Chap, iv.] ENTERON OF VERTEBRATES. 



169 



the number of which varies considerably in different 

 forms, have been sometimes found to be full of food 

 (Spatularia Wieders- 

 heim), and are cer- 

 tainly developed in 

 inverse proportion to 

 the spiral valve itself. 

 They are only one of 

 the many means by 

 which vertebrate ani- 

 mals increase the ab- 

 sorbing surface of their 

 intestine without en- 

 croaching greatly on 

 the space occupied by 

 the other organs of the 

 abdominal cavity. 



In some Amphibia, 

 as in Siren, the differ- 

 ence in calibre be- 

 tween the small and 

 large intestine is not 

 very well marked ; in 

 others, as the frog, 

 there is a considerable 

 difference. The same 

 kind of difference is 

 seen among the Rep- 

 tilia ; for the Ophidia 

 and the Amphisbcena 

 have the greater part 

 of the tract of the same 

 width, and the whole intestine is less coiled than in forms 

 with a shorter body, such as the Chelonia or the Croco- 

 dilia. In Birds the first duodenal loop of the intestine 

 always encloses the pancreas ; the intestine is propor- 

 tionately long, but while nesting-birds, such as the 



Fig. 77. Diagram of the General Ar- 

 rangement of the Abdominal Portion 

 of the Intestine of Mammalia, seen 

 from in front ; the small intestine is 

 greatly abbreviated. (After Flower.) 



p, Pylorus ; d, duodenum ; i, ileum ; 

 r, rectum. 



