852 THE INTESTINE. 



which greatly exceeds that of the small intestine, varies at different points 

 from two inches and a half to about one inch and a half. It diminishes 

 gradually from its commencement at the csecum to its termination at the 

 anus; excepting that there is a well-marked dilatation of the rectum just 

 above its lower end. 



In outward form, the greater part of the large intestine differs remarkably 

 from the small intestine ; for, instead of constituting an even cylindrical 

 tube, its surface is thrown into numerous sacculi, marked off from each other 

 by intervening constrictions, and arranged in three longitudinal rows, sepa- 

 rated by three strong flat bands of longitudinal muscular fibres. This saccu- 

 lated structure is not found in the rectum. 



For the sake of convenience, the description of the rectum will be reserved 

 till that of the rest of the great intestine is completed. 



The C^CUM. The intestinum csecum, or caput caecum coli, is that part 

 of the large intestine which is situated below the entrance of the ileum. Its 

 length is about two inches and a half, and its diameter nearly the same : it 

 is the widest part of the large intestine. 



The csecum is situated in the right iliac fossa, immediately behind the an- 

 terior wall of the abdomen. It is covered by the peritoneum in front, below, 

 and at the sides : but behind it is usually destitute of peritoneal covering, 

 and is attached by areolar tissue to the fascia covering the right iliacus 

 muscle. In this case the csecum is comparatively fixed ; but in other in- 

 stances the peritoneum surrounds it almost entirely, and forms a duplicature 

 behind it, called meso-cczcum. 



Proceeding from the inner and back part of the csecum, at its lower end, 

 is a narrow, round, and tapering portion of the intestine, named the appendix 

 cceci, or appendix vermiformis. The width of this process is usually about 

 that of a large quill or rather more, and its length varies from three to six 

 inches, these dimensions differing much in different cases. Its general direc- 

 tion is upwards and inwards behind the csecum ; and after describing a few 

 slight turns it 'ends in a blunt point. It is retained in its position by a small 

 fold of peritoneum, which forms its mesentery. The csecal appendix is hol- 

 low as far as its extremity : and its cavity communicates with that of the 

 csecum by a small orifice, sometimes guarded by a valvulvar fold of mucous 

 membrane. 



This appendix is peculiar, as far as is known, to man and certain of the 

 higher apes, and to the wombat ; but in some animals, as in the rabbit and 

 hare, the distal part of the csecum, being diminished in diameter and highly 

 glandular, may represent a condition of the appendix. 



Ileo-ccecal or ileo-colic valve. The lower part of the small intestine, as- 

 cending from left to right, and from before backwards, enters the commence- 

 ment of the large intestine, with a considerable degree of obliquity, about 

 two inches and a half from the bottom of the csecum, and opposite the junc- 

 tion of the latter with the ascending colon. The opening leading from the 

 ileum into the large intestine is guarded by a valve composed of two seg- 

 ments or folds. This is the ileo-cmcal or ileo-colic valve: it is also called the 

 valve of Bauhin and the valve of Tulpius, though Fallopius had described it 

 before either of those anatomists. 



The entrance between the two segments of the valve is a narrow elongaied 

 aperture, lying nearly transverse to the direction of the great intestine. 

 The anterior end of this aperture, which is turned forwards and slightly to 

 the left, is rounded, but the posterior end is narrow and pointed. It is 

 bounded above and below by two prominent semilunar folds, which project 



