The Intestines. 191 



Its first portion, the blind intestine or caecum (intestinum 

 caecum), distinguished by its great size, is connected with the 

 large intestine proper only in the region of the sacculus rotundus. 

 The organ (Fig. 43) consists of three limbs, and terminates in the 

 narrow but thick-walled, vermiform process (processus vermi- 

 formis) or appendix. The latter lies in a dorsal position, and is 

 directed backward. 



The second portion, the colon, comprising the major portion 

 of the large intestine proper, leaves the caecum in the region of the 

 sacculus rotundus, in which position it is distinguished by its greatly 

 sacculated walls. 



The third portion, the straight intestine, or rectum (intes- 

 tinum rectum) is a small terminal division situated in the middle 

 line and enclosed for the most part by the pelvis. It is scarcely 

 distinguishable from the related portion of the colon. 



5. In the caecum the following features may be distinguished: 



(a) The wall, which is otherwise smooth, is divided by a spirally 

 arranged constriction, the latter denoting the position, 

 internally, of a fold of the mucous tunic, the spiral valve. 



(b) The vermiform process is a narrow, light-colored tube of 

 about five inches in length, the wall patterned, externally 

 by lymph follicles, in the same way as that of the sacculus 

 rotundus, and greatly thickened in comparison with that of 

 the caecum proper. 



6. The colon is divisible into ascending, transverse, and de- 

 scending portions, the relations of which may be traced as follows: 



(a) The ascending colon (colon ascendens) passes from its 

 origin on the caecum to a point forwards on the right side of 

 the dorsal body-wall. This portion is greatly elongated in 

 the rabbit, and instead of passing directly forward (i.e., 

 in man, upward (see Fig. 40), follows more or less closely 

 the course of the caecum. It is composed of five principal 

 limbs, united by flexures. Three of the limbs are directed 

 for the most part forward, the remaining two backward. 



The first limb of the colon bears three rows of small saccu- 

 lations, the haustra, separated by three longitudinal 

 muscle stripes, distinguished as the bands of the colon 



