Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them]

Chapter 14 On the Spine and its Various Bones 1

Key to the Figure which Follows, and its Characters
In the figure on the next page we have illustrated the spine [columna vertebralis], which is called by the Greeks a/xij and nw=ton, 2 from the side: first so that the structure of bones of the entire spine may be seen, and afterward so its individual parts may be shown in separate chapters. 3 Since the three figures that are placed at the end of this Book, especially the third of them, also illustrate the spine, you will do well to see them there in passing along with the figures of the third Book 4 illustrating the series of nerves originating from the dorsal medulla [medulla spinalis], placed at the beginning of the eleventh chapter of that Book.

A, B The neck, consisting of seven vertebrae [vertebrae cervicales] which are marked by numbers engraved next to their inner surface.
C, D Portion of the spine making up the thorax [vertebrae thoracicae], which many have simply called the dorsum. Others, because it is located as it were behind the transverse septum, call it the metaphrenum; others, as we were just now saying, the part of the spine where the thorax is. This is most often made up of twelve vertebrae, to which the ribs [costae] of the thorax are articulated; whence they are also called the costal and thoracic vertebrae. 5
E, F Portion of the spine constituting the five lumbar vertebrae [vertebrae lumbales].
G, H The sacrum [os sacrum], which you will grant is fashioned in humans of six bones or vertebrae 6 after I have completed my separate description of the sacrum.
I, K The coccyx, which you will also agree is made up of four ossicles 7 when I shall have described it too.

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L, L, etc. We have marked some vertebrae L, to wit the second, ninth, eighteenth, and twenty-fourth, to indicate the part or region of the vertebra which we call their body [corpus vertebrae].
M, M, etc. This letter is seen on the same vertebrae where L occurs, marking the processes [processus transversi] extended to the sides, and hence called by us transverse or lateral. I believe no one will fail to see that in fact the vertebrae marked L are not the only ones with a body, and those marked M not the only ones with transverse processes, even though I have not covered every vertebra with letters. This was our judgement about the identifiers that follow; if something applies only to a single particular vertebra, we have decided not to explain it in this chapter. 8
N, N, etc. You will observe an N on the eighth vertebra of the whole structure of the spine, and on the seventeenth and twenty-third. This letter marks certain processes [processus articulares inferiores] of the vertebrae that bend downward, by which the upper or incumbent vertebrae are articulated with those below. Because these processes go downward, we shall call them the descending processes in our account.
O, O, etc. O is seen on the vertebrae that are placed beneath the ones just mentioned, and marks the vertebral processes [processus articulares superiores] that face upward, by which the upper are articulated to the lower. These we shall rightly call the descending 9 processes.
P, P, etc. P is inscribed on those vertebrae which we previously marked with L, M, and O. It marks vertebral processes [processus spinosi] put forth to the posterior of the body, not unlike a thorn or spike, 10 whence they are called a)/kanqai by the Greeks and spinae by the Latins; from this we call the whole structure of the vertebrae a)/kanqa and spina. In this account, we shall as a rule call these processes the posterior vertebral processes or spines, and shall call the entire backbone by this name more rarely.
Q, Q, etc. You will find Q next to the same vertebrae where we inscribed the last-named letters. Q does not mark part of the vertebra: it identifies the foramen [foramen intervertebrale] on the sides of the vertebrae that transmits the nerves coming out of the dorsal medulla. It will be explained fully how this foramen varies in the bones of the spine in the description of each. 11
R, R, etc. Cartilaginous ligament [discus intervertebralis] intervening between the bodies of the vertebrae. Galen contends this is pure cartilage, contrary to the opinions of the ancients. But how rightly he does so we will show in the twenty-seventh chapter 12 of the second Book, and we will provide an illustration there that is not useless for this account, representing some bodies of vertebrae that show this cartilaginous ligament, epiphyses of the vertebral bodies, and the cartilage that comes between the body of the vertebra and its epiphysis (as these are in children).

Nature’s purpose in the creation of the spine: to provide support
Nature, the parent of all things, fashioned man’s spine like a sort of keel and foundation. 13 For it is by means of the spine that we are able to walk upright and stand erect. Yet she did not give mankind a spine for this purpose alone, but just as she is accustomed elsewhere in the construction of a single member to turn it at the same time to various uses, so no less here she showed its purposeful construction. 14

To provide a path for the dorsal medulla, and at the same time be flexible
First, she carved out a foramen [foramen vertebrale] (visible in the figures of the next three chapters) in all the vertebrae near the posterior region of their bodies, preparing a suitable path of descent through them for the dorsal medulla [medulla spinalis]. Second, she did not make the whole spine from an uncompounded and simple bone,

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though this would have sufficed for stability and a safe place for the dorsal medulla because it would be able neither to be dislocated nor slip out of place or be twisted unless it were so variously jointed. 15 But if the Maker of things had applied his mind so much to stubborn resistence and not set his sight on any prior or more worthy objective in the structure of the body’s organs, he would surely have created nothing other than a quite uncompounded and simple spine. Indeed, if one constructs an animal of stone or wood, one fashions a spine in no other way than from a single and continuous part. But for a human who will bend his spine downward or make it erect, it was not better that it all be formed from a single bone; indeed, since it is necessary for a person to be set into many different motions by means of the spine, it was better that it be composed of many bones, no matter how much for this reason it is made more vulnerable to injuries. 16

The reason for the large number of bones
Now why the spine is made not from two or three bones as long as the humerus in the arm with the ulna and the radius, or the femur in the leg with the tibia and fibula, but from thirty-four bones 17 differently articulated with each other, must be considered at this point with a view to the paramount component of the whole spine, now that our account is begun. This component is the dorsal medulla [medulla spinalis] (three figs. at the beginning of ch. 11, Bk. 4), which we shall endeavor to show, when we explain the series of nerves in Book Four, is like a brain for the parts located beneath the head. Because it was necessary that like the brain this be sheltered by a hard protective covering that would readily ward off injuries, the spine needed to be carved altogether like a keel placed beneath the human body, and at the same time a pathway, an extremely safe fortification, and as the Greeks say a su/rigc i(era/ 18 needed to be made for the medulla itself. Its nature resembles that of the brain, and the ills that beset a person when it is affected are comparable to those which we daily see occur when the brain is damaged. For the movements and sensation of all parts below the damaged vertebra are impaired. Galen attests that this is generally known. The divine Hippocrates instructs us in his book De articulis that if several contiguous vertebrae are displaced, it is serious, but if one moves out of alignment with the others, it is fatal; this is by no means well known to all. Hippocrates instructs us about the cause of a symptom: if several vertebrae are displaced at once, so that each moves slightly and is out of place, then there occurs a curved or not severe distortion of the dorsal medulla. If, though (he says), one of the vertebrae is displaced from its position, the dorsal medulla is diverted for a short distance and is damaged; the vertebra that moved will compress it if it does not also break it. 19 Since, therefore, the dorsal medulla cannot tolerate an angular bending that is sudden and sharp, the spine cannot be moved by means of large, loose joints having considerable movement without suffering damage. Therefore it was better for the spine to be built up of many small bones, each of which contributes to movement.

The unequal size of the spinal bones and spinal cavity 20
Moreover, the size of these bones is not the same, nor is the foramen carrying the dorsal medulla carved out in equal size for all of them. In the interest of coordination it was better that the lesser ones be made always the higher; the one which is now supported by another should be smaller than the one bearing it. On this principle, the sacrum (G, H; or, in the complete skeletons, M with Q 21 ) was made by Nature the largest of the bones of the spine, and is placed beneath the twenty-four vertebrae as a kind of base, joined to the two largest bones (G and H), which together with it most stabilize the body. The second largest bone of the spine ascending up from the sacrum is the vertebra (F, or number 24) articulated to the sacrum, lying twenty-fourth from the first, the fifth of the lumbar vertebrae. Each of the other vertebrae differs as much in mass from the one below as it does in position. This reduction in size continues up to the head itself, except when a vertebra intervenes that is a little greater 22 than the one beneath; the description of the first vertebra [atlas] of the neck (A or 1) will show that this is not made without great usefulness. This description will explain that it is broader than the other cervical vertebrae for the convenient insertion of the fifth (I, H [musculus obliquus capitis superior] in the 14th table of muscles) and sixth (L, K [m. obliquus capitis inferior] in the same table) muscles that move the head, and the origin of the second muscle that elevates the scapulum (Q [m. levator scapulae] in the 13th table of muscles). In that passage you will hear also that for the sake of articulation the second cervical vertebra [axis] is stronger and larger than the third. Because Nature carved out the vertebrae on the posterior surface of their bodies for no purpose other than to prepare a path for the dorsal medulla (1 in the illustration preceding ch. 11, Bk. 4), it was assuredly necessary for the foramen to match the size of the dorsal medulla. And since the medulla is unequal in individual vertebrae and largest in the first ones (for it is gradually diminished and reduced by nerves put forth from it), the foramen of the upper vertebrae is rightly greater than that of the lower. Since, moreover, the upper vertebrae needed to be carved out with a large foramen and at the same time rest upon other vertebrae, it is readily deduced that they must necessarily be made thin at the same time.

Foramina made for putting forth nerves 23
The path in the vertebrae for the dorsal medulla is not the only one carved out: the safest possible passages (Q, Q) [foramen intervertebrale] and foramina are also hollowed out in the human 24 vertebrae for thirty pairs of nerves 25 (three figs. preceding ch. 11, Bk. 4) that originate in the dorsal medulla [medulla spinalis]; I will explain these in the section on nerves. In the separate descriptions of vertebrae, however, some mention of these foramina will often occur, especially as they are not of the same kind or equal number in all the vertebrae.

The spines of the vertebrae 26
Since, therefore, the dorsal medulla is considered like another brain for nearly all the organs that are beneath the head, and the spine is fashioned as a passage for it and a safe fortification, the Maker of things built many other

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marvelous things around the vertebrae: he extended a spine (P, P, P) [processus spinosus] from the middle of their posterior parts like a fence or palisade for the whole backbone, with the intention that it would be broken, crushed, and subjected to any damage before harm could come to any vertebra and the dorsal medulla itself be hurt.

The cartilage growing near the tips of the spines
A cartilage grows on these posterior processes in most vertebrae possessing an epiphysis (F, G in figs. 2 and 3, ch. 17), a suitable defence for what lies beneath, as it cannot be broken or fractured like things that are fragile, friable, and hard, nor severed and bruised like soft and fleshy parts. 27 The size of the individual processes which we said protrude like a spine is somewhat irregular in all the vertebrae; this too is equally the result of Nature’s marvellous foresight. For in those places where any very important part takes for itself the same place as the dorsal medulla, it was by no means just to neglect the priority of this part, nor in places occupied by the medulla alone was it just that long spines be grown. Similarly, it was inexpedient for a long spine to grow out of little vertebrae, or a short one from a large vertebra. So with the best reasoning, since the heart is located in the thorax and the great artery [aorta] lies upon the spine, in these portions of the backbone Nature put forth the longest spines, and shorter ones in other places. The bodies of the lumbar vertebrae are great, and to the inside of them is supported the great artery [aorta abdominalis] and the vena cava (the figs. of Bks. 5 and 6 show what is placed before the anterior of the vertebrae); but the mass of the sacrum is greater and more remarkable, though no particular organ is situated in front of it. It was therefore reasonable that the rear processes [processus spinosi] after the vertebrae of the thorax be grown largest in the loins and shortest in the sacrum. The neck vertebrae, since they are the thinnest of all, were not able at the same time to obtain long processes that were fit for enduring injuries without harm since they are easily broken because of their thinness. 28

The transverse processes 29
Like the processes just mentioned that make a spine and serve the purpose of a bulwark, there are others, namely the transverse processes (M, M), with which the vertebrae are equipped. These are put forth in part as a kind of seat for the muscles that move the back; 30 likewise, the spines also aid quite substantially as origins and insertions of muscles, 31 which is why nearly all processes of bones as a rule bulge or grow out like mountains or hills: this has been previously stated more than once. Muscles lie upon all these vertebral processes, along with the arteries, veins, and nerves brought to them or through them. 32 But there is another, third use of the transverse processes of the thoracic vertebrae in addition to those stated: they provide a fit seat [fovea costalis processus transversi] for the ribs to which they are articulated (figs. 1, 2, 3 in ch. 19).

Articulation of the vertebrae 33
Now because the spine needed to be formed from the vertebrae as a single body which would be at the same time firm, strong, and flexible, Nature deserves great praise for constructing a spine suitable for both (though contrary) uses. All the vertebrae down to the sacrum (except the first two) are safely bound to each other on their anterior portion (R, R) [discus intervertebralis] by large bodies, and on their posterior (N, O) they are fitted together by double joints [articulationes zygapophysiales], where they gain strength from the anterior structure. Thus the vertebrae are not kept from moving because they are not bound together at their bodies and they are kept separate in their posterior by clearly visible joints. For this reason we are readily able to bend forward but not at all backward. 34 For if you force the membraneous ligaments 35 that join the bodies of the vertebrae (R, R), you will break them along with the other cartilaginous ligament [discus intervertebralis] placed between the bodies of the vertebrae and thus connecting them, so that the vertebrae do not differ much from the tissues connected to it. The next Book will deal abundantly with the nature and substance of these ligaments, and all other matters.

That it was more suitable for the spine to bend forward
Now because it was not equally safe for the spine to bend forward and backward (for if so it would have been weak, unstable, and loose), Nature justly selected what is better. For all the tasks of life it is more practical that the spine bend forward; this flexion also brings less harm on the vessels resting on the spine at that point, such as the great artery [aorta] and the vena cava, since they are otherwise extended considerably. Therefore because it was necessary that the spine be precisely confined in its anterior portion, the vertebrae are deservedly jointed more loosely in their posterior part. We shall now add what form these joints take and what remains to be said about individual vertebrae. 36 For there are several differences in the vertebrae, showing the unbelievable skill of Nature throughout. For this reason they must be explained in no perfunctory or hurried way in the four chapters now to follow, of which the first will be dedicated to the vertebrae of the neck or cervix, the second to those of the thorax, the third to those that are in the loins [lumbar], and the fourth to the sacrum and coccyx.

APPENDIX Vesalius’ 1555 version of the Chapter 14 narrative
As we have seen, the 1543 narrative is scarcely more than a condensed translation of Galen’s account of the spine in the twelfth book of De usu partium. For his second edition of the Fabrica, Vesalius extensively recast his text as follows. In this translation we have omitted marginal subject headings and references to the figures.

Nature, the parent of all things, contrived the spine, which is called by the Greeks a/xij and nw/toj, like a kind of keel and fulcrum. It is the means by which we walk upright and stand erect. But Nature did not fashion the spine for this alone: just as often she makes a member elsewhere fit for various uses at the same time, here too she did not forget her purpose. In the bones of the spine, lest they only /p. 72/ sustain and merely steady the body for the common use of the bones, she carved a great foramen [foramen vertebrale] into which to fit a suitable path of descent through the spine for the dorsal medulla [medulla spinalis], called by the Greeks i(era\ su/rigc, as it were a kind of sacred pipe or fistula. This foramen is so carved that because of it anatomists have called the bones of the spine vertebrae, from their resemblance to the pivots, verticulae, with which spindles are weighted. 37 Moreover, Nature did not make up the spine from a single, simple bone, though this would have been good for stability and have made the seat of the dorsal medulla safer from dislocations and sprains. Yet she constructed the spine of several bones for the sake of the several movements which it was necessary for man to make, even though it would thus be more exposed to dislocations. The reason why it is not fashioned from two or three bones as long as the humerus combined with the ulna and radius in the arm, or the femur in the leg combined with the tibia and fibula, but from about thirty-four bones 38 (of which we assign seven to the neck, twelve to the thorax, five to the loins [lumbar], six to the sacrum, and four to the coccyx), is primarily the dorsal medulla. Because this needed to be the origin of thirty pairs of nerves, 39 and because it would be like a brain to the parts located beneath the head, it needed to be protected and kept free from all compression and distortion, lest all the lower parts lose sensation and be deprived of voluntary motion because of any such damage to the dorsal medulla. We learn how readily the dorsal medulla would be bruised or otherwise exposed to the gravest injuries if the spine consisted of only two or three bones, from the angular flexion of the elbow or knee, and from the long, loose motion of any joint provided with bone movement. Thus is was necessary that the spine be composed of so many small bones placed next each other in succession and providing some gradual motion at one time to allow the spine to be moved, and at the same time make no motion in a very sharp angle, which would be extremely harmful to the dorsal medulla because of compression. For this reason Nature in her wisdom has always established in all animals, birds as well as fishes, reptiles, and quadrupeds, a series of such small bones large enough to be a part of the neck and all the rest of the body which encloses the dorsal medulla and needs flexibility. For she is sparing in the number of bones, and still more in their loose composition, when the dorsal medulla is preserved anywhere that did not have to be moved. This is beautifully shown by tortoises, which have vertebrae only in the neck and near the beginning of the tail and have a long path in their rigid shell that contains their dorsal medulla and has no vertebrae. Besides the sacrum in humans, birds also attest to this, since their thorax, unlike their neck, consists of few vertebrae: their sacrum is as long, and is composed of a single or simple bone. It is marvellous how Nature designed the bones of the spine for all animals to be useful for them; as we said above about the relation and size of the bones when we perceive that the bones of swimming and snakelike animals quickly diminish in stages from the head to the tail and consider that the spines of walking animals have the largest bone at that point in the body's trunk which is strengthened for the femurs or is otherwise close to them. From this bone, as from a base and broad surface on which they are sustained, the other bones ascend to the head and gradually become smaller in the same way as the vertebrae of fish and reptiles become narrower as they extend downward from the base and largest bone from which they hang (as it were) toward the tail or whatever is analogous to it. Thus in man the largest of the bones of the spine is the sacrum, which is joined [articulatio sacro-iliaca] by its sides [pars lateralis, facies auricularis] to the bones [os ilii] which together with it neatly strengthen the body and receive the joints of the femurs [articulatio coxae] and the coccyx [art. sacrococcygea]. We do not say that the sacrum is large only because it is constructed of its own six bones or vertebrae 40 and is named as if it were a single and simple bone, but also because the largest [vertebra sacralis I] of its six bones and the one [vertebra sacralis II] beneath it are larger than the individual bones of the spine above them, and it must be set down as the supreme in mass and like a base. Of the twenty-four vertebrae resting upon the sacrum, the largest [vertebra lumbalis V] is that which is nearest to it and jointed [articulatio lumbosacralis] to it; the rest are smaller in proportion to their position away from it. This reduction continues as far as the head itself, except when a vertebra comes between that is a little larger than the one beneath; our account of the first cervical vertebra [atlas], which will explain that it is wider than the other vertebrae of the neck, will show that this does not occur without great reason, namely the convenient insertion of the fifth and sixth muscles [m. obliquus capitis superior et m. obliquus capitis inferior] that move the head and the origin of the second of the muscles [m. levator scapulae] that raise the scapula. Similarly, the second cervical vertebra [axis] will be shown to be rather stronger and thicker than those beneath it because of its joints. Now the six bones of which the sacrum is constructed and the four ossicles of which the coccyx is composed are so arranged in magnitude that they continually shrink from a broad base, from the first and second bone of the sacrum, as if to a point. Though the size of the spinal bones varies and they do not gradually grow smaller from the head down, the foramen carved for the dorsal medulla does not correspond to the size of the bones but to that of the dorsal medulla: because this is gradually reduced by the exit of nerves, larger foramina will naturally present themselves in the upper bones than in the lower. From this path for the dorsal medulla in the bones of the spine, a route lies open for all the nerves originating from it, running through foramina so carved between the vertebrae that two bones always contribute something toward the formation of a single foramen [foramen intervertebrale], though not in the same place on every side. For although very many vertebrae have these foramina in their sides, they are in the front and back in the sacrum and upper neck bones. This is particularly true (as we shall state where it occurs) at joints of vertebrae with each other and with other bones that are conterminous with them. Nature, having a plan for the strength of the whole spine as well as its motions, built with considerable care. For on the broadest surfaces of the bones, which we call the bodies of the vertebrae, she joined them to each other on bases as wide as if they were a single bone and a unified set rather than on smooth and slippery surfaces, as we see it is done elsewhere in almost all joints; instead she roughened the bases and broad surfaces, and put a cartilagineous ligament [discus intervertebralis] between them which is attached to those surfaces and very strongly binds together the bodies of the vertebrae. Since it is quite thick and possesses the quality of softer cartilage and for this reason can be compressed and reduced by pressure and any force of muscles on attached bones, and again when it is not squeezed it quickly springs back to its original thickness, 41 it is certainly the reason why the bodies of the vertebrae that are held in by it can move in ways the cartilaginous ligament cannot; these tissues are smooth, rounder, and rather more oblique than inclined in any way into a right angle. Furthermore, in addition to this structure which is rare and common to almost no bones except those of the spine, which is anterior to the foramen that carries the dorsal medulla and occupies the inside parts of the whole vertebral body, Nature constructed a single joint [articulationes zygapophysiales] on each side next to the posterior edge of the foramen, which would have smooth and slippery surfaces like all the other joints in the body. From the higher surface of the vertebrae two processes are extended upward, which we call for this reason the ascending vertebrae [processus articulares superiores]; and from the lower surface two others are thrust downward, called therefore the descending processes [processus articulares inferiores]. By these processes /p. 74/ the vertebrae are articulated on this lower surface, but not everywhere with equal concavities and tuberosities or with the same ingress, as will soon be explained in the chapters that follow. There you will learn that the first cervical vertebra, which should have been turned above the second by its own motion, varies from the other vertebrae in these three structures. 42 And because the bones of the sacrum did not need to be moved as the other vertebrae are, you will understand that they are everywhere attached to each other and fused. I shall write that the structure of ossicles [vertebrae coccygeae I-IV] belonging to the coccyx (which is simple and single) 43 resembles that by which the bodies of the vertebrae are linked by cartilaginous ligaments. Also, just as Nature provided for the motions of the spinal bones as much as possible by powerful structures that were resistant to dislocations (not to mention the remaining series of ligaments), so also between these structures for the sake of the descending dorsal medulla, no doubt to protect it better from outside impacts, other processes still more conspicuous than the ones just mentioned are put forth by the bones that enclose the medulla. From their posterior surface, long processes grow to the rear which we call spines, calling the whole structure of the backbone a spine after them. In addition, another process is extended on each side from the lateral and transverse sides which we call the transverse process, having a cartilage on its tip like the posterior processes for the same purpose we know cartilage grows on the ends of bones where another bone is not connected. 44 These processes are created not only to act as a fortification for the dorsal medulla and the parts beneath, but they are also supremely suited to put out origins of numerous muscles and receive insertions of the same; the transverse processes of the thoracic vertebrae are convenient besides for articulation of the ribs [articulatio costotransversaria]. Similarly, the transverse processes [pars lateralis] of the sacrum serve the structure which this bone makes with the bones [os ilii] laterally attached to it. Why the first vertebra of the neck is alone lacking a spine, and why the spines of the neck vertebrae and their transverse processes are forked; why the thoracic vertebrae (especially the upper ones) put out very long spines while the lumbar vertebrae and the bones of the sacrum do the opposite, and how all these processes vary in direction and shape; what features pertain to each separate appendix, what form each vertebral body takes, what special appendices they have above and below, I shall endeavor to set down in the four chapters that follow, devoting one chapter to each of the four major portions 45 of the spine. For a short and concise account cannot contain the many rare and special features Nature achieved in the construction of the spinal bones.

Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them]