604: SPECIAL PHYSIOLOGY. 



The network at their hase consists of a finer and a coarser layer, in 

 the latter of which the vessels possess valves. (Teichmann.) The villi 

 are also very vascular, each containing a minute arterial and venous 

 twig, with a close capillary network outside the lacteal vessels (Fig. 

 102, 3, and Fig. 103). The substance of the villus consists of a deli- 

 cate extension of the mucous membrane, composed of a mixed, soft 

 areolar and granular tissue, containing fatty particles ; further, each 

 villus contains, around the central lacteal, a few unstriped muscular 

 fibres, by the contraction of which the villus may be shortened, and 

 its substance thrown into transverse folds; lastly, the epithelial cover- 

 ing of the villus, which measures only about y^^th of an inch in thick- 

 ness, is composed, like that of the intestine generally, of a single layer 

 of columnar nucleated cells, pointed at their attached end, but wider, 

 flattened, and more or less polygonal at their free extremity. This 

 part of the cell has been described as being ciliated, but the appear- 

 ance is generally attributed to the existence of fine lines passing from 

 the free end to the interior of each cell, and regarded by some as pores. 

 In animals killed while lacteal absorption is going on, these epithelial 

 cells are frequently found to be distended with fatty matter, the villi 

 having a swollen and tuberculated aspect. At this time also, the cen- 

 tral lacteals of each villus, and also the subjacent vessels, are found 

 distended with whitish or bluish chyle. Upon the surface of the small 

 intestine (Fig. 104, 1), running beneath the peritoneal coat towards 

 its attached border, are seen larger chyliferous vessels, proceeding 

 between the layers of the mesentery, 2, 2; thence others, passing 

 through the mesenteric glands, 3, converge to the back of the abdomen, 

 where they end in the receptaculum chyli, or dilated part of the tho- 

 racic duct (Fig. 100, a). If this duct be tied immediately after death, 

 in an animal killed during digestion, it, as well as the chyliferous ves- 

 sels generally, becomes much distended, and either of these vessels 

 may burst, and the chyle may be extravasated at many points. 



Beneath the mucous membrane in various parts of the alimentary 

 canal, as in certain recesses at the root of the tongue (p. 520), and in 

 the tonsils (p. 501), or scattered singly over the internal surface of the 

 stomach, small intestine, and large intestine, and, lastly, collected in 

 patches in the small intestine, there exist peculiar saccular bodies, 

 called glands, which, however, do not appear to belong to the secreting 

 gland system, but perhaps rather to the absorbent system. They are 

 neither racemose glands, like the glands of Brunner, nor open follicles, 

 nor tubuli, like the gastric glands and the crypts of Lieberkuhn, but 

 closed sacs, not communicating with the interior of the intestine, un- 

 less under some exceptional conditions. In the stomach and intestine, 

 these bodies exist in two forms. First, as the so-called solitary glands 

 of the stomach (p. 526), small intestine (p. 544), and large intestine 

 (p. 544), scattered over the mucous surface, as small soft' whitish bodies, 

 somewhat prominent, and about one line in diameter, or the size of a 

 millet-seed when they are fully distended. Each sac consists of a 

 thickish soft capsule, composed of an indistinctly formed areolar tissue, 

 mixed with nuclei, and incloses a semi-opaque, adherent, and semi- 



