THE INTESTINAL CANAL. 1033 



mesentery or abdominal wall when it is still high up beneath the liver, the caecum 

 will drag it down in an inverted position. If no such adhesions occur, then it 

 will descend freely, and perhaps dip into the pelvis. It takes a somewhat spiral 

 form, due to its short mesentery. 



/!< lotions to ccecum have been noted above under Caecum, where the data are 

 quite constant. 



Relations to the anterior abdominal wall for clinical purposes do not agree. 

 Clado draws two lines, one along the outer edge of the right Rectus, and another 

 connecting the anterior superior spines of the ilia. The point where these inter- 

 sect Clado" uses as a guide to the base of the appendix, which brings it into the 

 hypogastrium. McBurney draws an imaginary line from the right anterior supe- 

 rior spine to the umbilicus. His ''point" is situated on this line two inches from 

 the spine. This is used as a guide to the base of the appendix. This point is in 

 the right iliac fossa. 



Relations to peritoneum are that a mesentery is always present, but it does 

 not extend the whole length of the tube, leaving the distal third or so free and 

 completely covered by peritoneum. This meso-appendix is triangular and comes 

 from the left leaf of the mesentery, and contains in its fold the posterior branch 

 of the ileo-caecal artery, which is derived from the ileo-colic. 



Its walls present the same layers as seen in the colon, and its whole mucous 

 membrane is closely studded with solitary glands. It is usually hollow to its 

 extremity and its lumen communicates with the caecum by a small orifice often 

 guarded by a valve. 



Gerlach in 1847 described a " semilunar fold of mucous membrane guarding 

 the appendico-caecal orifice." It was only .5 to 1 mm. high and was so turned as 

 to cause retention of the normal secretion in the appendix. The existence of 

 Gerlach's valve is now doubted. It is inconstant and unimportant. 



There is usually another bigger crescentic fold near the orifice (Fig. 654), but 

 with no function of a valve. 



According to Ribbert and Zuckerkandl the cavity of the vermiform appendix 

 tends to undergo obliteration, not as a pathological process, but a physiological 

 one. In children the lymph-follicles of the appendix are very numerous and close. 

 After the twentieth or thirtieth year it is normal for them to atrophy. Oblitera- 

 tion of the process occurs to some degree in 99 cases out of 400 (25 per cent,) ; 

 total obliteration in 3.5 per cent. (Ribbert). Or obliteration occurred in 23.7 per 

 cent. ; total obliteration in 13.8 per cent., and partial (distal half most common) 

 in 9.9 per cent. (Zuckerkandl). It never occurs in new-born. After sixty years 

 of age more than half are obliterated. It occurs more often in a short process, 5 

 to 6 cm. long. One can never tell by macroscopic appearance as to the presence 

 of obliteration. 



The pathology seems to be an involution-change in a functionless organ. 

 There are no signs of inflammation or cicatrices. As a first step there is atrophy 

 of the mucous membrane, and its glands disappear. The submucosa thickens and 

 accumulates fat. The muscular coat is either unchanged or becomes hypertro- 

 phied. The adenoid tissue is finally lost. There are four authentic cases of 

 absence of the appendix. For the fossce of this region see p. 997. 



The Ileo-colic, Ileo-caecal valve or Valvula Bauhini. 



The end of the ileum passes obliquely upward and to the right, and opens 

 into the large intestine on its postero-internal surface ; it opens upon the summit 

 of a plica sigmoidea which marks the junction between the caecum and ascending 

 colon. 



This orifice appears as a transversely oblique or a double convex slit. It is 

 often rounded on the left and presents a sharp apex to the right (Fig. 654). It- 

 is bounded by a valve having two semilunar segments, a colic and a caecal one, 

 which project into the lumen of the large intestine. The upper of these seg- 

 ments is more horizontal, the lower more concave and longer. At each end they 



