1378 CLINICAL AND TOPOGRAPHICAL ANATOMY 



The vermiform process (appendix) is developed at the apex of the caecum, 

 and persistence of the apical appendix of foetal type, is not uncommon. The 

 fact that all three tsenise coli converge at the base of the appendix is an anatomical 

 reminder of its primitive position. The anterior taenia is of great service in opera- 

 tions on the appendix, since by following it down from the colon the base of the 

 appendix can always be found. The adult position of the base of the appendix 

 on the postero-medial aspect of the caecum is due to the disproportionate growth 

 of the lateral saccule of the caecum which comes to form the apparent caecal apex. 



The appendix averages 10 cm. (4 in.) in length in the adult. The position of its base only 

 is at all constant. It lies distinctly below McBiu-ney's point, which is midway between the 

 umbilicus and the right anterior superior iliac spine. This point is often the seat of greatest 

 tenderness in appendicitis. The appendix itself may be found (1) pointing upward and to the 

 left toward the spleen, behind the terminal ileum and mesentery; (2) hanging over the pelvic 

 brim, in which position tenderness on rectal examination or pain on micturition results when 

 the organ is inflamed; (3) in the retro-colic fossa; and (4) with its tip projecting to the right of 

 the caecum in the right lateral paracolic fossa, where it causes tenderness when inflamed close 

 to the anterior superior iliac spine. The com-se and to some extent the gravity of abscesses 

 originating in the appendix will depend upon the position the inflamed organ is occupying at 

 the time of perforation. 



The artery of the appendix derived from the posterior branch of the ileo-colic reaches it by 

 running down behind the end of the ileum. It raises a fold of peritoneum called the mesen- 

 teriolum or mesoappendix. Very rarely the artery comes from the anterior branch of the 

 ileo-colic. 



The tcetiioe coli referred to above as converging on the base of the appendix contribute its 

 longitudinal muscular coat. The inner circular coat is thicker, but along the attachment of 

 the mesenteriole certain gaps for the passage of lymph and blood-vessels occur in the muscular 

 coats. Through these gaps infection may easily spread from the mucosa to the peritoneum 

 (Lockwood). 



The appendix is essentially a lymph gland and has been called the "abdominal tonsil." 

 The lymph follicles lie in the submucosa. They are poorly developed at bu-th but reach 

 their full development within the first few weeks of extra-uterine life (Berry).* Obliteration 

 of the lumen is common but is inflammatory in origin, and not, as was once thought, a change 

 normal in advanced age. 



Pericaecal fossae. — In addition to the mesentery of the appendix certain other folds of per- 

 itoneum are usually present at the ilfO-ca?cal junction: (1) the ileo-colic or anterior vascular 

 fold (fig. 1109) containing the anterior branch of the ileo-cohc artery; (2) the ileo-caecal, or 

 bloodless fold of Treves, running from the lower border of ileum onto the cajcum. The appen- 

 dix may be in a fossa behind either of these folds. It may also be found in the retro-colic fossa 

 lying behind the cajcum and commencement of ascending colon. 



The colon is readily distinguished from the small intestine by its three lon- 

 gitudinal taeniae and saccules and by the appendices epiploicae, which are devel- 

 oped before birth. 



The ascending colon runs with a slight lateral convexity upward from its 

 junction with the ciecum to the hepatic flexure which lies under the ninth 

 right costal cartilage at the level of the second lumbar vertebra and in contact 

 with the anterior surface of the right kidney and the lower surface of the right 

 lobe of the liver. It lies lateral to the right lateral vertical plane. This de- 

 scription is only true of an ascending colon examined by X-rays in the recumbent 

 position. AVhen the patient stantls up, the flexure sinks to the infracostal 

 plane (third lumbar vertebra) or even lower. As the colon ascends in the angle 

 iK'tween the ({uadratus lumborum and psoas, it also passes backward at an angle 

 of 51° with the horizontal, as may be seen in a sagittal section through the right 

 half of the abdomen (Coffey). f The caecum and ascending colon are distended 

 as a rule with fhiid contents and gas, and form the widest part of the colon. 



The variations in the peritoneal attachments of the colon, which are of growing clinical 

 importance, are explained l)y its mode (if development (p. 1179). During intra-uterine life 

 after rotation f)f the midgut round an axis formed by the sujierior mesenteric vessels, there is 

 a stage in wliich the colon has almost assumed its permanent position in the abdomen but is 

 .still [)rovi(le(l with a free mesocolon for both ascending and descending jiarts. This represents 

 the normal condition of (jujidrupcd mammals. In the normal human individual this stage is 

 transient, and before birth the ascending and descending colons lose their mesenteries by 

 fusion of the i)osterior layers with the parietal peritoneum. Meanwhile the great omentum, 

 formetl by a bulging out of the primitive dor.sal mesogastrium, fu.ses with the transverse colon 

 and it.s mesocolon. The extent of these i)rocesscs of fusion varies, i)articularly as far as the 

 a.sceiidirig and descending colons arc concerned. Thus only 52 per cent, of adults have neither 

 a.scending nor descending mesocolons (the normal condition). A mesocolon is found on the 

 left side in 30 j)er cent, of all cases and on the right side in 2G per cent. (Treves). In only a 



* Journ. Anat. and Phys., vol. 35, 1900, s;i. 



t .Surgery, Gynecology and Obstetrics, vol. 15, 1912, p. 390. 



