A Meditation on Scoliosis

by Erik Bendix

            It is evident that people are vertebrates.  Our core of segmented bones following the lead of the head is a structure we share with all mammals, birds, reptiles, amphibians, and fish.  Of these, the fish are our most ancient brethren.  A quick comparison of a human skeleton with that of a fish shows that our limbs are more recent additions to the old design.  It is interesting that our limbs add onto the spine in the way that they do, symmetrically on either side of it, rather than, say, only on one side, or out the front or back.  We are symmetrical side to side, and it is worth asking why.

            The symmetries we see in ourselves and in our vertebral kin are not just what can be seen on the surface.  The inner structure of the human nervous system, for example, is bilaterally symmetric to a fault.  The cerebral cortex divides into equal right and left halves, so do the cerebellum and smaller subcortical structures, and so does the spinal cord itself, which has little central grooves front and back called median fissures which divide it neatly into lateral halves.  Why are we built this way?

            These symmetries must have developed in response to some need.  Since all vertebrates share this symmetry of form, the needs that gave rise to it must have existed right from the beginning of vertebral life.  Fishes were the pioneers among vertebrates.  Prior to them, creatures in our yet more ancient line of ancestry could propel themselves at best very slowly and without much aim.  Fish changed this into targeted and self-propelled pursuits of food.  They began to hunt.  Their ability to travel in this way gave them their crucial edge in vying with other life forms.  A spine and muscle system capable of propulsion and a central nervous system capable of navigating had developed together to make such locomotion possible.  It is these anatomical systems that most markedly display bilateral symmetry.

            Anyone looking at swimming fishes can see that they propel themselves by bending from side to side.  It is reasonable to suppose that something like this movement was how the very first vertebrates got around.  It is also worth asking whether such movement might have anything to do with the basic side-to-side symmetry we still display through most of our anatomy.  Could our bilateral symmetry of build in some way be a result of the first and most basic needs of vertebrate movement?

            To answer such a question, and to understand such a naturally evolved movement, it is worth considering the energy expended to bring the movement about.  The harnessing and use of energy by organisms is one of life’s most precious accomplishments, and nature is not prone to waste it.  This is why natural movement so often seems beautiful to us, for its elegance lies in its superb efficiency.  So to understand the wriggling of fish, we must look to what makes such movement efficient, or not wasteful of energy.  The fact that fish do their moving inside of water cannot alone account for their mode of propulsion, for water surrounds them equally on all sides.  In principle at least, water affects all types of movement within it equally.  Whatever it is that could make one kind of fish movement more efficient than another must itself have a bias in some direction.  The most obvious candidate for such a bias is gravity, perhaps as it is expressed in how water becomes denser as it deepens.

            If a fish moves at all times parallel to the ocean floor, never thrashing up and down, but only side to side, its movement remains neutral in relation to water density and hence to earth’s gravity.  No part of such movement has to fight against water density more than any other, and so the effort of such movement is evenly distributed and thereby minimized.  Because side-to-side movement stays within one range of water density, it is also much simpler for the fish to control.  Continual up and down movement would have required a nervous system capable of constant compensation for density differentials in the water.  This too would be an unnecessary use of energy as long as simpler solutions were available.  So the elegance of fish in motion and their relative simplicity of locomotory intelligence are both gains from the standpoint of saving energy.

            It is a short step from here to an understanding of why the side-to-side movement of fish required a structure that was symmetrical on either side of the spine.  Fish moved because they were in pursuit of prey. Bilateral symmetry is the simplest possible structure for ensuring that bending to either side balances out to a well-aimed mouthward journey toward dinner. Had fish been laterally asymmetric, they would have been foiled in this attempt, and would have swum in circles: the creatures that lacked symmetry must have died out before reaching their meals!  This evolutionary selection has stayed with us ever since:  our limbs, our eyes and ears, our muscles and nerves and bones are all genetically predisposed to pair up equally side to side.

            Does such symmetry run all the way through us?  Indeed not.  The biggest exception in our anatomy must be in our digestive system.  The human stomach loops to one side, the liver to the other, the pancreas sits on an odd diagonal from back left to center front, joining its duct to that of a gallbladder tucked under the liver on the other side of midline, and both emptying into a veritable chaos of intestinal tubing.  Where does such a crazy arrangement come from, and why is it so different from our skeleton, muscles, and nerves, which divide us so neatly and equally into right and left halves?

            Ancestry can again be our clue.  The experiments performed by nature to develop a gut method of digesting came before the development of a spine among the fishes.  Being as yet unconstrained by the needs of locomotion, the gut had no need to become streamlined around a central axis.  Indeed, the getting of an axis to begin with may have required differentiating the feeding end of an organism from its waste end.  The process of gut development was one of getting the food to move in one direction through the system, so that digestion could become specialized into stages that would make its chemical process more efficient.  During this prevertebrate evolution, an exceedingly diverse variety of forms were tried, from all manner of worms and filter feeders to sea urchins and starfish, nothing like the basic uniformity of structural blueprint among the vertebrates.  Perhaps this chaos of forms still echoes in our gut, and our bilaterally symmetric bodies have evolved, as it were, around them, reluctant to discard a design that works and that took aeons to secure.

            The creatures that first had food go in one end and out the other acquired their basic directionality by this arrangement.  Which way they were oriented relative to dinner was no longer a matter of indifference.  It was the mouth end that needed to aim and eventually to locomote in the direction of food.  The head, with its ability to notice and reckon, then evolved later to serve the needs of the mouth in getting to food.  The result was directional movement:  life became a journey. 

            This was an enormous change, and it came at a cost:  the loss of directional indifference seems to have sharply curtailed the ability of organisms to regenerate lost parts.  It was as if acquiring the ability to aim and move made life less reversible.  Starfish can regrow lost arms; vertebrates generally cannot.  They make up for this loss by their ability to flee and pursue.

            There are other reasons to think that the beginnings of locomotion, for all the glory they gave us vertebrates, may have been less than ideal.  It is possible that the arrangement of a symmetric sheath of vertebral skeleton and muscle and nerve tissue surrounding an asymmetric core of vital organs didn’t and doesn’t always work exactly right.  The way in which the two systems attach to each other could create problems if the need for symmetric movement of the sheath were not always met with an even resistance from within.  Organs are suspended and held in place within skeletons by means of sheets of fascial tissue, and it is quite possible for the slack or tautness of such tissue to be uneven, especially if some organs require slack for their continual expansion and contraction, while others need only hold their place.

            Just such a situation is most evident just below a person’s ribs:  on the right side sits the huge and relatively unperturbed liver, while one the left the heart beats in and out constantly while the stomach swells and shrinks most drastically of all organs with its daily feast and famine.  Clearly the left side must have more slack or elasticity to accommodate movement than the right.  From this, one would expect the thoracic spine behind these organs to be more tightly tethered to the liver side, and more apt to yield toward and away from the stomach.  Similar considerations would lead one to expect the spine higher up to have some leftward slack in how it tethers to the heart.  The lungs and intestines also have asymmetries that must be accommodated.

            From these speculations about how elastic the tethering of organs to spine might be, one might expect the human spine to have some tendency to list toward the side with less internal movement among the organs.  This seems to be born out by statistics on human scoliosis.  The most common lateral curvature in human spines is in the thoracic region, and of these, 90 per cent curve to the right when viewed from behind.  The statistics usually separate curves in different regions of the spine.  Thus thoracic curves within the rib-connected spine are looked at separately from curves that span into the lumbar region, and again from curves that fall entirely within the lumbar spine.  “Double major” curves that go one way in the thoracic spine and the other way in the lumbar are also treated as a separate category.  But if we are concerned with organ fascia in relation to the spine, we must look at the entire spine in relation to all the organs to get the comparisons needed.  Putting the various statistical categories together gives an even clearer picture of the vast majority of human scolioses showing convexity to the right up above and convexity to the left below when viewed from behind – various versions of the shape of a question mark traced out on a person’s back.  Most such cases are seen as genuine question marks by current medical opinion:  they are seen as idiopathic, which means their causes are unknown.  Curves that deviate significantly from this basic pattern usually do have causes that can be identified, but they constitute less than a tenth of the total.

Even if lateral pulls due to asymmetric organ tethering occur mainly in the middle just below the diaphragm, there are other more major forces at work that form a context around such deviations:  gravity and the attempt to stand upright will make everyone at least try to get their feet under them and their heads raised, even if the whole spine isn’t willing to straighten in response.  Left convexity in the lumbar region or even in the upper thorax or neck could just be compensations for trouble in between. It is possible that the need to accommodate the asymmetrical needs of the organs could be at the root of many of the lateral curves seen in scoliosis.

            All of this begs the question why we aren’t all scoliotic, since we all have stomachs and livers.  This would seem to be an absurd conclusion, but it may not be as far-fetched as it appears.  For one thing, the relative size and shape and even position of people’s organs have a wide range within which they are still normal, and it is reasonable to expect the fascial tissue around them and its relative tautness to differ as well.  For another, medical science is chiefly concerned with scoliotic curves that pass a certain degree of severity and that thus become gravitationally unstable and prone to deterioration.  These are the cases most likely to require medical intervention.  Of less concern to medicine are curves that are stable, and especially those that are slight enough to evade notice.  It is possible that most of us have some degree of such curvature.  Besides, the spine is a somewhat flexible column, and most of its curves change continually during normal movement.  At least some lateral bending can normally be induced at will.  It would be interesting to know how far the lack of such flexibility correlates with scoliosis.

            Severe worsening of scoliotic curves tends to afflict adolescent girls more than boys, and among girls it is the ones who grow faster sooner who are more at risk. Why is this?  If it were just hormonal, why aren’t the later growers equally affected?  Might it be nutritional?  Are these girls getting enough to eat just when they need it most, in the years of their growth spurts?  Is it their empty stomachs that are pulling them out of line?  Do they perhaps not see the point of nourishing themselves well?  The image-making industries that cater to them probably care even less about their health than they do.  Our social values do seem to reward the outward appearance of symmetry, and to neglect the lopsided inner core that sustains and nourishes us.  The money we lavish on athletes, models, and movie stars certainly dwarfs what we are willing to pay cooks, farmers, and mothers.  In a social environment that heaps such reward on the beauty of outward symmetry and pays such scant heed to developing an inner life, scoliosis may look more akin to other failures of nourishment such as anorexia and bulimia that shadow those who devote their lives to how they look.

            In the case of scoliosis, the medical approach has been to try to prevent its worst consequences, either through externally bracing the most unstable curves or through surgery.  There is probably enough of this sort of work to keep the specialists busy.  The question for the rest of us is whether the problem is thereby dealt with. There must be ways to prevent the worsening of scoliosis, perhaps to head off its inception or reverse it, and these ways may lie beyond the scope of specialized medicine.

            An obvious first line of defense against scoliosis, as against many disorders, is simply that of eating and breathing well.  If scoliosis is indeed a matter of interaction between organs and spine, caring well for the organs is as necessary for prevention as for any possible cure.  The kind of interaction between organs and spine discussed earlier was not just one of nutritional support.  It was specifically also one of an interaction of movements between asymmetric organs and the symmetrical musculoskeletal sheath surrounding them.  Medicine braces severe scoliosis against movement that could make things worse.  But is there movement that could make things better?  The spine, after all, is a flexible column, and lateral flexion is normally not a postural set, but just a possible way to move.  So another way to pose our question is to ask if scoliotic posture is in some way a freezing of movement that could be thawed in such a way as to move toward a resolution into full uprightness.

            If this is even a possibility, it would be good to clarify again what is involved in vertebral movement.  We humans inherit a very long line of vertebral evolution.  By the time that spinal inheritance reached us, it had gotten quite complex.  While fish may have relatively identical vertebrae that they carry at rest in a simple straight row, our spines have evolved fairly permanent curves and specializations of bone structure in response to our being on land and being upright. 

            We may recall that for a fish to move in a straight line through the water, rather than in a circle, its flexion to one side must balance its flexion to the other side.  The simplest way to achieve this is for it to be structurally symmetrical side to side; other things being equal, we can assume that nature would select toward this solution.  Now a fish that has been caught or beached will thrash around in full flexion from one side to the other as it fights for its life.  The more differentiated waves of flexory movement that pass down a fish’s spine in normal swimming are a response to a safer environment.  Full lateral flexion is thus most likely an earlier more primitive reflex, while waves of flexion require more subtlety of control and may have built on modulating that initial simpler response.

            The fish is a segmented creature, not just by its string of vertebrae, but by the nerves and muscles associated with each segment.  In the simple case of thrashing side to side, all the nerves and muscles on one side are activated together, followed by all the ones on the other side.  Modulating such action to produce the waves we recognize as fish swimming requires different segments to alternate “turning on and off”, so that the sequence of contractions move down the line of segments toward the tail in a wave, balanced by an equal wave of releases of contractions moving down the opposite side at the same time.  The waves of movement travel tailward, and as they do they push against water resistance which thrusts the fish headward. 

            This basic organization of motor impulses traveling tailward, while water resistance propels the organism headward is basic to vertebral life, and underlies much later complexity.  From the neural standpoint, it is an efficient and simple system, since the direction of sequencing corresponds to the direction from which the impulses originate in the brain and travel tailward through the vertebrae.  From the standpoint of mechanics, the differentiated waves of lateral bending form a shallower angle to the spine than full lateral flexion would have done.  This makes their thrust against water resistance go much more directly tailward.  Less energy gets wasted out to the sides, where it would have created more drag against the direction of travel.

            As we have described the locomotion of fish, there is still an even ratio between muscles that engage and those that release.  For every contracting muscle on one side there is a releasing muscle on the other.  To improve efficiency beyond this point, the ratio between contraction and release would have to begin to tip toward a higher proportion of release.  The corresponding ratio between excitation and inhibition of nerve messages to the muscles would also have to begin to shift toward inhibition.   If a smaller proportion of the musculature could bring about the same propulsion, efficiency would thereby be gained.  In more graphic terms, an animal that moved more quietly would have an advantage.

            Something like this seems to have actually happened in evolution among predatory fish in the shallow seas of the Devonian Era, some 360 million years ago.  These fish evolved limbs as a way of sneaking more quietly through the water to stalk their prey.  This change in turn laid the foundation for vertebrate animals to come out of the water and onto land.  To understand this change, one must understand how fish sense movement underwater.  The way fishes usually move sets up waves of disturbance in the water to either side of them.  Fish are well equipped to sense such disturbances by means of sensory organs they have that are called lateral lines.  The next time you see a whole cooked fish lying on its side on a restaurant platter, you might notice that its meat on each side divides into top and bottom halves.  The groove that divides them contained a lateral line sense organ in the living fish.  Fish use this organ to detect changes in water flow past their snouts and sides.

            For a predator, this sensitivity presents problems, since any time the predator moves, it stirs the water and is likely to scare off prey.  In the open seas, the solution for the predator is often to become the faster swimmer, but in shallows there are obstacles to speed, and other strategies are needed.  What seems to have evolved as a solution in shallow seas of the Devonian Era was for predators to become able to move by creeping along the bottom on modified fins while holding their spines still to avoid disturbing the water.  These modified fins gradually became limbs, and what had begun as a submerged aid to stealth gradually became a means of leverage for coming up on land, perhaps at first in order to lay eggs in a safe place.

            Once the creatures came on land, they faced a new problem: friction.  Without water to buoy them up, their bodies dragged on the earth and were hard to move.  This basic problem of terrestrial animals has two basic solutions:  either become very slippery like a snake or get more of the body off the ground to reduce the amount of contact surface.  Our ancestors took the second option and used limbs as levers to hoist themselves up from the ground.  To do this required them to use the spine in a novel way: as an arch of support between limbs.  What was novel about this was which way the spine had to be stiffened:  away from the earth and toward the back, rather than toward either side.  In order to stiffen this way, the entire length of flexory muscles on the belly side have to engage together, a situation similar to that of the primitive full thrashings of a threatened fish, except of course that the concave side of the spinal bend here is earthward rather than to the side.  The only fish I have observed that have even a hint of such ventral flexion are lungfish.  Lungfish are semiterrestrial.  So arched flexions toward the belly (or extensions away from it) seem to have originally been responses to being on land.  Of course, the early terrestrial vertebrates were in quite a different position from the early fish.  For one thing, they inherited what the fish had already evolved.  For another, they had limbs, and they seem to have emerged from the water having already limited themselves to four of these.

            Some attempts to move on land, observable in frogs, involved springing off of both hind limbs at once and onto both front limbs.  Essentially this involves using the whole spine as a single arch to throw the force of ground resistance from the tail end up towards the head.  For this to work, most or all of the body weight has to be vaulted up off the ground as the force passes through it. This is useful for speed, since it minimizes friction, but it is hard to sustain. Getting all the way off the ground takes a lot of energy.   Thus, frogs are quick when they move, but spend most of their time resting.  Animals like horses or cheetahs use this kind of motion only for their top speeds in galloping.  Perhaps the animals that use such movement most are the dolphins and whales.  For them, speed is also important, but getting off the ground is no longer a problem.  The similarity of their movement to that of fishes is only superficial.  The fact that they flex up and down rather than side to side betrays their origin as former land animals.

            Most terrestrials use their four limbs in some version of alternation from side to side, rather than only from hind to fore.  The simpler version of this, seen mainly in reptiles, involves resting the whole spine up off the ground on two arches, one formed by the forelimbs and shoulder girdle, the other formed by the hindlimbs and pelvis, sometimes with the belly dragging in the middle.  As the left hind arch leaves the ground to swing forward, so does the right front arch.  This makes the whole trunk between the limbs sway from side to side.  Thus the hindlimbs, for example, are still essentially being moved as a single unit, but rather than both being engaged equally at the same moment as they are in the leap of the frog, they are waddled along in alternation the way you might walk the feet of an upright ladder across the floor or the points of a drafting compass across a piece of paper.  Lateral swinging of the spine by itself could generate much of the momentum needed to swing a limb forward in this way, and could thus take advantage of the reflexes for lateral movement inherited from the fishes.  In this way, waddling on land built on the swimming of fish.

            How long this preservation of lateral flexory movement persisted through the evolution of reptiles is not known.  It is at least clear from the fossil record that the trend continued of rearing up away from frictional contact with the earth:  many dinosaurs became bipedal by evolving tails that were heavy enough to lever their heads and torsos up over the fulcrum of massive hip joints.  Whether they also slowly wagged their tails to aid their walking is less evident from looking at their fossilized bones.  But their general trend toward massive size suggests that their need for efficiency in locomotion might have been secondary to their need to reach and digest arboreal food sources high off the ground, more a matter of size and support than of speed or grace.

            The main structural change brought in by the dawn of the mammals was a fairly slight one:  the limbs were brought in from the sides to more nearly underneath the organism.  This of course required better balance in standing.  But in moving, the difference was greater.  Instead of waddling separate forelimb and hindlimb arches, the creatures that evolved into mammals made more use of diagonal arches of support, for example between rear left and front right, to free up the remaining two limbs to move independently.  This made it possible to eliminate much of the side to side waddle from walking, and to replace it with an alternating torque down the length of the spine.  The lateral wave of movement inherited from the fishes could then be replaced on land by a far quieter and more sustainable type of movement, but one that required more nervous system finesse to control.  This required a proportionately bigger brain, but it also needed less muscle.

            It can be seen now that when we look at lateral asymmetry in the human spine, we are not just looking at frozen lateral wiggles of a fish, though at some deep level such wiggles may underlie what we do see.  In humans that show no signs of scoliosis, the only vestiges of such movement lie in our bilaterally symmetrical appearance, in what we often perceive as human beauty, in which the symmetrical flexions of the fish have, as it were, come to rest.  But we have come far beyond fish, not only by the development of limbs and the venture with them onto land, but by the manner of how we have come to use our limbs, first as towers and arches of support to compensate for the loss of support by water, and then as more and more freely mobile intelligences that required less and less muscular effort but more and more brains to move.  In the more easygoing and sustainable versions of mammalian motion, the spine works mainly as a kind of torsion rod, and the torso musculature that surrounds it can perhaps best be understood as doubly spirallic (or rather helical) to accommodate such movement.

            This presents a new possibility in understanding the dynamics underlying scoliosis.  For it may be that what we see from the outside as merely lateral bulges are in fact more three-dimensional and helical than what catches our eye.  A simple analogy ought to explain this:  If you hold a strip of cloth at both ends and begin to twist it, at first you will only get a spiral pattern of folds down its length.  But if you keep twisting it further and further, a point will come when the folds can’t twist into each other any further, and the whole cloth will begin to bulge out it its sides in a helix, shortening the distance between its ends.  Scoliotic bulges seem to be of this sort, though the amount of twisting required to produce them is far less than in our example of the cloth, simply because cloth is softer and more twistable than vertebral bone.

The human embryo’s very first movement responses to a stimulus are ones of full lateral flexion, just like the primitive lateral thrashings of a beached fish.  At this early stage, the embryonic skeleton is still only cartilage, just as the skeletons of shark or dogfish are, these being earlier forms of fish before the evolution of bone.   The very first cells in a human embryo that are specialized for generating movement, the so-called somites, first appear in parallel rows on either side of the embryo’s midline, a bit like a double row of overcoat buttons.  This arrangement at first allows only for lateral movement, and may account for the earliest movement reflexes being ones of pure lateral flexion.  Once the laterally arranged somites are in place in the embryo, they divide front and back, giving rise to the basic separation in later musculature between flexors and extensors, i.e. between muscles that arch the organism into a forward tuck over its belly and muscles that straighten it back up or beyond into a back curve.

 We have already posited that the evolutionary development of flexion and extension in vertebrates was originally a response to getting their spines propped up off of land onto limbs.  Is there any correlation between an embryo’s first flexions and extensions and the first budding of its limbs?  Is this preceded by the beginning of skeletal ossification, since bone in fishes long preceded the first invasion of land by amphibians?  Do these developments correlate in any way to the development of lungs, another evolutionary adaptation that may have originated in water but was essential to the invasion of land?  And does the embryo in any way learn the subtler lateral waves of fish movement prior to its first onset of flexions?  It is very difficult to get a clear view of the evidence on these matters, since so much of it lies within the inviolate privacy of the unborn child’s explorations of movement within its mother’s womb.

            It does appear that the onset of idiopathic scoliosis is not just a matter of malformation of the vertebrae, or even of distortion of ligament or muscle length, but rather intimately involves how the brain interprets the sensory input it receives as it guides its owner into movement.  The locomotory apparatus obeys the instructions it receives, and gradually becomes distorted when those instructions go awry.  That it should distort itself toward more primitive patterns of reflex perhaps only shows how delicately those patterns have become neutralized in the human nervous system, and how easily a disturbance to that system can elicit a throwback or a regression.

            What does all of this say about how scoliotic deterioration might be slowed down or reversed?  Well, obviously, the scoliosis has to be noticed, so observation and diagnosis have to come first.  But beyond that, if indeed a scoliosis represents an erosion of the organism’s ability to neutralize the thrashes and twists of more primitive kinds of locomotion, then reversing such erosion must to some extent mirror the process by which such movement was refined in the first place.  A learning process would have to be involved.  Like all mastery of movement skills, much of what must be learned is what not to do, what superfluous expenditures of energy can be omitted.  This fits with our observation that increasingly efficient movement tilts the ratio of excitation to inhibition toward the latter.  In other words, the movement must be taught to find a path of greater calm and ease.  And as we also noted, finding such a path of less effort requires a greater investment in central nervous system control.  So in addition to greater calm, it would also require more thought.

            Such an approach to a disability sounds more like Eastern meditation than like physical therapy, but it must if it is to take the contributions of the nervous system into account.  Indeed, Eastern traditions of martial arts or yoga have vast traditions of training the mental aspects of movement, while too crude a version of mechanics still dominates rehabilitation in the West.   Happily, there is a growing field of exceptions to this generalization, each of which includes deeply articulated practical skills for bringing relief to the structurally disoriented.  Raymond Dart’s students have explored the evolution of movement skill in relation to weightbearing.  Bonnie Bainbridge Cohen and her associates have explored visceral contributions to scoliosis. Followers of Ida Rolf have developed skill in releasing distortions held in the fascial webbing that connects all organs, muscles and bones.  F.M. Alexander and his students have demonstrated how to use neural inhibition to retrain postural habit.  This list is only a gesture, not intended to be complete or do any justice to those mentioned, but only to suggest that they do exist, and that deeper exploration of the paths they have opened will amply reward those who have the courage to explore them.

 

                                                                                    Copyright 2003.

 

 

SELECTED REFERENCES

 

Bonnie Bainbridge Cohen. 1993. Sensing, Feeling, and Action: The Experiential Anatomy of Body-Mind Centering.

            Northampton, MA: Contact Editions.

Raymond A. Dart. 1950. Voluntary musculature in the human body: The double spiral arrangement. 

            The British Journal of Physical Medicine. Vol. 13, No. 12:  265-68

Reprinted in Dart, 1996, Skill and Poise, London: STAT Books.

Kenneth Kardong. 2002. Vertebrates: Comparative Anatomy, Function, and Evolution.

            New York: McGraw-Hill Higher Education.

Thomas Myers. 2002. Anatomy Trains: Myofascial Meridians for Manual and Movement Therapists.

             London: Churchill Livingstone, Harcourt Publishers, Ltd.

Michael Newirth, M.D., with Kevin Osborn. 1996.  The Scoliosis Handbook: A Consultation With a Specialist.

            New York: Henry Holt & Co.

F. Harvey Pough, Christine M. Janis, John B. Heiser. 1999. Vertebrate Life.            

           Upper Saddle River, NJ: Prentice Hall Inc.

Leonard Radinsky. 1987. The Evolution of Vertebrate Design.

            Chicago: The University of Chicago Press.

A.G. Veldhuizen, D.J. Wever, P.J. Webb. 2000. The aetiology of idiopathic scoliosis:

            Biomechanical and neuromuscular factors. Europe Spine Journal. 9:178-184.

Carl Zimmer. 1998. At the Water’s Edge: Macroevolution and the Transformation of Life.

             New York: The Free Press.