68 VESSELS AND NERVES OF MUCOUS MEMBRANES. 



a higher estimate of their number than this. They assert 

 that there are 4000 to be seen upon every square inch of surface, 

 and which by their calculation would make a million of villi to 

 the small intestines. 



Those of the jejunum, according to the measurements of 

 Dr. Homer, are the thirtieth of an inch in length, and those of 

 the ileum the sixtieth. In the pyloric half of the stomach and 

 in the duodeum, according to Beclard, they are formed of a 

 fold of the mucous membrane, tufted on its margins, the trans- 

 verse diameter of which exceeds the length. In the jejunum 

 they consist of longer folds, forming semi-oval plates touching 

 one another at their basis. In the ileum, according to Dr. Hor- 

 ner, they form slightly conical projections. 



The villi can be studied to the best advantage after a minute 

 injection of the vessels of the mucous membranes, which by 

 rendering those of the villi turgid, throws them into a state of 

 erection, like that which takes place in the papillae of the skin 

 when they are in a state of functional activity. The villi of 

 the small intestines which will be subsequently considered,* are 

 peculiarly organized in some respects, apparently for the purpose 

 of fitting them for a function which they alone possess that of 

 chylous absorption. 



The Vessels and Nerves of Mucous Membranes. 



In the submucous cellular or nervous tissue, are found the 

 larger branches of the arteries, veins, and nerves, which ramify 

 finally in the mucous membranes and their villous or papillary 

 prominences. The vessels are derived from contiguous trunks 

 The veins are far more numerous than the arteres, and seem 

 to exceed here the large proportion which the bear to the 

 arteries in other portions of the body. They form, as shown 

 by the elegant preparations of Professor Horner, a plexus 

 on the surface of the membrane, which overlays the arte- 

 ries, and in which, when successfully injected, a straggling 

 arterial branch is only here and there visible. Beneath this 



* See General Anatomy of Absorbent System. p. 



