96 STUDIES IN PHYSIOLOGY 



9. THE LARGE INTESTINE 



Position, Form, Size. The large intestine is the last por- 

 tion of the alimentary canal. It is a tube 'five or six feet 

 long, with a diameter gradually decreasing from two and 

 a half or three inches to an inch at its lower end. Beginning 

 in the lower right-hand region of the abdominal cavity as a 

 saclike pouch called the cm' cum (Latin caecum = blind sac) 

 (Fig. 23), the large intestine passes anteriorly on the right 

 side (the ascending colon) to the lower surface of the stom- 

 ach ; it then crosses the abdominal cavity (transverse colon) ; 

 a third portion (the descending colon) runs posteriorly on 

 the left side. The large intestine then takes an S-shaped 

 course (sigmoid flexure) and passes to the exterior of the 

 body by a short, straight tube, the rectum (Latin rectus = 

 straight). 



Ileo-caecal Valve. The final portion of the small intestine 

 (called the il'e-um) opens into the side of the large intestine 

 in the region of the caecum by a so-called il-eo-cce'cal orifice. 

 This is guarded by two flaps of membrane. The food can 

 pass into the large intestine, but its return to the small in- 

 testine is prevented by this double-flapped ileo-ccecal valve, 

 which works on the same principle as the valve in a bicycle 

 tire; after air has been forced into the tire, the valve 

 immediately closes to prevent its escape. 



Vermiform Appendix. Connected with the caecum is a 

 small tubelike sac about the size of a pencil, and usually 

 about four inches long (Fig. 23). From its more or less 

 twisted shape it has received the name ver'mi-form ap-pen'dix 

 (Latin vermiform = worm-shaped). The appendix of rab- 

 bits (see Fig. 4, P) and of several other herbivorous animals 

 is of considerable use in the process of absorption. In man, 

 however, it has lost this importance, and remains as a small 

 and probably useless extension of the caecum. Ap-pend-i- 

 ci'tis is a diseased condition arising from inflammation in 

 the tissues of the appendix.. 



