66 THE VILLI. 



parts of the body, especially in regard to their villi and their 

 follicles. 



Of the Villi, and Papilla. 



On the free surface of the mucous membranes are found a 

 great number of papillary projections springing up from the 

 chorion or dermis of these membranes ; on the small intestines 

 they are so elongated and prominent, as to resemble the pile on 

 a piece of velvet, and have there been called villi. (See fig. 

 141, page 74.) Each villus, minute as it is, is formed of sepa- 

 rate parts arranged in a bundle consisting at least of one artery, 

 vein, nerve and absorbent, woven together by cellular tissue and 

 covered in by a thinly expanded fold of the mucuos membrane. 

 The papillae on the tongue, instead of a mucous layer are cover- 

 ed 'by the epidermis, (periglottis,) which is so thick in many 

 quadrupeds, as to constitute a hard corneous covering, and con- 

 vert the papillae into instruments of prehension. In the pharynx 

 and oesophagus the papillae hold a sort of middle station between 

 those of the tongue and those of the stomach. 

 The papillae of the mucous membrane of the stomach, were 

 formerly described as villi ; and Gendrin proposed for distinction, 

 to call the gastro-intestinal the villous mucous membrane. But 

 this distinction will not hold. At early periods of foetal life, villi 

 are found on the mucous membrane of the stomach, but subse- 

 quently to birth, we discover only flattened papillary projections. 

 The villi properly speaking are now considered as papillae in a 

 modified form belonging only to the small intestines, where they 

 serve the purpose of facilitating the absorption of the chyle. 

 If we examine by the aid of a strong glass, the mucous 

 membrane of the stomach under water exposed to the strong 

 light of the sun, we perceive the whole surface covered by 

 irregular and very superficial nipple-like projections and marked 

 by shallow grooves passing over the surface of the membrane, 

 so as to give it the appearance somewhat of the intestinal con- 

 volutions. These nipple-like projections are covered by fringed 

 or flattened papillae, and between them are seen the honey- 



