^696 A MANUAL OF ANATOMY 



lower end, it receives the termination of the ileum, the opening 

 being guarded by the ileo-caecal valve. The position of this valve 

 corresponds with a point in the right spino-umbilical line between 

 i^ and 2 inches from the anterior superior iliac spine {McBurney's 

 point). In normal cases the caecum is very movable, being com- 

 pletely covered by peritoneum. The line of reflection of the 

 peritoneum posteriorly may correspond with the level of the ileo- 

 caecal orifice. In some cases, however, the peritoneum, after having 

 invested the posterior aspect of the caecum, gives a covering to the 

 posterior wall of the ascending colon for if inches (Treves), after 

 which the reflection takes place. The line of reflection may be 

 transverse or oblique, and the peritoneum so reflected is continuous 

 with the left or inferior layer of the mesentery proper. 



In a few cases (about 6 per cent.) the upper part of the posterior 

 surface of the caecum is destitute of peritoneum, and is bound 

 down by connective tissue to the subjacent fascia iliaca. Under 

 these circumstances its mobility is more or less curtailed. 



Varieties of Caecum. — The caecum is characterized by extreme variableness 

 as regards form, but the variations may be grouped into the following four 

 principal types (Treves) : 



First Type. — In the foetus the caecum is conical, the vermiform appendix 

 springing from the apex of the cone. The three longitudinal muscular 

 taeniae are disposed as follows : one is situated on the postero-internal aspect ; 

 a second lies along the postero-extemal aspect ; and the third is placed on 

 the anterior aspect. They are nearly equally distant from each other, and 

 meet at the apex of the caecum. 



Second Type. — The caecum is quadrilateral. The lower end presents two 

 sacculi, and the vermiform appendix springs from the interval between them. 

 The taeniae are situated as in the preceding type. 



Third Type. — In this variety the part of the caecum to the right ai the 

 anterior taenia becomes more developed, and consequently more prominent, 

 than the part to the left of that band, and the anterior wall undergoes greater 

 growth than the posterior wall. During these changes the apex is being 

 gradually shifted backwards and to the left, until finally it takes up a position 

 near the ileo-caecal junction, where it corresponds with the origin of the 

 vermiform appendix. The part to the right of the anterior taenia becomes 

 so much developed, especially in a downward direction, as to give rise to a 

 false apex. This is the most common form of caecum, the origin of the 

 appendix being transferred to the left and posterior aspect. 



Fourth Type. — In this variety the part to the right of the anterior taenia 

 undergoes excessive development, and the part to the left becomes much 

 atrophied, and in many cases practically disappears. This causes the anterior 

 taenia to terminate at the lower part of the ileo-caecal junction, and the 

 vermiform appendix arises immediately posterior to that point. 



Vermiform Appendix. — ^The vermiform appendix is a small 

 diverticulum of the caecum, which opens into its inner and back part 

 rather more than i inch below the ileo-caecal orifice. The caecal 

 end of the appendix is called its base, and the guide to it is rather 

 more than i inch below McBurney's point. Its diameter corre- 

 sponds with that of an ordinary goose-quill, and its length varies 

 from 2 to 6 inches, or more. Its outline is serpentine, and the 

 lumen is usually confined to its caecal half, though it may extend 

 throughout its entire length. The opening by which the appendix 



