212 INTESTINAL DIGESTION 



IV, Fig. 6). They adhere together firmly and are isolated with difficulty. 

 The borders of their free ends are thickened and finely striated, this 

 portion forming a thin membrane or cuticle covering the villi. These 

 cells are called cuticularized cells. Between the cylindrical cells, in vari- 

 able number, are the so-called goblet-cells. These probably are modi- 

 fied cylindrical cells, the change in form being due to a secretion of 

 mucin near their free extremities which become swollen, this giving to 

 the cells their peculiar appearance. The mucus finally is discharged, 

 leaving a goblet-shaped cavity, the nucleus and granular protoplasm 

 remaining below. Some histologists regard these as a distinct kind of 

 cells (see Plate IV, Fig. 5). 



The substance of the villi is composed of amorphous matter in which 

 are embedded nuclei, a few fine fibres, connective-tissue cells, lymphoid 

 cells and non-striated muscular fibres. The bloodvessels are very abun- 

 dant ; four or five, and sometimes as many as twelve or fifteen arterioles 

 entering at the base, ramifying through the substance of the villus, but 

 not branching or anastomosing or even diminishing in calibre until, by 

 a slightly wavy turn or loop, they communicate with the venous radicles, 

 which are somewhat larger than the arterioles. The veins all converge 

 to two or three branches, finally emptying into a large trunk situated 

 nearly in the long axis of the villus (see Plate V, Fig. i). 



The muscular fibres of the villi are longitudinal, forming a thin layer 

 surrounding the villus, about halfway between the periphery and the 

 centre and continuous with the muscular coat of the intestine. 



In the central portion of each villus is a small lacteal, one of the 

 vessels of origin of the lacteal system, with an extremely delicate wall 

 composed of endothelial cells with frequent stomata between their bor- 

 ders. This vessel probably is in the form of a single tube, either simple 

 or presenting a few short rounded diverticula. 



The stomata of the lacteal vessels are thought to communicate with 

 lymph-spaces or canals in the substance of the villus. Owing to the 

 tenuity of the walls of the lacteals in the villi, it has been found impossi- 

 ble to fill these vessels with an artificial injection, although the lymphat- 

 ics subjacent to them may easily be distended and studied in this way. 



No satisfactory account has been given of nerves in the intestinal 

 villi. If any exist in these structures, they probably are derived from 

 the sympathetic system. 



The solitary glands, or follicles (lymph-nodes), and the patches of 

 Peyer, or agminated glands, have one and the same structure, the only 

 difference being that those called solitary are scattered singly in very 

 variable numbers throughout the small and large intestine, while the 

 agminated glands consist of these follicles collected into patches of dif- 



