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THE CAtCUM AND APPENDIX. 1027 
telescoping of the small into the large intestine: it must be added that the 
peritoneum and longitudinal muscular fibres of the bowel take no part in this 
infolding ; on the contrary, they are stretched tightly across the crease produced on 
the exterior by the inversion, and thus serve to preserve the fold and the formation 
of the valve. 
As seen from the interior, in specimens which have been distended and dried 
(Fig. 693), the valve is made up of two crescentic segments—an upper, In a more 
or less horizontal plane, forming the superior margin of the aperture; and a lower, 
which is also larger, placed in an oblique plane, and sloping upwards and inwards 
(1.e. towards the cav ity of the cecum). Between the two segments is situated the 
slit-shaped opening, which runs in an almost antero-posterior direction, with a 
rounded anterior and a pointed posterior extremity (Fig. 695). At each end of 
the orifice the two segments of the valve meet, unite, and are then prolonged 
around the wall of the cavity as two prominent folds —the frenula (frenula 
valvule coli). It is thought that when the cecum is distended, and its cireum- 
ference thereby increased, these frenula are put on the stretch, and, pulling upon 
the two segments of the valve, they bring them into apposition, and effect the 
closure of the orifice. 
The position of the ileo-cecal orifice, in the average condition, may be indicated 
on the surface of the body by the point of inte section of the intertubercular and 
Poupart lines. A point 1 to 14 inches (2°5 to 3-7 cm.) lower eleva would correspond 
to. the orifice of the vermiform process. 
In bodies hardened in situ with formalin, the valve and orifice present an entirely different 
appearance (see Fig. 694, in which three different forms of hardened valves are shown), suggesting, 
much more closely than in the dried state, the appearance of telescoping or inversion mentioned 
above. In them also the two segments of the valve are much thicker and shorter, but they can 
always be distinguished, and are found to bear the same relation to one another as in the dried 
condition, although this may be obscured by foldings or ruge. The aperture may be slit-like or 
rounded, with sloping or infundibuliform edges ; the frenula are not so prominent at times; but 
the whole valve projects much more abruptly into the cavity of the cecum than in the diste nded 
and dried specimen. 
Structure of the Ileo-czcal Valve.—Each segment of the valve is formed of an 
infolding of all the coats of the gut, except the peritoneum and the longitudinal muscular 
fibres, and consequently it consists of two layers of mucous membrane, with the sub- 
mucosa and the circular muscular fibres between, all of 
which are continuous with those of the ileum on the one 
hand and of the large intestine on the other. The surface 
of each segment turned towards the small intestine is 
covered with villi, and conforms in the structure of its 
mucous membrane to that of the ileum ; whilst the mucous F 
membrane of the opposite side resembles the mucous coat < MUCOUS MEMBRANE 
of the large bowel. 
PERITONEUM 
LONGITUDINAL MUSC. FIBRES 
“ CIRCULAR 
, 
In the dried specimen the upper segment usually projects 
further into the cavity of the cecum than the lower, so that 
the aperture appears to be placed between the edge of the 
lower segment and the under surface of the upper. 
There is little doubt, as pointed out by Symington, that 
the efficiency of the ileo-ciwecal valve is largely due to the 
oblique manner in which the ileum enters or invaginates the 
cecunr; this oblique Desa alone, as in the case of the ureter 
piercing the wall of the bladder, would probably be sufficient 
to prevent a return of the cecal contents. ‘In the great 
majority of cases, when in position within the body, the lem = 
is perfectly protected from such a return, although when the Hye 
parts are removed, and then distended with fluid, this often : 
CAECUM 
695.— DIAGRAMMATIC SECTION 
THROUGH THE JUNCTION OF ILEUM 
passes through the valve, and reaches the small intestine. Witt’ CRCUM. do. SHOW! ain 
Still, the efficiency of such a test, applied when the parts FORMATION OF THE ILEO-CKCAL 
are deprived of their natural supports, cannot be relied upon. VALVE, 
The size of the segments of the valve, as seen in the dried 
condition, varies considerably ; they are sometimes very imperfect ; and even the absence of both 
has been recorded. But here again there is danger of falling into error, through examining 
the parts under such artificial conditions. 
Development of Cecum and Appendix.—The ciecum first appears in the embryo, at about 
