484 LABORATORY MANUAL OF HUMAN ANATOMY 



(d) Mucous coat (tunica mucosa). This will be studied in continuity. 

 Can you make out the lamina muscularis mucosae? 



Open the remainder of the small intestine along its mesen- 

 teric border, using an enterotome, and proceed to the study of 

 the 



(a) Circular folds (plicae circulares [Kerkringi]) (0. T. valvulae con- 

 niventes). (Fig. 254.) What happens to these folds when the in- 

 testinal wall is put upon the stretch 1 ? How far above the ileocaecal 

 valve (valvula coli) do they disappear? These folds are occasion- 

 ally found extending as far as the ileocaecal junction in diseases 

 such as tuberculosis of the peritoneum, where the total length of 

 the small intestine is shortened. Cruveilhier and Kazzander have 



FIG. 254. 



Tunica serosa -m 



-^^^n 



Plicae circulares [Kerkringi] 



Tunica mucosa v ^ ^ - 5 S1 '' 



\ 



A piece of the intestinum jejunum in part cut open. (After Toldt, Anat. Atlas, Wien, 1900, 



2 Aufl., p. 426, Fig. 698.) 



seen them extending thus far in cadavers in which no disease of the 

 peritoneum or intestine could be detected. Three forms are to 

 be found, according to Kazzander. Most of the folds extend only 

 part way about the wall of the gut; others surround the wall com- 

 pletely; while the third set has a spiral arrangement. Can you 

 find one of each variety? They number 678 in the male and 644 

 in the female (Kazzander). What coats of the intestine enter into 

 the formation of these folds'? What effect does this arrange- 

 ment have? How do you explain their formation? Folds which 

 are parallel to the long axis of the bowel are occasionally found. 

 Upon what factors does their formation depend? Do you find any 

 in your subject? 

 (6) Intestinal villi (villi intestinales) . Wash the mucous membrane clean 



