A lumbar vertebra stationary in mid-position is balanced over the core of the intervertebral disc, the weight of the body pressing down in front of this, the pull of the muscles drawing down behind.  Over this as a center of balance, axix of motion, or fulcrum of leverage, flexion and extension occurs by relaxation and contraction of the spinal muscles, by sliding out (flexion) and in (extension) of the articular surfaces, and by compression and decompression of the remainder (front part) of the disc.
 
 
LIMITATION TO MOTION

    Limitation to the proper motion of extension occurs from the tensing of the anterior longitudinal ligament and possibly (rarely if ever) of the disc itself; and by bony contact (through intervening tissue) of the lower edge of the upper articular process of each joint (inferior articular process of the vertebra above) with the lamina of the bone below.  The capsular ligaments, loose enough to allow of free flexion and rotation, are probably loose enough to play little part here, or even to allow separation as noted below.

    Further motion can occur only be separating the articular surfaces and further stretching of the anterior ligaments.  This,  however, can occur if the bony contact permits of sliding, the ligament acting then as a radius of the further motion, and giving rise to secondary motion.  It draws down the anterior edge, allowing the whole bone to move posteriorly with separation of articular surfaces.  Into the vacuum thus produced capsular ligament may perhaps be forced by atmospheric pressure, especially at the lower edge.  Lesion is thus produced, which, (except in warped conditions) in all likelihood corrects itself, as the forces tending to the normal are overwhelming and as there are no forces ecept position helping to maintain lesion.  When maintained, it is an extension or approximation lesion.  Approximation lesions (except in warps and secondary to separations above or below) are rare.

    Limitation to the proper motion of flexion is from the tensing of the posterior longitudinal ligament, the interspinous ligaments and the capsular ligaments, and from compression of the disc in front.  The disc is the softer of these, so the chief checking influence is the ligaments behind.  Of these ligaments, the ligamentum flavum (posterior surface of spinal canal) is of yellow elastic fibres, and so highly elastic, being at the same time close to the axis of motion.  The interspinous ligaments are not disposed longitudinally, but pass forward from top and bottom of each spine at about 45 degrees.  That is, as in all cases uniformly throughout the whole body, they lie radially to the motion of the bones they hold (longitudinally to the direction of tension, radially to the direction of motion) so that they re tense at all times; and so that at the limit of their motion, a very slight stretching will allow comparatively great further motion; with increase in tension in proportion as they are inelastic.

    Beyond this point further motion can occur in cases of violence by the stretching of these ligaments.  A change in the angle of motion occurs, though to a very slight degree, limited by the shape of the articular surfaces.  The upper half of the articulation (inferior articular process of the upper bone) passes beyond the edge of the lower, assumes an angle with it, and receives an indentation from its upper edge, meanwhile being driven against it with great force by the stretching of the interspinous and other ligaments, all of which force the bony contacts against each other and increase the dent, and serve to retain it in that position as a lesion.  There is gapping of the lower part of the articulation, and compression of the disc.

    This secondary motion with lesion we may well believe rarely occurs in the median line, although median lesions—separation lesions—are sometimes noted here; for the reason that in the median line all of the ligaments are at their most favorable angle and all acting together, and tend to prevent the occurrence of lesion.  When in extreme flexion, however, some other motion, as rotation or side-bending, occurs, then these ligaments cease to act together, one or two are easily stretched, and great danger of lesion arises.  Then, by the very relation of the articular surfaces, one corner or edge of one side is forced at an angle against the opposing surface, making under the heavy pressure a more acute indentation, from which it may be unable to release itself unaided.

    The proper motion of rotation in the lumbar region is in reality side-bending rotation.  This fact we have already noted; it is due chiefly to the action of the anterior spinous ligament which, immediately the body of the vertebra has moved from the median line, acts to produce a motion of which it is a radius; drawing down the anterior edge and transforming rotation into rotation-side bending (and we might add, flexion also).

    From the position of extreme extension, rotation-side bending is accomplished by lifting of the articular facet of the convex side.  Since even in this extreme position—indeed especially in this extreme extension, the anterior ligament also acts, any rotation becomes rotation-side bending.  The result is that the articulation of the convex side is not only lifted, but moves forward; and in the opposite one (still at lower limit of motion) moves back and twists.  This bring the lower edge of the inferior articular process (upper of the two in each joint) on the convex side against the surface of that side with indentation and possibly lesion.  Lesion in this position is comparatively rare except from continuous warping with weakening of ligaments; for the reason that there is not sufficient edge on the articulation, no sufficient stretching of elastic ligaments in this position to maintain the angular pressure against the surface, and such lesions usually correct themselves.

    From the position of extreme flexion, rotation does not occur (except from a yielding of all elastic tissues).  From this position, side-bending occurs by receding of one articular surface.

    This, however, immediately becomes rotation-side bending.  This occurs by the depressing of the articular surface of the concave side, with sliding back, on the concave side and forward and in on the convex side, and tortion on both sides.  The least exaggeration of this motion causes a change in the angle of motion which immediately brings the lower edge of the upper articular surface on the convex side into contact with the opposing surface of that side, with indentation and possibly lesion.  As one recovers from such a position, unless he recovers the rotation before he recovers the flexion, lesion is very likely to persist.  The concave side of the lesions moves toward normal, increasing the angle and the indentation on the convex side.  The weight of the body descends and fixes it thus.  There is no normal tension here leading to correction which does not also serve to maintain the lesion.  The majority of lesions (except warp lesions) are of this character.  They may be compared quite accurately to a bureau drawer which has become jammed.

    Rotation in the median position is, as said, transformed almost immediately into rotation-side bending, through the action of the anterior longitudinal ligament.  The motion is radial around this ligament, as to side-bending; as to its rotation, it is radial around a point posterior to the articular surface, perhaps to the tip of the spine itself.  Examining and experimenting with the actual bones makes the forming of a mental picture of this motion easier.  Across the top of the body of each lumbar vertebra, near the back, is found a shallow groove which just about fits the finger tips.  This groove is curved, concave backwards.  Its curve is sharpest in the third vertebra, less and less in the fourth and fifth as also in the second and first.  This curved groove points fairly accurately to the center of rotation of the vertebra above.  It is the groove through which moves the core of the intervertebral disc as each bone rotates on the one below.  The difference in the arcs of those grooves verifies the work done by the classes referred to above in reference to centers of rotation of lumbar vertebrae.

    The cores of intervertebral discs then become important.  These cores are found nearer the posterior margins of the discs.  They are more solid than the rest of the disc, and act on the principle of ball bearings.  They are therefore necessarily fulcra for all motions of the bodies on each other, except that of rotation, because in rotation they themselves move, making this groove.  In equilibrium of the body the line of weight passes in front of them, and in the median line; and the pull of muscles is behind them, but also (through transverse processes) on either side; all acting downward; so that this core is the teter of the balance.  In flexion and extension it is the teter, the axis of motion, until limitation to motion arises at some other point.  In side-bending it is also the axis of motion, which passes through it antero-posteriorly, also until limitation of motion occurs at some other point; when of course that limitation forms part of the axis of the motion.  The axis, that is, passes through the core and the point of limitation. K But in rotation it is merely a ball bearing on which the bone rolls.  The body above immediately passes from its central position over the core and tilts; hence also side-bending; but it also carries this core with it, as in a ball bearing joint (since the core is fastened to the base above as well as to the surface below), hence the rolling motion of the rotation-side bend.  But we must not forget that also the core is squeezed to the convex side by the pressure from the inclined plane of the base above; qualifying this motion; mbring it about that the greatest possible amount of effective side-bending is produced with the least possible extension of muscular tissue (as universally in the body).

    In rotation-side bending, from the median position, the articulations of the concave side slide in (extend) before those of the convex side slide out (flex).  Why?  This is due chiefly to the action of the intervertebral disc, which is immediately squeezed to the convex side as soon as there is any tilting of the surface; hence without raising the convex side, it lowers the concave side.  Remember also that the muscles that maintain the balance of the vertebra are in action continuously, and any change that involved contraction or shortening of muscle is likely to occur first rather than one that calls for stretching of it.  Hence again, extension occurs first.  The axis of this motion becomes therefore a line drawn through the intervertebral core and the articulation of the convex side; and it swings as this core moves.

    Around this axis  rotation  side-bending occurs first by depression of the articulation of the concave side, doubtless to varying distances in different persons and under different conditions; possibly until limitation to motion on that side is encountered; then by elevation of the articulation of the convex side; the axis now being a line through the core and the opposite articuilar surface.

    (Again note that this agrees with the results of the work done by the classes referred to, where it was found that the two articulations of the lumbar vertebrae had not the same center, but that the center of rotation of each was a point posterior to the opposite articular surface, approximately; wider in the lowest, less wide in the upper, coinciding opposite the eleventh or the tenth dorsal, whose discs are so thin as to preclude such motion.)

    This principle, the moving of one side at a time, is vastly important in correction of lesions.  It enables us to use one side as a fulcrum for the disengaging of the other side.

    The actual amount of rotation-side bending in single joints is slight.  But as the normal amount of actual  motion is slight, so is the amount of excess necessary to produce a lesion slight; and this motion is just as important as though it were wide.
 

MECHANICS OF LESIONS

    Limitation to this motion of side-bending-rotation of lumber vertebrae from mid-position is from compression of the disc, and tension of practically all ligaments, chiefly the anterior longitudinal, the capsular and the inter-transverse.  These limitations doubtless arise all at practically the same time.  We may add, perhaps, bony contact (through intervening tissue) on the concave side.  Under these limitations to motion the character of it changes if further motion takes place under force, the articular surfaces assume angles with each other so that (in rotation to the right) the superior edge of the lower articular surface on the right and the inferior edge of the upper articular surface on the left are engaged against their opposite surfaces; with indentation and danger of lesion; from which spontaneous recovery is not difficult because ligamentous tension from the inter-tranverse ligament of the convex side, drawing outward and downward, tends to release the catch; but which may remain as a lesion.  It is when to the tangle in this extreme position some other excessive force is added, as flexion, that danger of lesion is great, and spontaneous recovery is difficult.
 
 
MENTAL PICTURES

    To form a mental picture of limitations in extension and flexion, the student should use the technic described in Chapter IV, p 45, slightly exaggerating the motions.

    To form a mental picture of side-bending-rotation, the student should first experiment with the actual bones, then  with these bones using elastic bands in place of ligaments (although it is not possible to arrange these bands just as the ligaments in the body are arranged); and should then use the living body.

    To form a mental picture of side-bending-rotation in the living body:

    (This technic has been found to be invaluable therapeutically, especially in cases of constipation; in about 15 per cent of the students treated thus, results were immediate):

    Patient seated on table; operator standing behind; places right axilla over right shoulder of patient, grasping left elbow of patient, whose upper arm should be held about vertically; with left thumb operator prepares to press against the right sides of the opinions processes of each lumbar vertebra in turn, beginning with the fifth.

    The point in executing the movement to be described is to keep the shoulders parallel with the edge of the table (no rotation) and also with the surface of the table (no tilting) while moving them and the trunk with them to the left; so focusing all motion on the vertebra against which the thumb is pressing.

    Operator now moves patient’s shoulders directly to the left, allowing weight to descend on right shoulder and lifting on left through the arm; at the same time pressing with the thumb against the fifth lumbar spine so as to carry that vertebra to the limit of its lateral excursion; which requires that the right ischium should be lifted completely from the table; all of the side-bending being thus concentrated on it; and so of each lumbar vertebra in turn.

    When the limit is reached, a definite check is felt; some further pressure should be exerted to stretch the ligament.  The operator will then note that the costal and transverse processes of the concave or right side have moved far forward and are approximated to each other; while those of the convex or left side are prominent posteriorly and separated.

    (At the limit of side-bending-rotation, or before, there is a strong natural tendency to flex the body as a whole.  Note that the limit to pure side-bending is naturally at the costal and transverse processes, at the center of the side; further motion is then possible only by turning one way or the other, with separation of the bodies or of the spines; of which nature prefers the latter, with flexion.)

    Now if in this position of extreme side-bending-rotation he will extend the spine, he will note that the processes of the right side retreat still further; if he flexes the spine, he will note that they reappear again posteriorly.

    The student should make a number of different experiments with the motion of lumbar vertebrae under different circumstances, as for instance the following:

    Patient seated on table; inclined slightly forward.  Operator stands behind, passes right arm under patient’s axilla and places right hand on patient’s left shoulder:

    Then places thumb of left hand on right side of spines of each lumbar vertebra in turn, in such a way as to feel two at the same time; places fingers of same hand on and between costal processes of these same vertebrae.

    Operator then first swings shoulders so as to produce normal rotation-side bending, noting motions of spines and costal processes.

    He then swings shoulders so as to produce rotation only, by raising up on right shoulder and pressing down on left at same time that he rotates.  The total amount of excursion is observed to be very much less.

    Or, operator may place knuckle of left first finger on left sides of spines, with thumb extended along right costal processes; executing same movement.

    Or, operator may place his right axilla over patient’s right shoulder and grasp patient’s left elbow with right hand, pressing instead of lifting in producing rotation.
 
 
DIAGNOSIS

    If a spine is in the median line and equidistant from the spines above and below, it is hardly possible that lesion exists.  For it is hardly possible that a spine will be bent in one direction and in lesion in exactly the opposite direction and to the same distance.

    There exists a variety of lesions that may be called masked lesions, in which the deviation is not evident in one position, but is in another.  In the sitting position it may be drawn to the median line by tension of surrounding parts, but become apparent in lying prone, or on one side.  Especially may lesion be masked when lying on one side, but become quite apparent when lying on the opposite side.

    When deviation is observed laterally or longitudinally, it may be due to bent spine or other irregularity, to a very freely moveable vertebra, to compensation for some other lesion, or to lesion in the vertebra itself (lesions are always reckoned with reference to the vertebra below; thus a deviation between the third and the fourth is a lesion of the third).

    Examination must then be made for other signs of lesion.  These are restricted movement (not necessarily absence of movement), tenderness, contracture and visceral disturbance.  In an experience of over fourteen years I have not found these signs always present by any means, since functional compensation may have removed them; nor have I found that their absence proves the non-existence of lesions; nor have I found that their presence proves lesion, since they may all arise from reflex irritation due to strain of some function whose nerves center at that point.  The best proof of a lesion is that it can be corrected.  Remembering that lesions are easy to correct (usually) and hard to create, one seems justified in trying to correct any deviation.  If it   resists corrections that is one evidence that it is a bony abnormality and not a lesion.

    Limitation to motion is the most reliable of the accessory signs of lesion.  Perfect freedom of motion proves the non-existence of lesion, but practically this is very hard to determine.  In most lesions, lateral deviation plus longitudinal separation plus limitation of motion exist at the same time, and the direction of the deviation corresponds with the character of the limitation to motion.  In a third lumbar vertebra deviated to the right, there will be found separation also, as a rule; in complete flexion of the spine the lateral deviation may entirely disappear, and in extreme extension it may be aggravated.  This defines the limitation to motion—the extension is limited on the right side.  This combination of evidence practically proves the existence of lesion.

    In examining for lesions we are limited to digital exploration.  As  yet no method of mensuration that is effective has been devised.  The use of the tape line has been tried and has given many results that cannot be explained as yet.  The tape should be fixed at the spine of the seventh cervical vertebra, and the reading at the lower margin of each spine should be recorded.  The interval from each one to the one below should be then recorded in eighths of an inch, discarding the denominator.  An easily read record is then obtained.  This should be done first with the patient erect, and then again with the spine fully flexed.  Lateral deviations are easily and accurately recorded by means of the tape in the exact center.  It is then found that the longitudinal deviations are more numerous than the lateral ones.  Limitations to motion are easily noted by comparing the two records.  In quite a large number of cases it is found that the interval between spines is actually diminished instead of increased in flexion—a positive reasons for which cannot now be given.  The difficulty with this method is that it is not technically accurate.  Some study should be given to this problem.

    It  has been recommended that examination for lesions should be made at the transverse processes rather than at the spinous processes.  Except in very thin persons this is difficult or impossible on account of the overlying muscles and fat.  It also is subject to the same uncertainty that forms the chief difficulty in diagnosis by the spines—irregular transverse processes also occur, though perhaps not so frequently.
 
 
TECHNIC

    Scientific technic must necessarily be based on two factors; the first a scientific examination of the mechanics of the articulations and their movements and the etiology of lesions; and the second a practical study of the methods that have worked out best in practice.  No theoretical science in the world is so perfect that it can come to practical success without practical testing.  There is always more in the fact than can be determined in theory.

    Practical experience, which in this case was worked out independently of theoretical examination, has, however, worked to the same end.  The two agree.

    The majority of lesions of the lumbar region are warp lesions, to be cured by posture and exercise.  But in this case the technic that is effective for warp lesions is also effective for the majority of lesions in the more strict sense, single acute lesions; which by contrast we might call radical lesions, major force lesions, traumatic lesions.

    The problem is to disengage the lesion at the indentation, where it is caught, and to move it toward the normal.  In order to do this, the problem is to so apply force and to so control the two bones involved as to move them beyond the point where they were at the moment that the lesion was formed; or by leverage to release the catch; and in such a way that immediately upon the release they will assume normal relationship.

    The majority of major force lesions of the lumbar region occur in extreme flexion with rotation to one side.  The problem then is to so carry them to extreme flexion again that the rotation will be overcome, the catch disengaged, and in the same act they will be carried to a position from which they naturally recover mid-position.

    Assume lesion of third lumbar, catch on right, spine deviated to right.  Have patient seated on table, operator standing behind.  Operator places “heel” of left hand against two bones in lesion, slightly below tip of spine of third; rotates patient slightly to right, so that in next phase he can rest elbow on table behind; passes right arm over patient’s right shoulder, grasping left elbow, and draws patient back against wrist of left hand, left elbow descending to table and bearing whole weight; patient should be thoroughly relaxed, resting on operator’s shoulder, head resting on operator’s neck.  Operator then lifts with both hands directly toward patient’s head.  Correction will usually then occur.

    Mechanics:  All vertebrae of the spine are thus in extension except the ones against which the hand is lifting, which are in flexion.  The traction on the spine above lifts and draws back on the third vertebra; the pressure over the right wrist throws it into flexion; the drag of weight acting through the ligaments draws the lower of the vertebra (fourth) away from it until it is straight, and the catch is released; and immediately carries the upper articular surface against the lower in such a way that normal relation is immediately reassumed and the lesion corrected.

    If the lesion is very much rotated, say to the right, the operator may slightly exaggerate the turning to the right, to secure rotation of the third to the left.

    This technic is available from the fifth lumbar to the mid or even the upper dorsal vertebrae, and is effective for rib lesions as well, though some caution must be employed in applying it to rib lesions in delicate persons.

    Caution.  The mistakes commonly made is this technic are first in drawing the patient back against the hand instead of lifting toward patient’s head with both hands; the result being that the violence of the lesion is increased.  Second, the operator may unduly stretch the skin over the spines by allowing the hand to slip upward on the spine, thus causing considerable pain to the patient.

    In very heavy persons some pain may be caused to the operator’s wrist unless caution is employed, until the wrist has been accustomed to the strain.

    A second form of technic may be employed, utilizing the sound side as a fulcrum by which to release the engaged side.

    Patient seated on table, operator standing behind; places thumb against prominent side of spinous process of vertebra in lesions.  Assuming lesion to right, places left thumb against right side of spinous process, prepared to exert pressure toward left.  Operator passes right hand under patient’s right axilla and grasps left shoulder; allows patient to flex spine, leaning slightly forward, operator sustaining part of weight; presses down on shoulder until lumber spine is bent back to full flexion.  Operator then rotates shoulders to right (forward on left, backward on right), lumbar spine moving to left, to full rotation; presses with right arm to secure both full flexion and full rotation.

    Mechanics:  At limit of motion, the left articular facet of the vertebra in lesion reaches a fixed point, restrained by capsular and other ligaments, at extreme upper part of excursion, pressing against opposite articular surface in direction  forward and to left.  Further motion in this direction, acting against this as a fulcrum, draws right articular surface (the one in lesion) backward, upward and to left—disengages it.  Operator produces such motion by further rotation with firm pressure downward on left shoulder, lifting the right if necessary; and exerting smart pressure with thumb against vertebra in lesion.  Note.  In order to make firm and steady the pressure with the left thumb, it is often convenient either to plant the fingers against the flesh at the proper dist ance, or else to anchor the knuckles of the first finger against the opposite side of the spine below, the lower of the two in lesion.

    The “Corkscrew” motion may be employed in the gentler “heavy barrel” technic.  It is produced as follows:

    Patient seated on table, operator standing behind; places left hand of patient on right shoulder; operator places axilla over right shoulder and hand lying thereon, passes right arm under left elbow of patient, against chest, places hand under left axilla, grasping left shoulder from beneath.  Thumb of operator’s left hand rests against right side of spinous processes, knuckle of first finger against left side of one below, prepared to press forward and from side to side.

    Operator then draws patient toward him (standing at rear and to right of patient); then with elbow pressing against patient’s chest, presses the spine back to full flexion; then transforms flexion into side-bending to left by pressing down on right shoulder while lifting on left, pressing also with thumb to left; then transforms side-bending into extension by pressing down on right shoulder while lifting on left, pressing also with thumb to left; then transforms side-bending into extension by pressing forward with thumb while shoulders are retained in mid-position; and again transforms extension into side-bending to right by lifting on right shoulder, pressing down on left, and drawing lumbar spine to right.  This motion is then repeated more rapidly until it is sure that patient is thoroughly relaxed.  Then turning patient gradually more and more to right to limit of flexion and rotation while the corkscrew motion is kept up, the mechanics of the previous technic becomes effective and the lesion is corrected.

    Innumerable different forms of technic are in use throughout the profession.  These illustrations will serve to show the application of the mechanical principles factors in correction at the time they are occurring.  These things should be rehearsed until they have built themselves almost into the subconscious thought of the operator.  There are enough factors in a treatment that claim the conscious attention; and all that could be should be so rehearsed that they will be easy under any circumstances.  Only thus will their operation be sure.
 
 
DORSAL REGION:  MOVEMENTS

    There is slight movement of flexion and extension in the dorsal region, but except at the lower two or three dorsals and the upper two dorsals it is very slight.  With the spine in erect position and the hand on the head causing passive flexion and extension, this is felt more as an elastic yielding than as a motion; it being remembered that the spinous process, twice as long as the distance from axis of flexion (Articulation of rib) to articular surface, moves twice as much as the articulation itself.

    The axis of flexion and extension is the head of the rib where it articulates with the lower facet of the vertebra.  This was well shown by Mr. (now Dr.) Louis E. Browne, in the class referred to.  The narrowness of the disc itself shows how slight is this flexion and extension, as does the fact that the articulation at the head of the rib is not shaped for such motion at all, arguing only a slight elastic yielding at the axis of motion.

    Rotation of the spine as a whole occurs in the dorsal region.  In extended position it occurs almost wholly in the lower dorsal and upper lumbar vertebrae; in erect position in the lower dorsal; in semi-flexed, in mid dorsal; in flexed position in the upper dorsal only.  The factor or at least one factor determining this may easily be shown; it is simply that when in the fully flexed position of any vertebra rotation occurs, it is accomplished by the extending of one side;  that is it involves extension; and cannot occur if flexion is fully maintained.  Flexion occurs first in the lower vertebrae and last in the uppermost ones, therefore rotation is lost first in the lower dorsals and last in the upper dorsals.

    Movements of rotation in single vertebrae are also very slight.  This is indicated by the smallness of the articular surfaces, by the way in which the inferior articular surface from the bone above overlaps at its edges the slightly smaller surface below (indicating motion restricted to the larger surface) by the smallness of the articular facet of the rib (which is the axis of flexion and extension but not of rotation and must also move in rotation) and by the limitation set by the tissues surrounding the ribs.

    Nor is it probable that movements of rotation are pure, but are compounded of rotation and side-bending to probably equal degrees, especially as we approach the limits of motion.  This is indicated by the costal facets and by the shape of the upper articular surfaces.  Although the costal facets are so placed that they could allow a slight degree of rotation in the horizontal plane around an axis near the center of the body, by pushing the rib down on its inferior facet; yet the place of the facets indicates motion at an angle of about forty-five degrees from the horizontal.  Direction of motion being determined by the articular planes, that of dorsal vertebrae would be in the direction common to the two planes of the facets and of the spinal articular surfaces themselves, which is about forty-five degrees up and forward.

    Now if we will examine the actual bones we will observe that the facets on the lower borders of the vertebral bodies, (those for the upper facets on the heads of the ribs) are the best formed and defined; they are the ones on which motion evidently occurs; while the facets on the upper borders (those for the lower margin of the head of the rib) are evidently those by which the ribs adhere to the bones (the rib belongs with the lower of the two bones; being a branch from the upper edge of each segment; as proven by analogy with vegetable forms, by the eleventh and twelfth ribs, and by the joining to the transverse process of that vertebra.)  Motion occurs at both of these facets ins respiration and other motions of the ribs; sometimes doubtless in motion of the vertebrae themselves.  But it is evidently the facets on the inferior border that determine ther motions of vertebrae.  Placing the finger then in such position that it is flat against both of these articulation, (costal and spinal) it will be found that it points up and forward and out; up at an angle of about forty-five degrees in the lower dorsals, the angle growing less until it is almost horizontal in the third or fourth dorsal, and is practically lost on the second, the costal surface being there not a plane but often a cup-shaped surface, showing little or no motion; while on the first dorsal the articulation is altogether with the first dorsal and not at all on the seventh cervical.  This angle determine the amount of side-bending, which is greatest in the lower dorsal and is lost in the upper dorsals.

    The forward angle of the pointing of the finger (indicating angle of rotation) likewise changes.  In the lumbar region, as said, it is backward; in the twelfth dorsal it is also backword; in the eleventh usually directly outward; in the tenth slightly forward, more so as we ascend until about the fifth, when it changes again until in the second or first it is directly out, or may point even backward; such vertebrae having no rotation at all, but only unilateral flexion and extension.

    This again coincides with the work done in the classes of the A. S. O. referred to, where it was found by all students that the centers of rotation were in front of the articular surfaces in the dorsal region; were farthest away in the lower and upper dorsals, nearest in the mid dorsals where rotation was greatest and sharpest; the center being at infinity in the eleventh or tenth and in the second or first, being for the most part near the front of the body of the vertebra in the average mid-dorsal vertebra.  Except that in many spines examined the centers of rotation of the upper dorsal vertebrae were extremely irregular, on account of the extremely slight degree of true rotation in that area.  In those vertebrae whose centers of rotation are at infinity there is of course no rotation; but rotation of the trunk is nevertheless aided by unilateral flexion and extension (the articular surfaces being sloped forward).  In such vertebrae it is to be noted that the rib does not articulate with the vertebra above, but has only the one facet on the body.

    A curve formed by continuing the line of the pointing fingers on the two sides inward until they meet would define the arc of movement of the vertebra.  This arc points up and out and forward on both sides.

    A further illustration of this side-bending-rotation is found in the shapes of the superior articular surfaces..  Rotation up and out and forward would naturally cause the upper and outer corner of the superior articular surface to be bent forward.  Examining the articular surfaces we find just this to be the case, at least in the lower three or four vertebrae, where the articular surfaces are bent like propellar blades; and this is apparent chiefly in these lower vertebrae because it is here that side-bending chiefly occurs.  All motions are less in the upper dorsals; among other reasons on account of the shortness of the ribs.

    The best way to fix these facts in mind is to make practical use of them.  Note that a strain beyond the normal is likely to affect different parts of the spine according to direction of the force.

    Strain of rotation in ;the erect position is likely to be felt in the lower dorsals; in the semi-flexed position it is felt in the mid-dorsals; in the fully flexed position it is felt in the upper dorsals; and anyone may quickly and easily test this matter in his own body.

    The greatest danger of lesion is where the limitation to motion is greatest.  It is a mechanical law that there is a point of mechanical weakness where a large part joins a small part; as in a nail driven in a wall, the nail will bend just where it leaves the wall.  Danger of rotation lesion is therefore greatest just at the upper and of the part that is locked against rotation by flexion; lower down in extension, higher up in flexion.

    To focus corrective force of a rotary nature on the lower dorsals, the upper dorsals should be kept straight, as by means of an arm under the chest.  To focus it in the mid-dorsals the lower dorsals should be flexed, the upper ones extended, as in bowing of the spine while the head rests on the folded arms.  To focus it on the upper dorsals, the head and neck should be used as levers protected against injury by the supporting hand on neck, while the spine below the point treated is flexed.

    Lower dorsals are carried to the limit of their normal motion by flexion-side-bend-rotation, mid dorsals by flexion-rotation, upper dorsals by rotation.  Strains of a different character have a tendency to produce lesions, especially if they occur at the limit of motion.

    In diagnosis, in exploring for limitation to motion, it must abe borne in mind that—

    It must first be borne in mind that individual skeletons vary and that much research and comparative study needs to be done on this point before safe generalizations can be made.  So far as such work has been done, it points to the fact that side-bending, or unilateral flexion and extension, is greatest in the lowest dorsals, that true rotation does not occur here but is greatest in the mid-dorsals, that practically all motion beyond a mere elastic yielding is often lost in the upper dorsals.

    It must then be borne in mind that one finds occasionally single vertebrae that have acquired such great freedom and width of motion that they are practically never in the median line, and when apparently in lesion to one side, move as easily to the opposite side with the least effort on the part of the operator.  These occur usually when there is abnormal limitation to motion above and below; and are found with greatest frequency at the eleventh dorsal, on account of the limitation to rotation in the lumbar spine which arises from the civilized habit of sitting or standing with the lumbar spine fully flexed.  Rotation does not occur in the fully flexed spine, so long as flexion is maintained.

    Side-bending is greatest in the lower dorsals and least in the upper dorsals, where it is practically lost.  A side-bending strain involving the whole spine will take effect chiefly in the lower dorsals.  If it involves the upper dorsals, however, it is much more likely to produce exaggeration of motion and so lesion.  Such a lesion is pretty sure to show itself as a unilateral flexion lesion, with rotation of the spine to side of lesion.  Measurement with tape line reveals that whenever there is lateral deviation there is almost certain to be separation, with compensatory approximation above and below.  Examination for limitation to motion is of very little value in upper dorsals.

    Side-bending corrective force is focused on different parts of the spine chiefly by pressure with the thumb; but also by different use of the muscles of the shoulder.  Keeping the shoulders well up tenses the long muscles to the lower dorsals.  Drawing the shoulders forward in mid position tenses the muscles to the mid-dorsals.  Drawing them down tenses the muscles to the upper dorsals.  Side-bending of the upper dorsals is however best accomplished through the head and neck.

    Taking up the point of the movements as determined by muscles, we discover the astonishingly simple fact that the costal facets on the inferior borders of the vertebrae point always toward the shoulders; being in line with the muscles that cause their motion.  Can further simplifyings be discovered of this character?  We find of course that the spinal articular surfaces are in line with the pull of the erector spine muscles; we find that they are concave toward the line of the center of gravity; we note that they are directly behind the base of the bodies of the vertebrae, and perpendicular thereto.