ABDOMINAL CAVITY 329 



each corresponds in its direction with that of the intestine 

 itself. 



In the lower part of the ileum the aggregated nodules 

 may be from 25 mm. to 100 mm. (i to 4 inches) long, and 

 12.5 mm. (half an inch) broad, but higher in the ileum 

 they become much smaller and not nearly so numerous, and 

 they are either few in number, or entirely absent, in the 

 jejunum. The total number varies much, but the average 

 number may be stated to be about thirty. They are more 

 numerous in the young, and not so abundant nor so distinctly 

 marked out in later periods of life. Indeed, in very old 

 subjects they may disappear almost entirely. 



The solitary lymph nodules are isolated lymph follicles, 

 scattered everywhere in the mucous membrane of the small 

 intestine. They are minute, rounded or ovoid, opaque 

 white bodies, about the size of a millet seed, and they 

 usually cause a slight bulging of the mucous membrane at 

 the points where they occur. 



The plicce. circulares, the villi, and aggregated lymph nodules 

 are the only special peculiarities of the mucous membrane of 

 the jejunum and ileum which are visible to the naked eye ; and, 

 from what has been said regarding them, the dissector will 

 understand that, although they are not arranged in such a 

 way as to mark off the jejunum from the ileum by a clear line 

 of demarcation, they are sufficient to enable him to distinguish 

 between characteristic portions of each i.e. between portions 

 taken at some distance from the arbitrary line of division. The 

 following are the essential points of difference which should 

 guide him in deciding which is ileum and which jejunum : 



JEJUNUM. ILEUM. 



Plica Circulares. 



Few in number and poorly de- 

 veloped, and, in its lower part, 

 absent altogether. 



Villi. 



Not so numerous and not so 



Numerous and well marked. 



Numerous and large. 



large. 

 Aggregated Lymph Nodiiles. 



Few in number, small in size, 

 and, as a rule, nearly circular 



More numerous, of large size, and 

 oblong in form. 



in outline. 

 The general position and the constituent portions of the 



