Two excellent aids in forming mental pictures are studying the motions in the animal spine, where they are easy to realize, and studying the mechanical laws expressed in the forms and the motions of vertebrae.

    In the animal body, the spine is suspended after the manner of the Brooklyn Bridge.  But the hind end (tail) has grown very small and thin, the front end has grown very huge, and added the City Hall for a head, and the Metropolitan and Woolworth towers for horns; so that the head and neck balance a large part of the trunk, and bring the major portion of the weight of the animal upon the front legs.  The front legs are therefore straight as all weight-bearing structures should be.  But the legs transmit this support through muscle and ligament to the upper ribs—wherefore in the animal these also are very nearly straight; and by consequence the upper part of the chest is narrow, which incidentally allows the forelegs to come close together and to be straight.

    What of the motions of these vertebrae and ribs?  They were evidently devised for weight and tension bearing first, and for motion second.  The movement of flexion and extension is performed almost entirely in the long neck—the joints in the upper dorsal part merely yielding a little; the motion of side-bending is the chief movement of these bones, as the animal walks on first the right leg and then the left; but that too is slight; the actual shifting of weight occurs by swinging the head—that is, almost entirely in the neck, with merely an adaptive motion in the dorsal vertebrae.  In walking, the dorsal spine side-bends slightly, becoming concave to the side which is supplying the support.  The center of this concavity is below the level of the spine, hence the centers of rotation of dorsal vertebrae are in front of the bodies.

    In the human spine the curve of the ribs has changed considerably, and the curves of the articular planes somewhat; but aside from that the inner conditions are practically the same, and the same conceptions of motion are applicable.

    In the mid and lower dorsal parts of the spine of the animal, the ribs serve as trusses supported by muscle and ligament and they in turn support the spine.  Motion grows freer as we move toward the lumbar region; but is still centred about points below the spine, or ventrally from the bodies of the vertebrae.

    The lumbar vertebrae, however, swing free; they are suspended from the dorsal spine in front and from the sacrum behind, and swing much as a hammock might, except that the central parts swing more sharply than the end parts.  As the right hind leg is lifted it bears the right side down; as it is drawn forward, the muscles at the same time bend the lumbar spine to the left, the bodies swinging farther than the spines. In the sagging curve of the lumbar spine, this produces just the motion that we have described, a sort of hammock motion in which the center bends farther than either end, the body farther than the spinous process.  The center of rotation of lumbar vertebrae is therefore posterior to the spine.

    In the erect human spine this curve is somewhat accentuated, but the difference is not so much as it at first seems; the differences is mostly in the legs and hips.  In any case, the same types of motion are observed.

    It is interesting, though not important, to note a few of the motions of the neck and the reasons therefore, in the animal as compared with the human neck.  The neck and head are supported by the ligamentum nuchae, which acts on the same principle as the long muscles of the thigh and leg—makes much easier, that is, the holding up of the heavy head, so long as the head is kept down and parallel with the dorsal spines, making a parallelogram with the ligamentum nuchae and the column of bone.  The cruelty of the check rein in horses lies mostly perhaps in the fact that it takes all tension off of this ligament, and throws the effort of holding up the hundred pouds of head and neck entirely on the muscles of the neck *note how the muscles around the root of the neck are developed in horses subject to check-reins).  In the grazing animals, it is the neck that must be long enough to reach the ground, hence the flexion motion is chiefly developed in the last cervical vertebrae, (in human subjects chiefly in the sixth, whose spine therefore disappears behind that of the seventh in extreme extension) so as to allow all of the length of the neck to be used.  The nodding motion is developed just at the back of the head, where it is most useful; the motion of rotation is developed as near the head as possible, that is, in the second joint from the head; far enough from the head to give effective attachment to muscles, and near the distal end of the neack so as not to weaken the structure of the neck itself.  These same conditions are found in the human neck.

    The second of the aids to realization spoken of is found in the mechanical laws that are expressed in the shapes and motions of bones and ligaments.  This is a subject for rational anatomy rather than for technic, but a few of them may be referred to here.

    The first of these laws is that bone always bears pressure, directly perpendicular to articular surfaces, and in the direction of the length of long bones, and of the grain of all bones.  This is true of even the curved ribs, and of the dome of the skull.  The shapes of bones is an absolute indication of the direction and degree of pressure that they bear, from weight from muscular and ligamentous action, from atmospheric pressure, from all possible sources.  There is not space here to expand that subject.  It is important in the development of a scientific technic, however.  For instances, the spinous processes of vertebrae bear pressure from muscular action and from ligaments.  The muscles that attach there are those of the shoulders, drawing up and out; they are opposed on the opposite side by the interspinous muscles in mid-positions, and by spinal ligaments also in extreme flexion.  The combination of these two is pressure on the spine in the direction of its length.  This direction proves to be almost parallel with the articular surfaces of the vertebrae, as it naturally would be, to admit the greatest facility of motion.  When, therefore, traction is put  upon these muscles, or on the ligamentum nuchae, its result is to flex the vertebrae to the limit, and, if unopposed, to produce lesion.  (It is when we consider two vertebrae together that we find this pressure in line with the spine transformed into pressure directly against the articular surface.)

    (The habit of having the patient clasp his hands behind his neck or head, passing operator’s hands under patient’s axillae and over patient’s hands so clasped, or his wrists, and jerking the head and neck forward with a lift of the body, is, in my opinion and experience extremely dangerous, causing more lesions than it corrects.  It almost invariably produces a “pop,” but the pop may signify the production as well as the correction of a lesion.  The reason for the producing of lesion is here seen.)

    To the transverse processes are fastened the muscles running from below, and pulling down and in, hence the up-and-out direction of these processes.  Whenever an articulation is moved to the limit of its normal play of motion, these muscles and ligaments are tensed, and the tension so produced may be easily calculated from the direction of the processes or the grain of the bone.  For the correction of lesions it is necessary to move them to the limit of their normal motion in order to get tension on them, so that these factors are of extreme importance.

    We seem to have contradicted ourselves in saying that pressure on articular surfaces is perpendicular to them, and then that the pressure from tensing muscles of the spine is parallel to them.  Let it be remembered that the tension of muscles does not stop with the bone to which they are attached, abut is taken up by other muscles of ligaments beyond.  The bone makes merely an angle in the tensions of the muscles.  The combined tensions bring pressure on the bones.  The case of the sacrum, already cited, is an illustration of this.  For the sake of building a clearer mental picture of articular surfaces and their relations, let us review more in detail the law mentioned, that when there are two articular surfaces on any bone, they are always perpendicular to each other; if there are three, these are all perpendicular to each other, like the corner of a box.  More than three there cannot be without making motion mechanically impossible; a fourth, if there is a fourth, becomes a cartilaginous joint, as in the costal cartilages.  The reason for this is extremely simple.  Let us repeat first that pressure on any articular surface must be perpendicular thereto or the bones would slide to the end of their possible motion and stay there.

    But suppose that an angular pressure is made; the articulation sustains all of the pressure that is perpendicular to it, and transmits the rest, as motion or as pressure, in a direction parallel to its surface.  If then a second articulation forms, its angle must be perpendicular to the first, for the same reason; and if a third forms, it also is perpendicular to the other two.  A fourth point of contact with bone must be able to yield in any direction governed by the other articular surfaces—hence a cartilaginous joint.  Illustrations of this law we find in the intervertebral discs, the costal cartilages, and also in the joint at the symphysis pubis.  Such a cartilaginous joint must also be found in or near the general plane of the other joints.  The symphysis pubis for instance is in the same plane with the base of the fifth lumbar, with the lumbo-sacral, and in a plane parallel with the articulation that is sometimes found on the dorsum of the sacrum opposite the second sacral spine, with the overhanging posterior superior spine of the ilium.

    At the heads of the ribs the two articulations are found to be perpendicular to each other, and the facet on the tubercle is perpendicular to both.  The costal cartilage is parallel to the last, the end of the bone itself in line with the intersection of the first two.

    At the heads of the ribs the two articulations are found to be perpendicular to each other, and the facet on the tubercle is perpendicular to both.  The costal cartilage is parallel to the last, the end of the bone itself in line with the intersection of the first two.

    The articulations of vertebrae are perpendicular to both the costal facets, and the fourth articulation, that of the base, is cartilaginous; it is also opposite to the other articulations, as in ribs and innimonate.  The extreme logical perfection of nature’s mechanisms makes us wonder and admire; but they do more; for these facts aid us in our osteopathic thinking, and indeed become the basis for scientific technic.

    The planes of articulation of the innominate are at the sacro-iliac articulation, vertical-antero-posterior; this being so rough and uneven cannot be considered as one plane, but includes planes tilted in and out; the (psuedo) articulation between the posterior superior spine and the second sacral vertebra, transverse-horizontal, tilted so as to be perpendicular to the base of the sacrum; and the symphysis pubis, cartilaginous, parallel to the sacro-iliac.

    The planes of articulation of the sacrum are the sacro-iliac, vertical-antero-posterior and uneven (to be considered therefore as more than a single articular plane), the sacro-lumbar, vertical-transverse (tilted so as to be perpendicular to the base of the bone) and the base, cartilaginous, transverse, perpendicular to the articular surfaces.  Pressure on the right side of the tail of the sacrum makes a fulcrum of either sacro-iliac articulation, whichever is the more rigidly fixed by ligament, and draws down on the left side, up on the right side (provided the corresponding ilium be fixed).  In lying on the right side, the weight of the body makes a fulcrum of the lower (right) joint, Traction through the spine on the sacrum acts at a considerable angle backward.  Against this fulcrum it draws ups and back on the upper (left) joint.  It will be remembered that the sacrum lies at a sharp angle with the spine, so that straight traction through the spine becomes dorsal traction on the sacrum.  Traction, plus posterior rotation of the left side of spine, however, greatly increases t he effect in drawing back on the upper (left) sacro-iliac joint.

    The planes of articulation of lumbar vertebrae are vertical-saggital, at the posterior portion of the spinal articulations, vertical-transverse at the anterior portions thereof; these articular surfaces are usually curved, concave in and back, the curve being great enough to include both saggital and transverse planes; though sometimes they consist of two definite planes as described, with a very short curve at the intersection, or even a groove marking the separation between them.  This description is approximate only, since the planes of articulation show usually a graded variation.  The articulation of the base, cartilaginous, is horizontal-transverse, also approximate, graded from forty-five degrees down anteriorly to a few degrees up anteriorly.

    With patient lying on right side, the spine of any lumbar vertebra being dixed, posterior rotation of the spine makes a fulcrum of the lower (right) articular surface, and is effective in gapping open and drawing up and back the upper (left) articular surface.

    With patient seated, complete flexion of the spine makes a fulcrum of the intervertebral disc and draws the articular surfaces out from each other; rotation added to this flexion makes a fulcrum passing through the base and the articulation of the convex side, and draws back and up the articulation of the concave side.

    The planes of articulation of dorsal vertebrae are the vertical-transverse, at the articular processes, vertical-transverse also at the transverse processes, the saggital forty-five degrees up and in at the superior costal facets on each side, (at right angles to each other), the saggital—forty-five degrees down and in at the inferior costal facets on each side, and the transverse horizontal (cartilaginous) at the base.  All of these planes are subject to graded variation.  The student should be familiar with these and should rehearse the various leverages and their effects.

    The planes of articulation of ribs are the transverse-forty-five degrees down and in at the superior facets, transverse forty-five degrees up and in at the inferior facets, transverse vertical at the tubercle, and saggital-vertical (cartilaginous) at the costal cartilages.  These are also subject to graded variation, as shown in the preceding chapter.  Pressure on the spinal   end of a rib makes a fulcrum of the resistant tissue surrounding the whole rib, and tends to gap open the articulation at the transverse process, sliding forward at the articulations with the bodies of the vertebrae.  Pressure at the costal end, if inward, makes a fulcrum of the head only, tapping open the tubercle-transverse articulation as a whole; if out, makes a fulcrum of the tubercle and slides forward the articulation at the head; if downward or upward it makes a fulcrum of the resistent tissue around the whole rib and has the reverse effect at the transverse process.

    The student should apply these principles to all articulations of the skeleton and rehearse them until thoroughly familiar with them.

    Having formed mental pictures of these motions and their laws, it then becomes important to realize them digitally, with the sense of feeling and of measurement.

    Have the patient seated on the table, operator standing in front; place towel or thin pillow on the top of the patient’s head and draw it against operator’s chest, against the gladiolus or upper part of manubrium; have patient place hands on operator’s shoulders; pass hands under patient’s shoulders, around patient’s body, fingers on tips or either side of spinous processes, beginning with lowest.  Draw forward with hands until joint is in extreme extension, (operator may bend or step back slightly) then pressing against head with manubrium, carry patient back to extreme flexion, feeling carefully the movements until familiar with all qualities of motion in the joint.  Then pass to next joint, and so on up the spine.  Then begin again with fingers this time on transverse processes, then on costal processes s(on ribs sin dorsal area).  Repeat again, making lateral movement instead of flexion-extension.

    This practice is very soothing to patients, is an excellent diagnostic method, and is corrective for slight lesions.  It may well be a routine practice with all patients, e specially in the beginning (it is a standard procedure with many very successful practitioners.  It originated, I believe, with Dr. Achorn of the Massachusetts College).  It is effective as high as the upper dorsals, and may be applied even to the neck.

    To become familiar with the normal movements of the heck have patient seated on stool or table, operator standing behind.  Place fingers on anterior corners of cervical vertebrae (costal processes) with thumbs on tips of spinous processes, gently or even loosely:  have patient flex and extend, rotate, and make all possible motions with head and neck, noting character of motion in vertebrae.

    The student should not fail of course to make note of character of motion in each joint of all patients at all times, as this varies in different spines and under different conditions of lesion and muscular contracture.  It should not be left to reason, but should be made a  habit; always making a moving picture in the mind of the actual position and relation of the bone.  The only proper osteopathic technic is to correct the lesion; and “We do not push bones into place, we think them into place.”  When we are trying to adjust a tone in lesions, we must “be that bone.”