488 ABDOMEN 



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 individuals they may disappear 

 almost entirely. 



The solitary lymph nodules are isolated lymph follicles, 

 scattered everywhere over 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 plica circulares, the w7A\ 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 by a clear line of demarcation the jejunum 

 from the ileum, 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 would 

 guide him in deciding which is ileum and which jejunum : 



JEJUNUM. ILEUM. 



Plica Circulates. 



Few in number and poorly de- 

 veloped, and, in its lower part, 

 absent altogether. 



Villi. 



Numerous and large. j Not so numerous and not so 



large. 



Aggregated Lymph Nodules. 



Numerous and well marked. 



Few in number, small in size, 

 and, as a rule, nearly circular 

 in outline. 



More numerous, of large size, and 

 oblong in form. 



The general position and the constituent portions of the 

 large intestine have already been noted (p. 439) ; the positions 

 and relations of the individual parts must now be studied 

 more completely. 



The Caecum and Vermiform Process. The caecum forms 

 the commencement of the large gut. It has the appearance 

 of a sacculated pouch, 2\ inches long and 3 inches broad, 

 continuous above with the ascending colon, and on the 



