STRUCTURE OF A VILLUS. 



389 



or more lacteals, closely invested with a few longitudinal smooth muscular fibres, 

 derived from the muscularis mucosae, and a plexus of blood-vessels. 



The adenoid tissue of the villus consists of a reticulum of fibrils with endothelial 

 plates at its nodes. The spaces of the adenoid tissue form a spongy net-work of 

 inter-communicating channels containing stroma-cells or leucocytes (Fig. 150, A, e, e). 

 These leucocytes or lymph-corpuscles have been seen to contain fatty granules, 

 and they may, perhaps, play an important part in the absorption of fatty particles. 



The lymphatic or lacteal lies in the axis of the villus (Fig. 149, d). By some 

 observers, the lacteal is regarded merely as a space in the centre of the villus, 

 but more probably it has a distinct wall composed of endothelial cells, with 

 apertures or stomata here and there between the cell-plates. These stomata 

 place the interior of the lacteal in direct communication with the spaces of the 

 adenoid tissue. It is very probable that white blood-corpuscles wander out 

 of the blood-vessels of the villi into the spaces of the adenoid tissue, where 

 they become loaded with fatty granules, and pass into the central lacteal. 

 Zuwarykin and Wiedersheim suppose that the leucocytes pass from the par- 

 enchyma of the villus towards the epithelial layer, and even between the 

 epithelial cells, from which they return towards the axis of the villus, laden 

 with substances which they have taken into their interior (p. 399). 



A small artery placed eccentrically passes into each villus. In man it begins to 

 divide about the middle of the villus, but in animals it usually runs to the apex 

 before it divides. The capillaries resulting from the division of the artery form a 

 fine dense net-work placed superficially, immediately under the epithelium of the 

 surface. The blood is carried out of a villus by one or two veins (Fig. 149, a, c). 



'...at' 



Fig. 151. 



Section of the mucous membrane of the small intestine, showing Lieberkiihn's 

 glands a, with irregular epithelium; b, villi, cut short; c, muscularis mucosse; 

 d t sub-mucous tissue. 



