The cylinder and its layers
Ida's frame for the abdominal wall was never "a muscle" or "a group of muscles." It was a tube — a fascial cylinder with crossed layers, continuous above with the thorax and below with the pelvis. In a 1975 Boulder session Ida laid out the structural problem: the trunk is built as two concentric tubes whose fiber directions run at right angles to each other, and the abdominal region is precisely the zone of the tube that lacks bony spacers to maintain its rigidity. That absence of ribs in the abdomen is what makes the crossed-layer architecture of the abdominals load-bearing in the first place. The orthogonality, in her account, is not decorative — it is the body's substitute for the bony rings the rib cage has and the abdomen lacks.
"That's the only one I can think of right up here. The scaling. Except that the ones back here also. Posterior and medial scaling also come up from They're more vertical than anything. And then these are really the continuations of the tube of the thorax. So the factual plane for instance that lines the inside here, the inside of the inner layer of the tube which is the transversalis fascia in here and the endothoracic fascia in here comes up, I would say, behind the scalenes. The plane that comes up behind the scalenes to the jaw."
Ida's interlocutor in the 1975 Boulder advanced class describes the trunk as a tube with two concentric layers and identifies where the bony spacers run out:
Once the tube is named, the question becomes: how many layers make it, and in what order? Asher, lecturing in August 1974 at the IPR, took the class through the rectus sheath as the cleanest place to see all four sheets at once. The rectus abdominis itself is the vertical muscle running on either side of the linea alba; what wraps it — front and back — is the aponeurotic confluence of every other abdominal layer. The transversus aponeurosis and the transversalis fascia form the deep covering. The internal oblique splits, sending half to the front of the rectus and half to the back. The external oblique covers it all from the front. The whole arrangement converges on the linea alba, where the right and left sides interweave. Reading the rectus sheath from inside to outside is, in effect, reading the entire abdominal wall in cross-section.
"This continues underneath this transversus muscle as the transfer salus fascia. Going all the way around and forming then part of the under side of the rectus sheath."
Asher describes the deep fascial sheet that lines the inner surface of the abdominal wall:
From there Asher builds outward through the remaining aponeuroses. The internal oblique splits to invest the rectus both above and below; the external oblique covers the whole arrangement from the front. Above the umbilicus the dorsal half of the rectus sheath is a fusion of the transversus aponeurosis and part of the internal oblique aponeurosis; the ventral half is the external oblique fused with the remaining half of the internal oblique. All of it ties together at the linea alba — Ida's recurring landmark for understanding how the right side of the body talks to the left.
"The rest of the rectus sheath is formed then by the aponeurosis of the external oblique, the internal oblique and the transversus. What happens at this point if we consider this the rectus abdominis we have the aponeurosis of the transversus with the transversalis fascia coming to form the underside of the rectus sheath."
Asher names the four contributors to the rectus sheath and shows how they laminate above the umbilicus:
Reading the cross-section
In 1976 Asher and Ida brought slides of a cadaver dissection into the Boulder classroom. The most-discussed image was a cross-section through the abdominal wall with the flap reflected back — a single picture that showed, simultaneously, the rectus abdominis in cross-section, the oblique layer external to it, the underside of the rectus sheath, and the visceral fascia on the inside of the cavity. Asher called it his favorite picture. What it allowed him to argue was that the layers are not just stacked but continuous around the corner — the same sheet that lines the rectus from underneath continues medially and laterally to become the lining of the entire abdominal cavity, blending eventually with the iliacus, psoas, quadratus, and obturator fascia. The cross-section was, in effect, the slide that justified Ida's claim that there are not many fascias but one fascia.
"This is a cross section through the abdominal wall with then the flap reflected back. So this is a cross section through the rectus sheath. This is a cross section of the rectus abdominis. This is a cross section through the obliques and we did not find a distinct transversus of this man. So that this then is the underside of the rectus sheath and the fascia continuous which is going to go down and be continuous with the iliacus, psoas, quadratus, obturator internus and so forth. And this then is the fascia which contains a great deal of fat that's related to the intestines. So this is looking into the abdominal cavity. And this is the fascia on the outside. What category of separation did the fascia of the rectus abdominis have with that fascia that is in the intestines?"
Asher introduces the cross-section slide and identifies each layer the section passes through:
Two things in that description repay attention. First, in this particular cadaver Asher could not find a distinct transversus — the muscle was there as part of the oblique mass but had not differentiated as a separate layer. That observation is important because it suggests that the textbook picture of three cleanly separated abdominal sheets is an idealization; what one actually finds on the table varies. Second, Asher named the underside of the rectus sheath as the same fascia that becomes the iliacus, psoas, quadratus, and obturator coverings — the deep abdominal sheet is the front face of the pelvic and posterior compartment structure. That continuity is the bridge the rest of the article will follow.
"And this then is the fascia which contains a great deal of fat that's related to the intestines. So this is looking into the abdominal cavity. And this is the fascia on the outside."
Asher names the visceral side of the cross-section and contrasts it with the muscular fascia:
Confusion in the anatomy books
When the discussion turned in 1975 to which way the abdominal fibers actually run, Ida grew impatient with the textbooks. She had been looking through anatomy books — Lockhart, Cunningham, Woodburne, Hayes — and found their illustrations of the internal and external obliques contradictory. Her hypothesis was unsentimental: the anatomists had never had a well-organized body to dissect, and so the fiber-direction diagrams reflected the distortions of poorly-aged cadavers rather than the true geometry. The position she preferred — and was willing to defend against any single textbook — was that the two oblique layers ought to cross at right angles, completing the orthogonal architecture she had described at the level of the whole tube.
"And I've been looking at anatomy books about the abdominals, internal and external abdominals and there are very confusing pictures in the books as to which way these fibers, muscle fibers go and I'm beginning to think that they're confusing because they've never had a well organized body to dissect. And that perhaps if we had, we would see that indeed there's a right angle heard of structure."
Ida explains why she distrusts the textbook diagrams of oblique fiber direction:
A student in the room pushed back, pointing to a particular diagram that showed the internal oblique fibers turning downward as they approached the inguinal ligament. Ida granted that the diagram existed, but classified it as schematic and functional rather than truly anatomical — and then went further, suggesting that the downward turn in the diagram might be the sag of a poorly-organized abdominal wall translated into anatomical doctrine. If the body were properly organized, she argued, the fiber lines would not turn down toward the pubis; they would maintain their 45-degree relationships all the way to the inguinal ligament.
"And the third thing is And I don't know the meaning of this but as pointed out, the internal oblique as it approaches the inguinal ligament turns down. Yeah, well, that's what I'm talking about. It turns down if you look at most anatomy books and I'm not sure that it ought to turn down. I'm not sure that the turning down is not the sagging of this part of the structure that has brought these lines that are supposed to be like this down."
Ida proposes that what the textbooks show as a downward turn of the internal oblique fibers is in fact the sag of a disorganized abdominal wall:
The third move in this stretch of the 1975 discussion was the more durable one. Ida separated the abdominal wall conceptually into two functional systems — the muscles that go up into the shoulder girdle and the muscles that go down into the pelvis — and located in that division a spiral that crosses the linea alba. The external obliques on one side, she said, are in functional continuity with the internal obliques on the other side, across the midline. The fibers themselves do not cross; the line of force does.
"Second is that there's a way in which that spiral also deepens as it goes down because the external obliques on one side go through the linea alvia and down into the internal obliques, that line of force crosses the midline. The line of force, not the fibers themselves."
Ida names the crossed-spiral logic of the obliques: external on one side, internal on the other, linked through the linea alba:
The linea alba as crossroads
Everything in the abdominal wall converges on the linea alba — the midline tendinous seam where the aponeuroses of all three flat muscles, plus their counterparts from the opposite side, interweave. In Ida's reading, the linea alba was not merely a connective-tissue stripe down the middle of the belly; it was a structural junction where the right-side spiral met the left-side spiral and crossed. If the abdominal wall is a crossed system rather than a paired system, then the linea alba is the place where the crossing physically happens. Practitioners attentive to abdominal work end up reading the linea alba less as a line and more as a knot.
Asher's cadaver work brought the linea alba into still more concrete focus. The transverse inscriptions of the rectus abdominis — the tendinous bands that visibly segment the muscle in well-developed bodies — were, in the 1976 specimen, distorted and irregular at exactly the points where the body had pulled them out of true. At each inscription the fascial sheath was, in his memorable word, glued down: the practitioners could not tease the layer free with their fingers, only cut. That observation gave Ida's geometric argument a concrete pathology: the linea alba and the inscriptions are precisely the places where disorganized abdominal walls become structurally adhered.
"I mean it doesn't just form a sheet around the muscle, it embeds, goes around it and mixes in with it and, you can see some of that here, the connections on the underside. You see how these so called inscriptions which came from the original segmentation, it's like this is the umbilicus right here. That's nice and straight but here because of all the pulls that we've had in the various way of holding the body, these have become quite distorted and irregular. Costal Arch is right about here. And also these inscriptions were literally glued down or at the point of these inscriptions, the fascial sheath in this man was literally glued down. We had to cut this. This was not a matter of teasing. This was really glued down."
Asher describes the rectus sheath dissection and the gluing-down of the inscriptions:
The same dissection produced one more relevant observation: the external oblique fascia at the costal arch and umbilicus carried, in this cadaver, the full record of the man's habitual abdominal pull. The fascia on the surface of the rectus was discontinuous in its tension from the fatty superficial fascia outside it; both, in turn, were continuous with the heavy sheets in the groin that maintained whatever shortness the body had habituated. Ida's broader point — that fascia organizes the body and records its history — found in the abdominal wall one of its clearest demonstrations.
The deep sheet continues inward
If the rectus sheath is read from the inside outward, the innermost layer is the transversalis fascia — the deep lining of the abdominal cavity. In the August 1974 IPR lecture Asher devoted a long stretch to following that fascia inward, around the corner of the pelvic brim, and into the deep posterior compartment that houses the psoas, quadratus lumborum, and iliacus. The aponeurosis of the transversus extends laterally and posteriorly until it reaches the lateral edge of the quadratus; the same sheet then sends a septum forward to invest the psoas. The deep abdominal wall, in other words, is the front face of the same compartment system that, viewed from the back, is the lumbar dorsal fascia and its extensions.
"Now this, there's an extension from this fascia then going out to form really the aponeurosis of the transversus muscle, the transversus abdominal muscle."
Asher names the continuity between the deep posterior fascia and the transversus aponeurosis:
The implication for the work is concrete. When the practitioner addresses the iliac crest from above, the layer being changed is most directly the transversalis fascia — the deep lining of the abdominal wall — because the transversus aponeurosis attaches there. When the practitioner reaches the psoas from the front, the sheet being engaged is the iliac fascia, which is continuous with the same transversalis layer. Asher's argument is that the abdominal wall and the deep pelvic-posterior compartment are not adjacent regions but two faces of one cylinder, and the practitioner working at the crest is always, whether intentionally or not, affecting both.
"Starting up here then, we would have the whole internal lining of iliac bone aligned by the iliac fascia which is of course going over the iliacus and also covering the psoas. This is going to be continuous with the transversalis fascia of the transversus muscle up in the abdominal region. It will also, as I indicated in the brief talk last time, be continuous with that fascia of the quadratus lumborum. It will be continuous below and posterior with the fascia of the piriformis, which is coming from the sacrum. It will be continuous with the fascia of the iliacus, the obturator fascia. And then by the attachment of the combination of the tendon of the iliacus and the psoas, of the iliopsoas tendon be continuous with the fasciata. And also probably, yeah, would be from the side continuous with the fascia of the pectineus. So actually, we may never, Tom did to me the other day, but frequently in the first ten hours we don't get to the iliac fascia."
A week after the August 5 lecture, Asher returns to the same continuity and traces it through the pelvic floor:
Asher and a student worked through the same continuity from a different angle in 1975. The transversalis comes around the corner of the ilium and opens out, the student offered, to include the psoas; then there is another sheet, and the quadratus. Asher confirmed: the compartment has two sub-compartments inside it, one for the psoas and one for the quadratus. The sheet they share is the deep continuation of the transversus aponeurosis — the same sheet that, viewed from in front, is the deep underside of the rectus.
"I I what I got when you said it was that this this transversalis fascia comes around the corner of the ileum, and then it and then it sort of opens up to include The psoas. The psoas, and then there's another sheet, and then there's the quadratus, and then there's a sheet Mhmm. Which are kind of which come out of the same primary Yeah. Sheet as it comes around the corner. And that that is sort of a compartment Mhmm. Which has two compartments within it, one for the psoas and one for the quadratus. Is that That's what I'm getting."
A student in the 1975 Boulder class works out the compartmentalization of the deep posterior layer with Asher:
The deep sheet at the back
Read from the back rather than the front, the same compartmental geometry is the lumbar dorsal fascia and its derivatives. In the August 1974 IPR lecture, Asher walked the class through the dorsal anatomy at roughly L3 — the cleanest level for inspection — and showed how the lumbar dorsal fascia wraps the erector spinae, reflects forward between the erector and the quadratus to attach to the transverse processes, and then sends another septum forward between the quadratus and the psoas. The result is a continuous sheath that links three muscles — erector, quadratus, psoas — by a single layered fascial system. The abdominal wall is the front of this same cylinder.
"Now, we have then the covering, the lomo dorsal fascia covering the erector spinae with of course a superficial fatty fascia over it. I'm just talking now about the deep fascia of the lumbar dorsal fascia. This then at the point of junction between the erector spinae and the quadratus lumborum reflects back between those two muscles to attach to the transverse process. This then is referred to as the dorsal, I'm not exactly sure but I think it's called the dorsal ligament or the dorsal extension of the lumbodorsal fascia in the lumbar region. It also, it's in a sense a split here so it is sending out also a covering or else fusing with the covering of the quadratus lumborum on its dorsal surface. The other was ventral surface."
Asher describes the lumbar dorsal fascia's reflection at the lateral edge of the erector spinae and its passage forward to the transverse processes:
Asher returned to the same arrangement in 1975, citing a researcher whose dissections suggested that the quadratus and the erector spinae actually lie in two separate sheets — not the single compartment most anatomy books describe. The revised geometry is more useful for the practitioner, because it places the quadratus and the psoas together in front of the erectors, with the erectors in their own posterior pocket. That arrangement is exactly what allows the practitioner working on the iliac crest to address the deep abdominal layer and the lumbar layer in the same gesture.
"specimens, they have to really do a fancy dissection. We're right at the at the lateral edge of the quadratus lumborum because the backside of the quadratus butts onto the erectors. That's what all the anatomy books say. He doesn't say that. He thinks it's a separate that there's two separate sheets. That's more sensible because that puts the quadratus and the psoas in the same compartment and the and the erector's posterior. Well, I don't think it puts the psoas in the same compartment. Splits It the side layer. It it splits and closes psoas, but then the psoas has its own fascia covering within that covering. What did he say? And he also said he's done very fancy dissection to prove that."
Asher reports a researcher whose detailed dissection separates the quadratus and erector compartments:
Superficial and deep on the abdominal surface
Above the deep sheet sits the muscular layer; above that, the deep fascia of the muscles themselves; above that, a thick fatty superficial fascia; and above that, the dermis and skin. In a 1976 cross-section taken from the back, Asher walked the class through each of those layers in dissection sequence and made a methodological point: the layers are quite thin — each is a matter of perhaps a millimeter — and the term "superficial fascia" comprises everything from the underside of the dermis down to the surface of the deep fascia investing the muscle. The classical scheme that distinguishes superficial fascia, deep fascia, and visceral fascia is the scheme Ida and Asher worked with.
"Well I thought maybe that was shown on the slides of the As I said, was very sleepy at 07:00 this morning and at least isn't upside down even if it is backwards. But this was a, actually this was Jim Asher's creation of getting the concept of the layers of fascia down starting with the external skin. This was a 43 year old male of the cadaver. This was the external skin I think were taken somewhere in the back, somewhere up in here, in the latissimus dorsi region. So that we have then the skin here then immediately what we did was to peel just the skin back. This is leaving probably partly dermis. This is the same thing here, these two. And so that this is the kind of tissue which you see is, it has some fat in it but it's a very tough tissue in terms of texture. It is not a giving easy tissue to work with. Then we sort of artificially went down another layer so this is what we saw still in just the layer below that. Now these are a matter of probably a millimeter that we're taking. It's a very thin area. Then we took this off so we go down to this region. Now this is all what we call superficial fascia according to the classical definition. And then we're down to the fascia that is immediately over the muscle itself which we call the deep fascia or I started to call the deep, the superficial deep fascia which is something we have to do about terms. So it's really in a sense a cross section of the skin, the kinds of things that we're working through. Now these few slides are mainly to give you an idea of different kinds of fascia and that we have layers of fascia or fascia sheaths which I feel are due to the concept is the tough sheaths are due to improper use of the body."
Asher walks the class through the layered dissection sequence of skin, superficial fascia, and deep fascia:
Two claims in that passage are worth pausing over. First, Asher introduced a vocabulary the rest of the field has not always kept: he was inclined to call the deepest part of the superficial fascia "the superficial deep fascia," because the conceptual line between superficial and deep is not as crisp as the textbook diagrams suggest. Second, and more important for Ida's teaching, he said that the tough sheets one finds between muscle layers in most dissections are due to improper use of the body, and that what the practitioner is working toward is a soft bed of connective tissue rather than these toughened sheets. This is the doctrine that gives the abdominal work its target — the fascial layers should be present but supple, distinguishable but not glued.
"It's thick, very loose, and there's an inner layer that's like a membrane. Those two are connected pretty strongly. Okay, the outer layer's adipose tissue contributes to body contour, provides insulation and storage of nutrients. The inner layers are thin membrane, large amount of elastic tissue. So the superficial fascia can slide over the deep fascia. Okay, now you got the shopping bag.
Ida and a student describe the superficial fascia as a flexible bag with a fatty outer layer and a thin elastic inner membrane:
Gluing-down at the back: the gut and the spine
Asher's 1976 cross-section showed one more thing the class did not always anticipate: the major attachment of the deep abdominal fascia to the viscera is at the back, not the front. The fascia on the inner side of the rectus could be separated from the visceral fat with relative ease — it was loose, though it had to be teased apart — but the large intestine, on the back wall of the cavity, was literally glued down to the posterior fascia. Asher's developmental explanation was that the gut originally develops from the back; the posterior wall is its original anchor; and what looks in the adult like over-attachment is the residue of that developmental anchoring, frozen in place by years of disorganized loading.
"What category of separation did the fascia of the rectus abdominis have with that fascia that is in the intestines? Did you just lift it off or did you have to separate it? We had to do some separation, it was very loose, but we had to do some separation. The main tie up with the fascia here is on the back. Now if you remember that the gut and everything develops from the back, that makes more sense because that was the original tightness or toughness or support, was back here. So then a lot of the lack of connection here I feel is an over connection back here. It's like the large intestine was really glued down to the fascia on the back. Very tight. That's part of the development pattern. I think so, yes. They used to hang like this."
Asher describes how the major fascial connection to the viscera in this cadaver was at the posterior wall, not the abdominal front:
This is the move that completes the topic. The practitioner working on the abdominal wall is not, in Ida's framing, working on a single front-of-body structure. The crossed-fiber architecture of the obliques, the rectus sheath, the linea alba — all of that is the front face. But the back of the same cylinder is the lumbar fascia, the quadratus, the psoas, and the posterior anchoring of the gut to the spine. Asher named this explicitly: when the practitioner loosens the erectors, the quadratus, and the psoas, what is also loosening is the attachment of the gut to the back. The abdominal wall is not the front of the body. It is the whole circumference of the trunk's deep cylinder.
"part of the development pattern. I think so, yes. They used to hang like this. Well sure and you see as the gut develops it does hang at first until the body grows around it. Well I wonder about that because you And of course it's the right back here that's necessary to allow that and if we think then that we're not only loosening erectors, quadratus and psoas but we're also loosening the attachment of the gut in the back here."
Asher names the practical consequence: working on the erectors, quadratus, and psoas is also working on the posterior attachment of the gut:
Coda: the layers as one fascia
What emerges across these passages is not a catalogue of separate sheets but a single layered cylinder. From the skin inward: dermis, superficial fascia (fatty outer plus elastic inner membrane), deep fascia of the muscle layer, the three muscle layers themselves with their aponeurotic continuations into the rectus sheath, the transversalis fascia lining the cavity, and the visceral fascia on the intestines. The fiber directions of the three muscle layers cross at right angles where the body is well-organized; the aponeuroses converge at the linea alba; the deepest sheet continues without interruption into the psoas, quadratus, iliacus, obturator, and pelvic floor.
Ida's structural argument across the topic is that what the textbooks present as separate fascias are aspects of one fascia — the connective-tissue organization of the trunk's cylinder — and that the apparent multiplicity of named layers is partly an artifact of dissection and partly a pathology of population structure. The abdominal wall is the place where this argument is easiest to make, because the cross-section through it shows in one image the full layered architecture of a body. Asher's slides made the argument visible; Ida's framing made the argument structural. Both belonged to the same project.
"Okay, now you got the shopping bag. Right? Flexible bag. And in that bag, we're going across 42nd Street. 34th Street. 34th. 35th. And 7th Avenue. Okay. Now in that bag, you got a bunch of stuff. Let's put some brains in there, a heart, some bones. Throw in some glue. Okay? Now here's the key point. This is the bag with all this stuff in it, just like the body. What are you gonna do to organize that stuff? How are you gonna do it? Well, the fascial planes are the organizational material for the body. It's what I think. K. And if you look at it from an evolution standpoint, there's some massive protoplasm there. As that protoplasm gets more organized, in other words, higher structures come to be like a nervous system, the nervous system gets more organized. In other words, instead of a bunch of cells just floating around into this large massive protoplasm, the connective tissue organizes that into a system. Okay?"
Ida closes with the bag-of-stuff image and the claim that fascial planes are the body's organizational material:
See also: See also: Boulder 1975 (B4T3SB) — the long opening discussion in which Ida traces the visceral fascias from the pre-tracheal layer through the pericardium and peritoneum to the transversalis fascia, establishing the three-layer scheme (somatic / deep / visceral) within which the abdominal wall layers sit. B4T3SB ▸
See also: See also: Boulder 1975 (B3T8SB) — Asher's working definition of a fascial plane as distinct from the investing fascia of an individual muscle; useful background for understanding why he distinguishes the aponeuroses of the obliques (which form planes) from the deep fascia of the muscles themselves. B3T8SB ▸
See also: See also: IPR Lecture, Aug 5, 1974 (74_8-05A, chunk 12) — Asher's extended treatment of the lumbar dorsal fascia and the latissimus dorsi aponeurosis, which forms the dorsal continuation of the abdominal cylinder. 74_8-05A ▸