DIGESTIVE SYSTEM. 335 



inch in diameter, which occur at intervals along 

 the whole length of the small intestine, on the 

 side opposite to the attachment of the mesentery. 



b. The sacculus rotundus is the dilated distal end of 

 the small intestine, opening into the side of the 

 ceecum about an inch from its proximal ends. Its 

 walls have the structure of Peyer's patches. 



6. The caecum and vermiform appendix. 



The Cfecum is a large thin-walled diverticulum 

 of the alimentary canal, at the junction of the small 

 intestine and colon. It is about twenty inches long 

 and an inch or more in diameter, and is marked ex- 

 ternally by a spiral constriction which runs twenty 

 to thirty times round it. The small intestine opens 

 into the side of the caecum about an inch from 

 its proximal end ; a large Peyer's patch in the wall 

 of the caecum being continuous with the sacculus 

 rotundus. 



Proximally, the caecum passes directly into the 

 colon, while distally it ends blindly in the thick- 

 walled finger-like vermiform appendix. This latter 

 is about four inches long, and its walls resemble 

 Peyer's patches in appearance and structure. 



In the rabbit the cfBcum is of enormous size, as 

 in most herbivorous mammals with simple stomachs. 



7. The colon is about a foot and a half in length. The 



first part of it is very markedly sacculated, the 

 sacculations lying in three longitudinal rows, 

 separated by smooth areas of unequal width. 

 Towards the rectum the walls become smooth. 



8. The rectum or terminal portion of the intestine is a 



narrow tube, about two and a half feet in length, 

 pale in colour, and presenting a moniliform appear- 

 ance, owing to the contained faecal pellets. At its 

 hinder end it passes through the pelvic cavity to 

 the anus. 



