In the male adult the abdomen presents an .expanded convex surface anteriorly (the ante rior wall or proper abdominal region) ; poste riorly a broad surface not so extensive, situated between the last ribs and the superior margin of the pelvis, and divided into two by the lumbar portion of the spine (the posterior wall, the loins, or lumbar regions.) The anterior and posterior walls are connected with each other on the sides by two narrow regions (the lateral walls or the flanks.) • The outline of the anterior wall or pro per abdominal region constitutes an oval, whose long axis is vertical. The surface is generally more or less convex during life, proportionally with the degree of embonpoint of the indivi dual, and also according to the condition of the diaphragm. After death, excepting in very fat subjects, or where the intestines or peritoneal cavity are much distended from any cause, this surface is in a variable degree collapsed, and more or less concave, but especially so in very thin and emaciated subjects. There is a con stant adaptation in the condition of this surface to that of the abdominal viscera, so that the practitioner can in general argue pretty accu rately, from the state of the abdominal surface, respecting that of the abdominal viscera, ex cept in cases where every thing is masked by a superabundant deposition of adipose substance. So close is the apposition of the abdominal wall to the surfaces of the subjacent viscera, that in some cases of extreme emaciation the peristaltic movement of the intestinal canal is manifested by the successive elevation and depression of small portions of the walls corresponding to the dilated and contracted portions of intestine. This surface is divided into two equal and symmetrical portions by a groove which exists along the middle line, and which is chiefly ap parent in the two superior thirds. This groove commences below the ensiform cartilage, where there is a slight depression, denominated the scrobiculus cordis, (creux de l'estomac.) In this line, about midway between the pubis and xiphoid cartilage, is the round depression called the umbilicus or navel. Just over the pubis there is a prominent surface in both sexes covered with hair ; in the female it is much more pro minent than in the male, and is called the mons Veneris. In subjects the muscular sys tem is well developed, there exists on each side of this median groove an oblong convexity, ex tending from the anterior surface of the lower part of the chest to the pubis ; these convexities indicate the situation of the recti muscles. In statues representing athletic men, the promi nences occasioned by these muscles are gene rally very well shewn, and are divided by trans verse superficial depressions into smaller qua drilateral portions, generally three in number. External to these prominences there is, in similar muscular subjects, a fissure extending from the border of the chest, in a slightly curved course with external convexity, to a point a little to the inner side of the anterior superior spine of the ilium ; this fissure has internal to it the prominence from the recti muscles, and external that from the broad muscles of the abdomen. Gerdy calls it the lateral groove or furrow of the abdomen.* (See fig. 1.) The posterior wall or the region of the loins, ( lumbar region,) is in every way of less extent than the anterior. Its vertical height is equal to the distance between the last rib and the margin of the ilium. It is continuous on the sides with the flanks, and is divided along the middle line by a groove, corresponding to the lumbar spinous processes, into two symmetrical portions, each of which forms a large and pro minent relief. Each relief corresponds to a great muscular mass, which almost wholly oc cupies this region, and its prominence is greatest when those muscles are in a state of contrac tion, as during the erect posture. Each relief is coneave from above downwards, and in a degree directly proportionate to the contrac Lion of the muscles, insomuch that in some in dividuals the concavity is habitually very con siderable, as in those who carry burdens on the head or in front of the body, in pregnant wo men, &c. (See fig. 2.) The limit of this wall on each side is indicated by a groove or fissure which passes obliquely upwards and outwards towards the ribs, and corresponds to the outer margin of each relief, or that of the lumbar muscles ; these lines also indicate the posterior limits of the lateral walls of the abdomen, or the flanks. Anteriorly the flank of each side is continuous with the anterior wall of the abdo men ; above it is limited by the margin of the thorax, and below by the margin or crest of the ilium. It is concave on its surface abcve downwards, (except in cases of great embon point, where the concavity is obliterated,)' and convex from before backwards. Gerdy remarks that in subjects in which the muscles, have a considerable development, a relief is formed just above the crista ilii by the broad muscles of the abdomen at their insertion into this osseous border. Upon antique statues this
relief is in general made too prominent.
The anterior or proper abdominal region has been subdivided into smaller compartments, with a view to facilitating descriptions, patho logical or otherwise. This subdivision is com pletely arbitrary, and therefore some differences will be found among the various anatomical authors as to the precise limits of each region. That which is here subjoined, however, appears to be pretty generally agreed upon in this country. Lines connecting particular points drawn upon the surface, mark out these subdi visions, and if planes be supposed to be carried from these lines horizontally backwards to the posterior wall, the cavity of the' abdomen will thus be divided into segments, each of which has its particular portion of the abdominal viscera. It is an instructive exercise for the student to practise himself in examining the particular viscera which correspond to particu lar regions. We are thus enabled, as Blandin has remarked, to resolve the problem, " a point of the surface of the abdomen being wounded deeply in a given direction, to de termine what organs have been injured ; and reciprocally, an organ having been wounded in a particular part of the abdominal cavity by a sharp instrument, which entered in a given direction, to determine what part of the abdominal walls must necessarily have been injured."t The limits of these several regions or com partments may be thus indicated : I let a line be drawn horizontally from the extremity of the last rib on one side to the same point on the other, and let another line parallel to the pre ceding be drawn between the two anterior superior spinous processes of the ilium ; the abdominal surface is thus divided into three great regions, each of which is subdivided into three by means of a vertical line let fall on each side from the anterior extremity of the seventh or eighth rib to a point a little external to the spine of the pubis Nine regions are thus marked out, the relations and boundaries of which may be described as follows.
The superior region, or that above the first horizontal line, is the Epigastrium, which name it derives from its close relation to the stomach : (E9r&, upon, over; vacrTne, the stomach.) The epi gastrium is bounded superiorly and laterally by the margin of the thorax, and its inferior limit is indicated by the transverse line. The verti cal lines subdivide it into two lateral regions, each of which is bounded immediately above by the lower margin of the thorax, beneath which these regions extend in a direction up wards and backwards : they are hence called hypochondria (veto, under, zoykoc., cartilage). Between the is the proper epigastric region, which at its superior part and just below the xiphoid cartilage presents the depression already alluded to under the name of scrobiculus cordis (scrobiculus, the diminutive of scrobs, a depression).
Immediately below the epigastrium, and separated from it by the superior horizontal line, is the umbilical region, which has its name from the presence of the umbilicus in it. This region is limited and below by the two horizontal lines, and is subdivided by the intersection of the two vertical lines into three regions : the lateral ones are the lumbar regions, so called from their correspondence with those portions of the posterior abdominal wall which bear the same name ; and the middle one is the proper umbilical region. .
Between the inferior horizontal line and the margin of the pelvis, is the hypogastrium,(vro, beneath, vcarrng, the stomach). This region is li mited below in the centre by the pubis, and on each side it communicates with the upper part of the thigh. It is subdivided into the iliac regions on each side, and the proper hypo gastric or pubic region in the centre. The two former constitute the upper or abdominal portion of the great region of the groin, which is completed inferiorly by the upper part of the anterior of the thigh. These regions afford peculiar interest to the surgical ana tomist, in consequence of the occurrence in them of the most common forms of hernia.* (See GROIN, REGION OF THE.) The structures which enter into the com position of the abdominal parietes, or their elements, (as the term has been lately applied,) are-1. the skin : 2. the subcutaneous tissue or superficial fascia : 3. muscles and their aponeurotic expansions : 4. a particular fibrous expansion, or fascia : 5. a thin and filamen tous cellular tissue, which separates the fascia just named from the sixth element: 6. the peri toneum, which, however, is not to be found in the composition of all the walls of the abdomen.