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

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] | Chapter 14 On the Spine and its Various Bones