Anatomy, physiology and hygiene . Fig. 52. Section of Small Intestine, showing Valvulae Con-niventes (Testttt). Wide perpendicular line =muscle ; line on left = fibrous coat ; line on right= mucous membrane. They retarda lonerer time 1 A membrane which secretes a thin whey-like thud called serum. Asimilar membrane, under the name o( the peritoneum^ incloses, for themost part, all the abdominal viscera, in the same way. 120 DIGESTION. to the action of the digestive fluids. They also providea very large surface for secretion and absorption. The characteristic velvety condition of the mucousmembr
Anatomy, physiology and hygiene . Fig. 52. Section of Small Intestine, showing Valvulae Con-niventes (Testttt). Wide perpendicular line =muscle ; line on left = fibrous coat ; line on right= mucous membrane. They retarda lonerer time 1 A membrane which secretes a thin whey-like thud called serum. Asimilar membrane, under the name o( the peritoneum^ incloses, for themost part, all the abdominal viscera, in the same way. 120 DIGESTION. to the action of the digestive fluids. They also providea very large surface for secretion and absorption. The characteristic velvety condition of the mucousmembrane is due to its millions of minute elevations, pre-senting a general appearance of plush, and known asintestinal villi. Through them the process of absorption is. Fig. 53. Villi of Small Intestine, with their superficial arteries and veins distended.(Magnified 100 diameters.) mainly effected. Each villus is composed of a frameworkof connective tissue, upon the free surface of which isthe epithelium, — a single layer of cells. In the centre ofthe framework is a small vessel, with a closed end near theupper extremity of the villus. This is called a lacteal,1 andis an offshoot of a system of absorbent vessels distributedthroughout the body, named lymphatics. 1 So called because during digestion it is filled with a milk-white fluid,consisting mainly of fat, which it has taken up from the intestine. Duringthe intervals of digestion these vessels are not readily seen. Sometimesthe lacteals are double. DIGESTION. 121 The lacteals empty into the receptaculum cliyli ( re-ceptacle of the chyle), a pouch lying upon the lumbarvertebrae. This pouch connects with the thoracic duct, asmall tube which extends upwardsand empties into the left subclavianve
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