1 682 HUMAN ANATOMY. 



gous organ exists in some of the rodents and marsupials, but it is a long, tapering 

 caecum rather than an appendix strictly comparable to that of man. The appendix 

 is a vestige of the capacious caecum of some of the lower animals, or may be regarded 

 as a rudimentary caecum just as the human caecum is a rudiment of that found in the 

 herbivora or the rodents. Like other vestigial structures, or those which in the his- 

 tory of either the race or the individual have outlived their usefulness, it appears to 

 be of low. resistant power. This doubtless explains in part the special susceptibility 

 of the appendix to disease, as it does that of the uterus and the female breast 

 during the post-sexual period of life. 



2. Its mesentery — a fold made by the passage of the appendicular artery from 

 the ileo-colic at the back of the ileum to the appendix (page 1665) — is scanty; its 

 free border is shorter than the border applied to the appendix, and sometimes does 

 not extend much beyond its middle. The appendix, like the small intestine, is 

 therefore thrown into irregular curves or coils. Another peritoneal duplicature — the 

 ileo-caecal fold — runs from that part of the ileum most remote from its mesenteric 

 attachment and is united with the mesentery of the appendix. It carries no blood- 

 vessels of consequence, and is regarded by Treves as the remains of the true mesen- 

 tery of the appendix. It is interesting to note the fact that in the different types of 

 the human caecum those which involve a disproportionate growth of the caecum show 

 that it derives its peritoneal covering partly at the expense of the mesentery of the 

 appendix, which becomes more scanty and more vertical in direction the larger the 

 relative size of the caecum. The appendix moves directly with the caecum, but, 

 through the attachments of the meso-appendix to the caecum and to the mesentery 

 of the ileum, distention or displacement of those portions of the intestine makes trac- 

 tion upon it and causes increased curving or angulation. For these reasons, and on 

 account of the lessened interference with the blood-supply iinde infra), appendices 

 with exceptionally ample mesenteries extending to the tip of the organ are less fre- 

 quently the seat of disease and, when diseased, are less often found in a condition of 

 complete gangrene. 



3. The single artery supplying the appendix and running in the folds of the meso- 

 appendix, and its accompanying veins, are subjected to pressure by such traction, 

 or by the angulation of the organ itself, and various degrees of vascular obstruction and 

 congestion may result. The consequent oedema and swelling of the mucous mem- 

 brane aid the distortion of the appendix in causing interference with the escape of 

 the contents of the appendix into the caecum. After infection has started the vessels 

 are not infrequently occluded by septic thrombi. The peritoneal fold, which in the 

 female is often found running from the appendix to the broad ligament (page 1666), 

 may contain a second artery the presence of which has been offered as an explana- 

 tion of the relative infrequency of appendicitis in women. 



4. The disproportion between the length and the lumen of the appendix (16 

 to I, Finkelstein), the similar disproportion between the lumen and the area of the 

 secreting surface, its removal from the direct intestinal current, the feebleness of its 

 muscular walls, its dependent position, the absence or inefficiency of any valvular 

 arrangement at the appendiculo-caecal orifice, and the ease with which that orifice 

 may be diminished in size by oedema of the mucous membrane in its vicinity readily 

 explain the fact that under most circumstances in which drainage from the appendix 

 into the intestine would be desirable, it is apt to be lacking. Even a hyperaemic 

 catarrh from twists, kinks, or traction may in this way become the starting-point of 

 serious trouble, the successive steps of which might subsequently be retention of 

 mucus, epithelium, and fecal contents (possibly in the form of a concretion), 

 ulceration, parietal infection, or perforation or gangrene, and peritonitis, localized 

 or general. 



5. The abundance of lymphoid tissue in the appendix, as in the tonsils, favors 

 rapid swelling and infectious inflammations and aids in obstructing drainage. It may 

 to some extent account for these pathological conditions showing themselves during 

 the periods of growth and activity of the system much more frequently than in old 

 age, when the lymph-nodules in the walls of the intestinal canal become atrophied 

 (Struthers). In this connection it may be noted that other causes contributing to the 

 relative frequency of appendicitis in early life are (a) the susceptibility of children 



