THE IXTESTIXAL CAXAL. 



1023 



over the valvuhe conniventes as well as between them (Fig. 639). They give to 

 the surface its velvety appearance. Between the bases of the viili, wherever they 

 are. the mouths of the glands of Lieberkiihn are seen (Figs. 640 and 642). They 

 are lar-ot and most numerous in the duodenum and jejunum, resembling the 

 valvulaT conniventes in distribution. They are smaller and fewer in the ileum. 

 and stop abruptly at the ileo-c*cal orifice. There are none in the large intestine. 

 Thev measure .5* to .7 mm. in length, and are present to the number of about 

 four* millions (Krause) ; 10 to 18 per sq. mm. in the upper intestine, and 8 to 14 

 to the same space in the ileum. They are apt to be leaf-shaped in the duode- 

 num, tongue-shaped in the jejunum, and filiform in the ileum. 



Structure of the Villi (Fig. 641). The structure of the villi has been studied 

 recentlv bv many eminent anatomists. We shall here follow the description of 

 Dr. Watney, 1 whose researches have a most important bearing on the physiology 



Capillaries. 1ft r | g>~ 4 



J ^ 



Lymph trunk.'-K^^^ 



\ "' " 



-1* ^ - t =--%=-! 5 = ' 



Ma 's;l ss|ii\ 



^ I I^Vml 



^^1 lAf'lift: 



-I-" 



" ~ Capillaries. 



Small artery.' LtfmpJtatic plexus. 



FIG. fri2. Villi of small intestine. (Cadiat.) 



of that which is the peculiar function of this part of the intestine, the absorp- 

 tion of fat. 



The essential parts of a villus are the lacteal vessel, the blood-vessels, the 

 epithelium, the basement membrane and muscular tissue of the mucosa, these 

 structures being supported and held together by retiform lymphoid tissue. 



These structures are arranged in the following manner : situated in the centre 

 of the villus is the lacteal, terminating near the summit in a blind extremity ; 

 running along this vessel are unstriped muscular fibres : surrounding it is a plexus 

 of capillary vessels, the whole being enclosed by a basement membrane, supporting 

 columnar epithelium. Those structures which are contained within the basement 

 membrane namely, the lacteal, the muscular tissue, and the blood-vessels are 

 surrounded and enclosed by a delicate reticulum which forms tbe matrix of the 

 villus. and in the meshes of which are found large flattened cells, with an oval 

 nucleus, and. in smaller numbers, lymph-corpuscles. These latter are to be 

 distinguished from the larger cells of the villus by their behavior with reagents, by 

 their size, and by the shape of their nucleus, which is spherical. Transitional 

 forms, however, of all kinds are met with between the lymph-corpuscle and the 

 proper cells of the villus. 



The lacteals are in some cases double, and in some animals multiple. Situated 



1 Phil. Trans., vol. clxvi. pt. ii. 



