This report is, in modified form, part of the thesis presented by Dr. Pace for his Ph.D. The work reported was done whilst he was a Commonwealth Scholar in the Department of Anatomy at the Middlesex Medical School, London. Contradictions exist in the literature as to whether the outer muscle coat of the human colon is complete or not. There are conflicting points of view as to the presence and extent of the longitudinal muscle in between the taeniae.  The material used consisted of 112 human colons, mainly postmortem, from subjects ranging in age from early fetal to 88 years. Portions from the named regions of the colon fixed in various states of distension were examined. The methods of microdissection were combined with those of histology. Sections, transverse of the whole circumference and longitudinal of the intertaenial wall, were studied. It was found that in the human colon the outer longitudinal coat, though thin in between the toenia, forms a complete and continuous layer. This is so at all ages, in all regions of the colon and in all states of distension except maximal when the muscle fascicles become separated by gaps filled in with connective tissue. Under no circumstances was the outer coat found to consist only of a few scattered longitudinal fibres and isolated bits of muscle, or to be entirely absent.peer-reviewe

Pace, Joseph L.

English

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108 THE ANATOMY OF THE MUSCLE WALL OF THE HUMAN COLON 1. The inter-ta:mial continuity of the longitudinal muscle coat J. L. PACE M.D. (MALTA), PH.D. (LOND.) Lecturer, Department of Anatomy, Royal University of Malta (This report is, in modified form, part of the thesis presented by Dr. Pace for his Ph.D.; the work reported was done whilst he was a Commonwealth Scholar in the Department of Anatomy at the Middlesex Medical School, London.) Introduction Contradictions exist in the literature as to whether the outer muscle coat of the human colon is complete or not. There are conflicting points of view as to the presence and extent of the longitudinal muscle in between the trenia::. Lowitz (1896) described the outer coat as forming a continuous layer and Rost (1912) positively asserted that there were longitudinal fibres forming a thin layer of muscle in the intertrenial regioas. Kelly and Herdon (1905), however, sug-gested that postnatally no longitudin.al muscle at all is to be found in between the trenia::; like Broman (1921), they des-cribed the outer coat as being continuous only up to. the time of birth when the pressure of the colonic contents causes the coat to split into three bundles between which the inner coat becomes exposed. Poirier and Charpy (1912), like Walmsley (1921), stated that the outer coat in between the trenire is almost hut not quite devoid of longitudinal fibres, there being isolated bits of muscle at these sites. A review of the more recent literature reveals similar conflicting statements. Thus, the outer muscle coat of the human colon is described as being: a) extremely thin between the tre-nire but complete (Hamilton 1946; Foster (1962). b) usually (Arey 1963) or to a cer-tain extent (Ham 1965) complete. c) occasionally interrupted (Bremer and Weatherford 1948; Deane et al. 1966) or partially deficient (N onidez and Windle 1953; Windel 1960). d) represented in between the tre-nice by only a few scattered longitudinal fibres (Wood Jones 1953; Golden 1949). Golden makes the point that it is the re-sultant weakness that allows the wall to bulge into haustra between the trenire. e) incomplete (Davenport 1966). Le Gros Clark (1965) states that the lon-gitudinal wall in between the trenice is entirely absent so that here the cir-cular muscle is exposed to the surface. Other authors appear to be of the same opinion but their statements are less emphatic. Hence the coat is described as being discontinuous (Bruce et al. 1964; Thorek 1962), as being in the form of and limited to the trenice (Bockus 1964; Hos-kins and Bevelander 1959; Magee 1962), or as failing entirely to surround the large bowel as it does in the small intestine (Anson and Maddock 1959; Bloom and Fawcett 1962; Grant and Basmajian 1965; Hollinshead 1962; Leeson and Leeson 1966). f) complete or otherwise according to circumstances. Lineback (1925) states that the outer coat, when contracted or moderately distended, form a distinct con-uous layer of longitudinal fibres and it is only with extreme distension that there may seem to be in some places no longi-tudinal fibres present. 109 Figure 1. Transverse section of mid-ascending colon (11 weeks fretus). . i The outer longitudinal layer of muscle (O.L.L.) forms a complete coat . a. x 150 Stain: Gomori. b. x 400 Stain: Mallory. 110 Figure 2. Transverse sec-tion of mid-pelvic colon (20 week fretus). The outer lon-gitudinal muscle layer (O.lL.L.) forms a complete coat ~md trenial thinckenings (T.) have appeared in it by the 20th week of fretal life. a. x 100: b. x 400: Stain: Mallory. Material and Methods The material used consisted of 112 human postmortem colons, with a few surgical specimens, ranging in age from 11 weeks fretal to 88 years. Portions from the different named regions of the colon, fixed in various states of distension, were used. The methods of microdissection wrre combined with those of histology. The intertcenial wall was examined under the dissecting microscope in an attempt ~o detect the presence and the continuity of the outer longitudinal coat at this site. Histological sections were cut as follows: transverse, of the whole circumference; longitudinal, of the intertcenial wall. Results In the human colon the outer coat though thin, forms a complete and con~ tinuous layer. This is so at all ages, in all 111 regions of the colon and, with some ex-ceptions, in all states of distension. The outer coat of the colon can be seen to form a continuous layer as early as. the 11th week of fretal Hife (Fig. 1): at thIS stage there are no tcenial thickenings and the outer coat consists of an extreme-ly thin layer, only one or two cells thick. The continuity of the outer coat can be seen more distinctly in a fretus of 20 weeks (Fig. 2) because the layer has now become slightly thicker and the tcenial thickenings quite marked. At the 7th fretal month, the tcenire are well marked and, in between, the outer layer is conti-nuous and uniformly thick, muscle fasci-culi being as yet inconspicuous. At 2 months postnatal (Fig. 3), however, the outer layer, which has now become rela-tively thick, no longer forms a uniform sheet because the muscle cells, both at the tcenice and in the inter-tcenial regions, are aggregated into fascicles: these fascicles Figu~e 3: Transverse section of mid-pelvic colon (infant, 2 months). The . long~tudInal mus~le forms a thick and complete coat consisting of fascIcles In contact wIth one another. a. x 15. Stain: Mallory. 112 are however in contact with one another and therefore maintain the continuity of the layer. With increasing age the muscle fascicles become better defined, but in later life they tend to flatten out; even so, the intertcenial longitudinal muscle fibres are still demonstrable in old age (Fig. 4) so that continuity of the layer is still maintained. It should be pointed out that there is some variation in the age at which these changes occur. Slight or moderate grades of disten-sion have no effect on the continuity of the outer coat of the colon. With maximal distension, the outer layer is still conti-nuous but the muscle fascicles become markedly flattened out and are occasion-ally separated from one another by quite appreciable gaps; these are filled in by the interfascicular connective tissue (Fig. 5). The fascicles of the tcenia also Jecome slightly separated from one an-Figure 4. Serosal surface of sigmoid colon (88 years) to include mesenteric (M) and antimesenteric trenire. a. The serosa has been dissected off to show the presence of inter-trenial longitudinal muscle fibres. b. The inter-trenial longitudinal mus-cle has been removed to reveal the underlying circular muscle coat. Scale: millimetres. other though gaps do not appear in between. Summary 1. Contradictions still exist in lite-rature as to whether the outer longitudi-nal muscle coat of the human colon is complete or not. 2. The material used consisted of 112 human colons, mainly postmortem, from subjects ranging in age from early fretal to 88 years. Portions from the named regions of the colon fixed in various states of distension were examined. 3. The methods of microdissection were combined with those of histology. Sections, transverse of the whole circum-ference and longitudinal of the intertreni,d wall, were studied. 4. It was found that in the human colon the outer longitudinal coat, though thin in between the tcenia, forms a com-plete and continuous layer. This is so at all ages, in all regions of the colon and in all states of distension except maximal 113 Figure 5. Transverse section of mid-transverse colon in maximal dis-tension. The outer muscle layer is continuous but the fascicles are sepa-rated by quite appreciable gaps (arrowed) filled in by connective tissue. a. 1 day p.:>stnatal x 7 b. 60 years Stain: Mallory. when the muscle fascicles become separ-ated by gaps filled in with connective tissue. Under no circumstances was the outer coat found to consist only of a few scattered longitudinal fibres and isolated bits oJ muscle, or to be entirely absent. x 400 References ANSON, B.]. and MADDOCK, \Y.G. (1959). Callan-der's Surgical Anatomy. 4th ed. \V.B. Saunders Co., Philadelph:a, London. AREY, L.B. (1963). Human Histology. 2nd ed. W.B. Saunders Co., Philadelphia, London. 114 BLOOM, W. and FAWCETT, D.\\'. (1962). A Text-book of Histology. 8th ed. W.B. Saunders Co., Philadelph:a, London. BocKus, H.L. (1964). Gastroenterology. 2nd ed. Vo!. 2. \V.B. Saunders Co., Philadelphia, London. BREMER, J.L. and WEATHERFORD, ILL. (1948). A Textbook of Hisology. McGraw-Hill Book Co., Illinois. BROMAl\, 1. (1921). 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A Manual of practical anatomy: a guide to the dissection of the human body. Part IT. Longmans,

A Textbook of Hisology.

AlimE;ntary Tract (Chapter 20) in: H:stology

Anatomy in Surgery.

Grant's Method of Anatomy.

Hewer's Textbook of Histology' for Medical students. 8th ed.

Human Histology. 2nd ed.

Phys;ology of the digestive tract: an introductory text. 2nd ed.

Recherches sur I'appareil musculaire du gros intestin chez I'homme et quelques mammiferes. Bordeaux Thes;s

Roentgen-Ray examination of the digest:ve tract.

Textbook of Anatomy. Harper and Row,

Textbook of Histology. 3rd ed.

The inter-ta:mial continuity of the longitudinal muscle coat

The Large Intest:ne and Defaecation. (Chapter I1). in Gastrointestlnal Physiology.

The vermiform appendix and its diseases.

Traite d'Anatomie Humaine.

The anatomy of the muscle wall of the human colon : the inter-taenial continuity of the longitudinal muscle coat

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The anatomy of the muscle wall of the human colon : the inter-taenial continuity of the longitudinal muscle coat

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