YILLI OF THE MUCOUS MEMBRANE. 



843 



Their length varies from |th to ird of a line, or even more ; and the 

 broad flattened kinds are about ^-th or Jth of a line wide, and ^\jth or -^th 

 of a line thick. They are largest and most numerous in the duodenum'and 

 jejunum, and become gradually shorter, smaller, and fewer in number in the 

 ileum. In the upper part of the small intestine Krause has estimated their 

 number at from 50 to 90 in a square line; and in the lower part at from 40 

 to 70 in the same space : he calculates their total number to be at least four 

 millions. 



The structure of the villi is complicated : each consists of a prolongation 

 of the proper mucous layer, covered by epithelium and enclosing blood-ves- 



Fig. 587. MAG- 

 NIFIED VIEW OP 

 THE BLOOD-VES- 

 SELS OP THE IN- 

 TESTINAL VILLI. 



The drawing was 

 taken from a pre- 

 paration injected by 

 Lieberkiihn, and 

 shows in each villus 

 a small artery and 

 vein with the in- 

 termediate capil- 

 lary network. 



Fig. 



sels, one or more lacteal vessels, and fine muscular fibres, with a greater or 

 less number of small granular corpuscles and fat-globules, of various sizes. 



Fig. 588. INJECTED LACTEAL 

 VESSELS IN THE VILLI OP THE 

 HUMAN INTESTINE. 



A, two villi in which the lacteals 

 are represented as filled with white 

 substance and the blood-vessels 

 with dark (from Teichinann) ^ : 

 a, 6, the lacteal vessels, single in 

 one villus and double with cross 

 loops in the other ; e, the hori- 

 zontal lacteal vessels with which 

 those of the villi communicate ; 

 d, the blood-vessels, consisting of 

 small arteries and veins with 

 capillary network between. 



B, injected lacteal (shaded dark) 

 in a villus, showing an example 

 not very common of a looped net- 

 work a, which is connected by a 

 single vessel with the horizontal 

 lacteal vessel 6 : the preparation 

 was made from the intestine of 

 a young man who died suddenly 

 while digestion was going on (from 

 W. Krause). ^ 



Fig. 588. 



A. 



Nerves have not yet been demonstrated in the villi, though they are probably 

 not wanting. Each villus receives one or more small arteiial twigs, which 



