having their origin at the periphery in the lymphatic capil- 

 laries and spaces, they gradually converge toward the trunk of the body and 

 empty into the thoracic duct. In their course they pass through numerous 

 small ovoid bodies, the lymphatic glands. 



The lymphatic vessels of the small intestine (M<? lacteah] arise within 

 the villous processes which project from the inner surface of the intestine 

 throughout its entire extent. The wall of the villus is formed by an eleva- 

 tion of the basement membrane, and covered by a layer of columnar epi- 

 thelial cells. The basis of the villus consists of adenoid tissue, fine plexus 

 of blood vessels, unstriped muscular fibres and the lacteal vessel. The 

 adenoid tissue consists of a number of intercommunicating spaces, con- 

 taining leucocytes. The lacteal vessel possesses a thin, but distinct wall, 

 composed of endothelial plates, with here and there openings, which bring 

 the interior of the villus into communication with the spaces of the adenoid 

 tissue. 



The structure of the larger vessels resembles that of the veins, consisting 

 of three coats. 



i. External, composed of fibrous tissue and muscular fibres, arranged 

 longitudinally. 2. Middle, consisting of white fibrous and yellow elastic 

 tissue, non-striated muscular fibres, arranged transversely. 3. Internal, 

 composed of an elastic membrane, lined by endothelial cells. 



Throughout their course are found numerous semilunar valves, looking 

 toward the larger vessels, formed by a folding of the inner coat and 

 strengthened by connective tissue. 



Lymphatic Glands. The lymphatic glands consist of an external 

 capsule composed of fibrous tissue which contains non-striped muscular 

 fibres : from its inner surface septa of fibrous tissue pass inward and sub- 

 divide the gland substance into a series of compartments which communi- 

 cate with each other. The blood vessels which penetrate the gland aru 

 surrounded by fine threads, forming a follicular arrangement, the meshes of 

 which contain numerous lymph corpuscles. Between the follicular threads 

 and the wall of the gland lies a lymph channel traversed by a reticulum of 

 adenoid tissue. The lymphatic vessels after penetrating this capsule pour 

 their lymph into this channel, through which it passes ; it is then collected 



