41
J. Anat. (1991), 177, pp. 41-46 With 4 figures Printed in Great Britain
The peritoneal elastic lamina* P. J. T. KNUDSEN Institute of Pathology, Aalborg Sygehus, DK 9000 Aalborg, Institute of Pathological Anatomy, Hjorring Sygehus, DK 9800 Hjorring, and Institute of Forensic Medicine, University of Aarhus, DK 8000, Aarhus C, Denmark
(Accepted 7 January 1991) INTRODUCTION
The peritoneal elastic lamina (lamina elastica peritonei, LEP) is a little-known component of the peritoneum, being composed of a network of elastic fibres situated immediately beneath the basement membrane of the peritoneal mesothelium, separated from this by a scanty layer of connective tissue, poor in collagen fibres. The LEP as a separate entity has been referred to only rarely (Morson & Dawson, 1979; Dobbie, Zaki & Wilson, 1981). A similar structure has been described in animals (Rhodin, 1974; Parsons, Marko & Wansor, 1983), but no precise description of the extent of this structure in man is available. Since it might prove useful, both for normal anatomical and for pathoanatomical studies, it was decided to undertake a systematic study by light microscopy. MATERIAL AND METHODS
In order to demonstrate the extent of the LEP, samples were removed from 10 consecutive patients who had died without antemortem evidence of intra-abdominal disease, and whose abdominal cavity was normal at autopsy. An attempt was made to remove the samples as soon as possible after death, but observance of Danish law meant, for all practical purposes, an interval of at least 6 hours. Samples were taken from the peritoneal covering of all intraperitoneal and retroperitoneal organsstomach, small and large intestine, appendix, liver, spleen, gall bladder, pancreas, uterus and fallopian tubes as well as from the parietal peritoneum on both sides above and below the navel, the diaphragm and the testis. Sections were taken perpendicular to the peritoneal surface from the samples from the parietal peritoneum and the intestines. Selected sections were also cut at a right angle to these, parallel to the plane of the fibres of the LEP so that they were vizualised 'en face'. Following paraffin embedding, the sections were submitted to a variety of elastic stains, Weigert's or Verhoefls stains with or without Van Gieson Hansen counterstain being used routinely, supplemented by Orcein or Victoria Blue as required. Because of the state of preservation of the autopsy samples, a supplementary series of slides from grossly normal areas of organs covered with peritoneum removed at operation stomach, small and large intestine, appendix, spleen, gall bladder, testis, uterus and the fallopian tubes-was investigated. The organs examined in this series were removed either because of disease in the vicinity, for technical reasons or * Reprint requests to Dr Peter J. T. Knudsen, Institute of Forensic Medicine, University of Aarhus, Finsensgade 15, DK 8000, Aarhus C, Denmark.
42
P. J. T. KNUDSEN
following trauma. The operation samples were stained in the same way as those from the autopsy cases. RESULTS
In sections cut parallel to the plane of the fibres of the LEP, it was found that the layer consisted of elastic fibres running at various angles to each other (Fig. 1). Frequently a dominant direction could be demonstrated, but this was not very consistent, and no reliable indication of a dominant direction for any one organ was found. In the serosa of the stomach, the wall of which contains large amounts of elastic tissue, an elastic layer consistent with the LEP was found, most distinct in areas where fatty tissue or connective tissue separated the serosa from the external muscular layer (Fig. 2). This was discernible only with difficulty where the serosa lay immediately adjacent to the musculature. At sites where a transition between the two was found, such as where ligaments are attached to the stomach wall, the LEP could easily be followed from them into the serosa of the stomach. The LEP was easily demonstrated in every section in the small as well as in the large intestine (Figs 3 and 4), as was to be expected from previous observations (Morson & Dawson, 1979). By extending the sections from the intestinal wall along the mesentery it was seen that the LEP did not encircle the intestine, but could be followed all the way to the posterior abdominal wall, where it continued as part of the parietal peritoneum. The LEP of the small intestine in particular was a very well-defined structure, consisting of quite thick elastic fibres running in parallel with thinner fibres connecting them. The main direction was subject to considerable variation. In the appendix a very delicate LEP was found, behaving exactly like that of the large intestine, i.e. in continuity with that of the mesenteriolum appendicis and not making a complete circle. In the liver and spleen, both of which have a thick covering of connective tissue containing elastic tissue as one of its main components, the LEP was indistinguishable, but at the attachments of both organs, where the connective tissue ligaments blend into the capsule, the LEP could easily be followed as it separated itself from the many layers of elastic and connective tissue and continued as a single layer of elastic tissue, similar to that seen in the intestine. In the wall of the gall bladder, however, which is composed of a much looser connective tissue, the LEP was found under the mesothelium as in the intestines, and could be followed as the peritoneum was reflected to the surface of the liver. The pancreas, situated retroperitoneally, behaved quite like the intraperitoneal organs. The LEP was remarkably easy to find, even in the autopsy cases where considerable autolysis was seen. The nonpregnant uterus and the fallopian tubes were very similar to the liver and spleen, the LEP being hard to distinguish on the organ Fig. 1. Left. The elastic fibres of the mesentery in plan view, showing a general longitudinal orientation of the thicker fibres. Verhoeff's elastic stain x 180. Fig. 2. Right. The elastic fibres of the serosa of the stomach at the attachment of one of the ligamentous folds of the peritoneum. Note that the fibres follow the surface, not the muscle layers of the stomach. Orcein x 90. Fig. 3. Left. The very well developed elastic layer of the small intestine forming a near continuous band in the serosa. Orcein x 180. Fig. 4. Right. The attachment of the mesocolon to the colon. The elastic layer is seen to continue from the intestinal serosa into the mesentery, leaving the area between the attachments without a circular elastic layer. Weigert's elastic stain x 90.
Peritoneal elastic lamina
43
2
x
t.h
P
A; :;t
tt Ib
'is.:.
Figs. 14. For legend see opposite.
(4
P. J. T. KNUDSEN 44 proper, but easily found in the attachments. Finally, the bladder displayed a prominent LEP in the peritoneal covering. The parietal peritoneum was sampled widely, since nothing was known previously as to the LEP in the parietal peritoneum. All the samples displayed a well-demarcated LEP, with no predilection for particular sites as to the shape, direction or size of the fibres. The testes are intraperitoneal in origin but in descending take with them a part of the investing peritoneum, the tunica vaginalis. Accordingly samples were taken to investigate whether the elastic layer of the peritoneum was part of the tunica vaginalis. In the sections a similar elastic tissue was found, scant but consistent. For comparison random samples were removed from the pleura and the pericardium. A similar elastic layer is known to exist there and was very easy to demonstrate, especially in the pleura. DISCUSSION
While elastic tissue has been studied intensively in some parts of the body both in normal subjects and in some disease states, such as in vessel walls, the lungs, and in the breast in patients with carcinoma, the elastic tissue of the peritoneum has not been the subject of very great interest. The presence of elastic tissue in the peritoneum was noted in studies of the gastrointestinal tract at the end of the nineteenth and in the beginning of twentieth century (Dobbertin, 1896; Legge, 1897; Livini, 1899; Patzelt, 1936), but the existence of a distinct membranous or reticular structure in the peritoneum of man, analogous to that of the pleura (Spencer, 1977; Thomas, 1987) or of the pericardium (Ferrans, Ishihara & Roberts, 1982; Thomas, 1987), has only been noted by few, and no systematic study of the topographical distribution of the structure has previously been undertaken. In animals, however, the presence of elastic tissue beneath the mesothelium of the peritoneum has been described (Rhodin, 1974) and its presence has been used for experimental purposes (Parsons et al. 1983). While the elastic tissue in the peritoneum of man has been mentioned mainly in the intestinal
serosa (Morson & Dawson, 1979), its alleged presence in the human parietal peritoneum (Seifert, 1927) has only once been convincingly demonstrated (Dobbie et al. 1981; Thomas, 1987). The investigations described in this paper are concerned mainly with the topography of the LEP, because the acceptance of the presence of the structure as a normal anatomical entity is the prerequisite for its use in experimental and clinical work. The LEP is found ubiquitously in the visceral and parietal peritoneum, but developed to a variable extent, according to the properties of the organ it covers. As may be expected, the LEP is most prominent in organs in which a considerable and rapid change of volume takes place, as in the intestines and the gall bladder, while it is less prominent or discernible only with difficulty in static or nearly static organs such as the uterus, appendix, liver, spleen, etc. It is worth noting, however, that at the attachments of peritoneum, the LEP is easily demonstrated. It can, for example, be followed from the parietal peritoneum of the posterior abdominal wall, along the ligaments of the porta hepatis or the spleen until it merges with the copious elastic tissue of their capsules. The stomach is in an intermediate category, being an organ with large variations in size and shape; but as the serosa covering the stomach is scanty, and the elastic tissue of the stomach wall plentiful, the LEP may be hard to demonstrate. As is the case with the liver and the spleen, the peritoneal attachments at the lesser and greater curvatures
45 Peritoneal elastic lamina consistently display an LEP and by following it from there, it may be seen to continue into the serosa of the stomach. In the parietal peritoneum the LEP may be followed from the intestinal serosa along the mesentery to the abdominal wall, as has been illustrated in animals (Rhodin, 1974). It can be found all over the parietal peritoneum, which may have significance for those making peritoneal biopsies. For normal anatomical purposes the LEP is useful, since we can now safely assume that the peritoneum includes LEP. The LEP should also be useful for clinical work. It may provide a baseline for measuring the thickness of the peritoneum in various irritative conditions, for example, in patients undergoing continuous ambulatory peritoneal dialysis (CAPD), or it might give an indication of the extent of metastases within the abdominal cavity. Knowledge of the LEP might be useful for studies of transport of particulate matter across the peritoneum (Parsons, Marko, Braun & Wansor, 1982; Parsons, Marko, Rademacher & Frank, 1985). In relation to nomenclature, it seems preferable for the present to retain the nonspecific term lamina or layer, permitting a more precise term to be devised later. SUMMARY
The structure and extent of the submesothelial elastic tissue of the peritoneum, tentatively termed the peritoneal elastic lamina (lamina elastica peritonei, LEP), was studied in autopsy and biopsy material by light microscopy. The investigation confirms the presence of a well-defined network of elastic fibres just beneath the basement membrane of the visceral and parietal peritoneum in man. The LEP is claimed to be analogous to similar elastic tissue in other serosal cavities, the pleura and the pericardium, as previously described. The LEP may be useful for normal anatomical as well as pathoanatomical investigations. The inspiration and support of my senior colleagues at the Institutes, particularly Dr Peter Stubbe Teglbjaerg, Aalborg Hospital, the technical assistance of Mrs K. Ugilt, Hj0rring Hospital, and the photographic assistance of Mrs A. Dalmose and Mr S. Shapiro, Aarhus Municipal Hospital, are gratefully acknowledged. This study was previously presented in part at the PAX-Conference on Peritoneal Access, Lund, Sweden, in June 1987. REFERENCES
DOBBERTIN, R. (1896). Ober die Verbreitung und Anordnung des elastischen Gewebes in den Schichten des gesamten Darmkanals. Rostock: Universitats-Buchdruckerei von Adler's Erben. DOBBIE, J. W., ZAKI, M. & WILSON, L. (1981). Ultrastructural studies on the peritoneum with special reference to chronic ambulatory peritoneal dialysis. Scottish Medical Journal 26, 213-223. FERRANS, V. J., IsHIHARA, T. & ROBERTS, W. C. (1982). Anatomy of the pericardium. In Pericardial Disease (ed. P. S. Reddy, D. F. Leon & J. A. Shaver), pp. 15-29. New York: Raven Press. LEGGE, F. (1897). Sulla distribuzione topografica dellefibre elastiche nelrapparecchio digerente. Cagliari: Tip. Muscas di P. Valdes. LIVINI, F. (1899). Sulla distribuzione del tessuto elastico in varii organi del corpore umano. Monitore Zoologico Italiano 10, 12-23. MORSON, B. C. & DAWSON, I. M. P. (1979). In Gastrointestinal Pathology, pp. 228 and 492. Oxford: Blackwell. PARSONS, D. F., MARKO, M., BRAUN, S. J. & WANSOR, K. V. (1982). Ascites tumor invasion of mouse peritoneum studied by high-voltage electron microscope stereoscopy. Cancer Research 42, 4574-4583. PARSONS, D. F., MARKO, M., RADERMAcHER, M. & FRANK, J. (1985). Shape changes and polarization of cells migrating through tissue. A high-voltage electron microscope and computer graphics study of serial thick sections. Tissue and Cell 17, 491-510.
46
P. J. T. KNUDSEN
PARSONS, D. F., MARKO, M. & WANSOR, K. (1983). Elastic reticulum and collagen of normal mouse peritoneum. Micron 14, 1-10. PATZELT, V. (1936). Der Darm. In Verdauungsapparat, Handbuch der mikroskopischen Anatomie des Menschen (ed. W. von Mollendorf), Part 3, pp. 292-296. Berlin: Springer. RHODIN, J. A. G. (1974). In Histology; A Text and Atlas, p. 576. London: Oxford University Press. SEIFERT, E. (1927). Peritoneum einschliesslich Netz. In Verdauungsapparat, Handbuch der mikroskopischen Anatomie des Menschen (ed. W. von Mollendorf), Part 1, pp. 337-360. Berlin: Springer. SPENCER, H. (1977). In Pathology of the Lung, p. 77. Oxford: Pergamon Press. THOMAS, N. W. (1987). Embryology and structure of the mesothelium. In Pathology of the Mesothelium (ed. J. S. P. Jones). Berlin, Heidelberg: Springer.
J. Anat. (1991), 177, pp. 41-46 With 4 figures Printed in Great Britain
The peritoneal elastic lamina* P. J. T. KNUDSEN Institute of Pathology, Aalborg Sygehus, DK 9000 Aalborg, Institute of Pathological Anatomy, Hjorring Sygehus, DK 9800 Hjorring, and Institute of Forensic Medicine, University of Aarhus, DK 8000, Aarhus C, Denmark
(Accepted 7 January 1991) INTRODUCTION
The peritoneal elastic lamina (lamina elastica peritonei, LEP) is a little-known component of the peritoneum, being composed of a network of elastic fibres situated immediately beneath the basement membrane of the peritoneal mesothelium, separated from this by a scanty layer of connective tissue, poor in collagen fibres. The LEP as a separate entity has been referred to only rarely (Morson & Dawson, 1979; Dobbie, Zaki & Wilson, 1981). A similar structure has been described in animals (Rhodin, 1974; Parsons, Marko & Wansor, 1983), but no precise description of the extent of this structure in man is available. Since it might prove useful, both for normal anatomical and for pathoanatomical studies, it was decided to undertake a systematic study by light microscopy. MATERIAL AND METHODS
In order to demonstrate the extent of the LEP, samples were removed from 10 consecutive patients who had died without antemortem evidence of intra-abdominal disease, and whose abdominal cavity was normal at autopsy. An attempt was made to remove the samples as soon as possible after death, but observance of Danish law meant, for all practical purposes, an interval of at least 6 hours. Samples were taken from the peritoneal covering of all intraperitoneal and retroperitoneal organsstomach, small and large intestine, appendix, liver, spleen, gall bladder, pancreas, uterus and fallopian tubes as well as from the parietal peritoneum on both sides above and below the navel, the diaphragm and the testis. Sections were taken perpendicular to the peritoneal surface from the samples from the parietal peritoneum and the intestines. Selected sections were also cut at a right angle to these, parallel to the plane of the fibres of the LEP so that they were vizualised 'en face'. Following paraffin embedding, the sections were submitted to a variety of elastic stains, Weigert's or Verhoefls stains with or without Van Gieson Hansen counterstain being used routinely, supplemented by Orcein or Victoria Blue as required. Because of the state of preservation of the autopsy samples, a supplementary series of slides from grossly normal areas of organs covered with peritoneum removed at operation stomach, small and large intestine, appendix, spleen, gall bladder, testis, uterus and the fallopian tubes-was investigated. The organs examined in this series were removed either because of disease in the vicinity, for technical reasons or * Reprint requests to Dr Peter J. T. Knudsen, Institute of Forensic Medicine, University of Aarhus, Finsensgade 15, DK 8000, Aarhus C, Denmark.
42
P. J. T. KNUDSEN
following trauma. The operation samples were stained in the same way as those from the autopsy cases. RESULTS
In sections cut parallel to the plane of the fibres of the LEP, it was found that the layer consisted of elastic fibres running at various angles to each other (Fig. 1). Frequently a dominant direction could be demonstrated, but this was not very consistent, and no reliable indication of a dominant direction for any one organ was found. In the serosa of the stomach, the wall of which contains large amounts of elastic tissue, an elastic layer consistent with the LEP was found, most distinct in areas where fatty tissue or connective tissue separated the serosa from the external muscular layer (Fig. 2). This was discernible only with difficulty where the serosa lay immediately adjacent to the musculature. At sites where a transition between the two was found, such as where ligaments are attached to the stomach wall, the LEP could easily be followed from them into the serosa of the stomach. The LEP was easily demonstrated in every section in the small as well as in the large intestine (Figs 3 and 4), as was to be expected from previous observations (Morson & Dawson, 1979). By extending the sections from the intestinal wall along the mesentery it was seen that the LEP did not encircle the intestine, but could be followed all the way to the posterior abdominal wall, where it continued as part of the parietal peritoneum. The LEP of the small intestine in particular was a very well-defined structure, consisting of quite thick elastic fibres running in parallel with thinner fibres connecting them. The main direction was subject to considerable variation. In the appendix a very delicate LEP was found, behaving exactly like that of the large intestine, i.e. in continuity with that of the mesenteriolum appendicis and not making a complete circle. In the liver and spleen, both of which have a thick covering of connective tissue containing elastic tissue as one of its main components, the LEP was indistinguishable, but at the attachments of both organs, where the connective tissue ligaments blend into the capsule, the LEP could easily be followed as it separated itself from the many layers of elastic and connective tissue and continued as a single layer of elastic tissue, similar to that seen in the intestine. In the wall of the gall bladder, however, which is composed of a much looser connective tissue, the LEP was found under the mesothelium as in the intestines, and could be followed as the peritoneum was reflected to the surface of the liver. The pancreas, situated retroperitoneally, behaved quite like the intraperitoneal organs. The LEP was remarkably easy to find, even in the autopsy cases where considerable autolysis was seen. The nonpregnant uterus and the fallopian tubes were very similar to the liver and spleen, the LEP being hard to distinguish on the organ Fig. 1. Left. The elastic fibres of the mesentery in plan view, showing a general longitudinal orientation of the thicker fibres. Verhoeff's elastic stain x 180. Fig. 2. Right. The elastic fibres of the serosa of the stomach at the attachment of one of the ligamentous folds of the peritoneum. Note that the fibres follow the surface, not the muscle layers of the stomach. Orcein x 90. Fig. 3. Left. The very well developed elastic layer of the small intestine forming a near continuous band in the serosa. Orcein x 180. Fig. 4. Right. The attachment of the mesocolon to the colon. The elastic layer is seen to continue from the intestinal serosa into the mesentery, leaving the area between the attachments without a circular elastic layer. Weigert's elastic stain x 90.
Peritoneal elastic lamina
43
2
x
t.h
P
A; :;t
tt Ib
'is.:.
Figs. 14. For legend see opposite.
(4
P. J. T. KNUDSEN 44 proper, but easily found in the attachments. Finally, the bladder displayed a prominent LEP in the peritoneal covering. The parietal peritoneum was sampled widely, since nothing was known previously as to the LEP in the parietal peritoneum. All the samples displayed a well-demarcated LEP, with no predilection for particular sites as to the shape, direction or size of the fibres. The testes are intraperitoneal in origin but in descending take with them a part of the investing peritoneum, the tunica vaginalis. Accordingly samples were taken to investigate whether the elastic layer of the peritoneum was part of the tunica vaginalis. In the sections a similar elastic tissue was found, scant but consistent. For comparison random samples were removed from the pleura and the pericardium. A similar elastic layer is known to exist there and was very easy to demonstrate, especially in the pleura. DISCUSSION
While elastic tissue has been studied intensively in some parts of the body both in normal subjects and in some disease states, such as in vessel walls, the lungs, and in the breast in patients with carcinoma, the elastic tissue of the peritoneum has not been the subject of very great interest. The presence of elastic tissue in the peritoneum was noted in studies of the gastrointestinal tract at the end of the nineteenth and in the beginning of twentieth century (Dobbertin, 1896; Legge, 1897; Livini, 1899; Patzelt, 1936), but the existence of a distinct membranous or reticular structure in the peritoneum of man, analogous to that of the pleura (Spencer, 1977; Thomas, 1987) or of the pericardium (Ferrans, Ishihara & Roberts, 1982; Thomas, 1987), has only been noted by few, and no systematic study of the topographical distribution of the structure has previously been undertaken. In animals, however, the presence of elastic tissue beneath the mesothelium of the peritoneum has been described (Rhodin, 1974) and its presence has been used for experimental purposes (Parsons et al. 1983). While the elastic tissue in the peritoneum of man has been mentioned mainly in the intestinal
serosa (Morson & Dawson, 1979), its alleged presence in the human parietal peritoneum (Seifert, 1927) has only once been convincingly demonstrated (Dobbie et al. 1981; Thomas, 1987). The investigations described in this paper are concerned mainly with the topography of the LEP, because the acceptance of the presence of the structure as a normal anatomical entity is the prerequisite for its use in experimental and clinical work. The LEP is found ubiquitously in the visceral and parietal peritoneum, but developed to a variable extent, according to the properties of the organ it covers. As may be expected, the LEP is most prominent in organs in which a considerable and rapid change of volume takes place, as in the intestines and the gall bladder, while it is less prominent or discernible only with difficulty in static or nearly static organs such as the uterus, appendix, liver, spleen, etc. It is worth noting, however, that at the attachments of peritoneum, the LEP is easily demonstrated. It can, for example, be followed from the parietal peritoneum of the posterior abdominal wall, along the ligaments of the porta hepatis or the spleen until it merges with the copious elastic tissue of their capsules. The stomach is in an intermediate category, being an organ with large variations in size and shape; but as the serosa covering the stomach is scanty, and the elastic tissue of the stomach wall plentiful, the LEP may be hard to demonstrate. As is the case with the liver and the spleen, the peritoneal attachments at the lesser and greater curvatures
45 Peritoneal elastic lamina consistently display an LEP and by following it from there, it may be seen to continue into the serosa of the stomach. In the parietal peritoneum the LEP may be followed from the intestinal serosa along the mesentery to the abdominal wall, as has been illustrated in animals (Rhodin, 1974). It can be found all over the parietal peritoneum, which may have significance for those making peritoneal biopsies. For normal anatomical purposes the LEP is useful, since we can now safely assume that the peritoneum includes LEP. The LEP should also be useful for clinical work. It may provide a baseline for measuring the thickness of the peritoneum in various irritative conditions, for example, in patients undergoing continuous ambulatory peritoneal dialysis (CAPD), or it might give an indication of the extent of metastases within the abdominal cavity. Knowledge of the LEP might be useful for studies of transport of particulate matter across the peritoneum (Parsons, Marko, Braun & Wansor, 1982; Parsons, Marko, Rademacher & Frank, 1985). In relation to nomenclature, it seems preferable for the present to retain the nonspecific term lamina or layer, permitting a more precise term to be devised later. SUMMARY
The structure and extent of the submesothelial elastic tissue of the peritoneum, tentatively termed the peritoneal elastic lamina (lamina elastica peritonei, LEP), was studied in autopsy and biopsy material by light microscopy. The investigation confirms the presence of a well-defined network of elastic fibres just beneath the basement membrane of the visceral and parietal peritoneum in man. The LEP is claimed to be analogous to similar elastic tissue in other serosal cavities, the pleura and the pericardium, as previously described. The LEP may be useful for normal anatomical as well as pathoanatomical investigations. The inspiration and support of my senior colleagues at the Institutes, particularly Dr Peter Stubbe Teglbjaerg, Aalborg Hospital, the technical assistance of Mrs K. Ugilt, Hj0rring Hospital, and the photographic assistance of Mrs A. Dalmose and Mr S. Shapiro, Aarhus Municipal Hospital, are gratefully acknowledged. This study was previously presented in part at the PAX-Conference on Peritoneal Access, Lund, Sweden, in June 1987. REFERENCES
DOBBERTIN, R. (1896). Ober die Verbreitung und Anordnung des elastischen Gewebes in den Schichten des gesamten Darmkanals. Rostock: Universitats-Buchdruckerei von Adler's Erben. DOBBIE, J. W., ZAKI, M. & WILSON, L. (1981). Ultrastructural studies on the peritoneum with special reference to chronic ambulatory peritoneal dialysis. Scottish Medical Journal 26, 213-223. FERRANS, V. J., IsHIHARA, T. & ROBERTS, W. C. (1982). Anatomy of the pericardium. In Pericardial Disease (ed. P. S. Reddy, D. F. Leon & J. A. Shaver), pp. 15-29. New York: Raven Press. LEGGE, F. (1897). Sulla distribuzione topografica dellefibre elastiche nelrapparecchio digerente. Cagliari: Tip. Muscas di P. Valdes. LIVINI, F. (1899). Sulla distribuzione del tessuto elastico in varii organi del corpore umano. Monitore Zoologico Italiano 10, 12-23. MORSON, B. C. & DAWSON, I. M. P. (1979). In Gastrointestinal Pathology, pp. 228 and 492. Oxford: Blackwell. PARSONS, D. F., MARKO, M., BRAUN, S. J. & WANSOR, K. V. (1982). Ascites tumor invasion of mouse peritoneum studied by high-voltage electron microscope stereoscopy. Cancer Research 42, 4574-4583. PARSONS, D. F., MARKO, M., RADERMAcHER, M. & FRANK, J. (1985). Shape changes and polarization of cells migrating through tissue. A high-voltage electron microscope and computer graphics study of serial thick sections. Tissue and Cell 17, 491-510.
46
P. J. T. KNUDSEN
PARSONS, D. F., MARKO, M. & WANSOR, K. (1983). Elastic reticulum and collagen of normal mouse peritoneum. Micron 14, 1-10. PATZELT, V. (1936). Der Darm. In Verdauungsapparat, Handbuch der mikroskopischen Anatomie des Menschen (ed. W. von Mollendorf), Part 3, pp. 292-296. Berlin: Springer. RHODIN, J. A. G. (1974). In Histology; A Text and Atlas, p. 576. London: Oxford University Press. SEIFERT, E. (1927). Peritoneum einschliesslich Netz. In Verdauungsapparat, Handbuch der mikroskopischen Anatomie des Menschen (ed. W. von Mollendorf), Part 1, pp. 337-360. Berlin: Springer. SPENCER, H. (1977). In Pathology of the Lung, p. 77. Oxford: Pergamon Press. THOMAS, N. W. (1987). Embryology and structure of the mesothelium. In Pathology of the Mesothelium (ed. J. S. P. Jones). Berlin, Heidelberg: Springer.
