[Figures of Chapter 16]
Key to the Four Present Figures and Their Letters
We have drawn here those of the twelve thoracic vertebrae which we thought sufficient to illustrate their description. The entire series of dorsal vertebrae [vertebrae thoracicae] is presented in the figure preceding the fourteenth chapter and again in the three representing the entire structure of the bones at the end of this book. The vertebrae of the thorax, along with the ribs which are articulated to them, are separately illustrated in the two first figures at the beginning of the nineteenth chapter. 1 The first figure of this chapter shows one of the middle thoracic vertebrae [vertebra thoracica V] in its anterior part; about ten upper thoracic vertebrae resemble it. 2
The second presents the same vertebra as is shown in the first, seen in its posterior face.
In the third is displayed the eleventh thoracic vertebra in its posterior face.
In the fourth we have illustrated the twelfth thoracic vertebra, also in its posterior face.
|A 1 , 2 , 3 , 4||In all the figures, A marks the superior part of the body [corpus vertebrae], by which it is joined to the vertebra above it. 3 Because the lower part closely matches the upper, it would have been unnecessary to draw a thoracic vertebra in its inferior aspect. F placed in the third figure marks the upper epiphysis 4 of the vertebral body, which generally remains after boiling and cleaning of the bones. 5|
|B 1||Middle of the depression [fovea costalis superior corporis vertebrae] which we shall state is common to two vertebral bodies, and to which the base of the rib [facies articularis capitis costae] is articulated.|
|C 1||Part of a depression [fovea costalis inferior] of this kind is carved in the lower surface of the vertebral body; it is smaller than the part marked B to the same degree as the common depression made for articulation of the rib belongs more to the vertebra below than to the one above.|
|D 3||Depression [fovea costalis] in the eleventh vertebra to which the eleventh rib of the right side is articulated.|
|E 4||Depression [fovea costalis] in the twelfth vertebra to which the twelfth rib of the right side is fitted.|
|F 4||A rough, deep depression [pediculus arcus vertebrae] from which comes the ligament [l. costotransversarium] connecting the twelfth rib to its vertebra.|
|G 2 , 3 , 4||Greater foramen 6 [f. vasculare] cut in the posterior surface of the vertebral body facing the dorsal medulla.|
|H and I 1 , 2 , 3 , 4||Transverse processes of the thoracic vertebrae.|
|K 1||Depression [fovea costalis processus transversi] visible in the tip of the transverse process, to which a rib is articulated.|
|L 1 , 2||Portion of the transverse process which we shall state is gibbous.|
|M 1||Concave portion of the transverse process. 7 Because in the remaining three figures, which illustrate the posterior aspect of the vertebrae, the transverse processes are shown to be brought slightly downward, a large portion of the upper part is shown and the eye is not directed to the middle of the lower surface.|
|N, O, P 1 , 2||Spine or posterior process; in the second figure the upper surface [lamina arcus vertebrae] of the spine is illustrated, where N, O, and P mark three lines that together make a triangle. The interval between N and O is one upper surface, and the other interval, between N and P, is the other surface. The first figure marks the third surface of this process which is the lower, between O and P. The unshaded area seen next to N in the first figure is a portion of one of the upper surfaces.|
|Q 1||Line projecting in the third surface; it is rough and uneven.|
|R 3||Spine of the eleventh thoracic vertebra.|
|S 4||Spine of the twelfth thoracic vertebra.|
|T, V 1||Anterior surface of the ascending processes [p. articularis superior] of the thoracic vertebrae above the twelfth.|
|X, Y 2 , 3||Posterior surface of the ascending processes [p. articularis superior] of the thoracic vertebrae, where these processes swell out and are coated with cartilage.|
|a b 2 , 3||Outer surface of the descending processes [p. articularis inferior] of thoracic vertebrae.|
|c 1||Here is seen the anterior surface [fovea] of the right descending process [p. articularis inferior], which is concave and covered with cartilage; it receives the tubercule of the ascending process of the vertebra below. 8|
|e, f 4||Ascending processes of the twelfth thoracic vertebra, which go up into the eleventh vertebra.|
|g, h 4||Descending processes of the twelfth thoracic vertebra, which are articulated into the depressions of the ascending processes of the first lumbar vertebra.|
There are most often twelve thoracic vertebrae.
The vertebrae of the thorax are numbered twelve (C-D in the fig. in ch. 14; K to L in the skeletons; see also the whole structure 9 of vertebrae in figs. 1 and 2, ch. 19), though sometimes, albeit rarely, one is missing or there is an extra. But it is found that one is missing more rarely than one is in excess. 10 At Padua I found two bodies 11 with thirteen thoracic vertebrae, but so far I have never seen only eleven vertebrae. The number of cervical and lumbar vertebrae is not varied as often as that of the thorax. 12 Furthermore, even though thoracic vertebrae are made up of a constant number, they do not display the same type of articulation in all.
A vertebra is supported above and below by others.
For although there is one of the thoracic vertebrae that goes up into the vertebra placed above it with its ascending processes and likewise into the one below with its descending processes, or is taken in by two vertebrae, it is not always the same one (assuming there are only twelve thoracic vertebrae), since now the eleventh, now the twelfth, or some other is sometimes joined to the neighboring vertebrae by this type of joint. To make it easy for one to understand exactly what this vertebra is and how it is articulated to the others is a very difficult task here to describe but quite easy for me to demonstrate; I shall attempt this
Diversity in the bodies of thoracic vertebrae.
First, the bodies of the thoracic vertebrae vary in size to the degree one is closer to the neck than the other (the first of the figures showing all the bones and the fig. for ch. 14 show this variation of articulation and bulk). The body of the first thoracic vertebra is thus quite smaller than the twelfth. Next, the body of the first, on its superior surface where it is joined to the seventh cervical vertebra, is not entirely flat but swells slightly at each side and subtly imitates the bodies of the cervical vertebrae (h, k, q in fig. 9, ch. 15); but the lower part of this body has a flat surface like the upper and lower surfaces of the bodies of all thoracic vertebrae (A in figs. 1, 2, 3). No lower portion of the body in the thoracic vertebrae is in fact extended even the least bit in a long downward slope or ends in a depression of the body of the next vertebra, as do the cervical vertebrae (r in fig. 8 and z in fig. 9, ch. 15). Yet Galen attests otherwise 14 , attributing more or less the same articulation to the thoracic vertebrae as we have shown in the preceding chapter that the bodies of the cervical vertebrae construct. Moreover, the bodies of the first and second thoracic vertebrae do not protrude forward with a round or curving anterior shape as much as the bodies of the other thoracic vertebrae, which much more resemble a circle or the letter C than the highest vertebrae, and protrude farther into the thoracic cavity. The two upper vertebrae of the thorax, like the cervical vertebrae, are depressed in their anterior surface and are much broader (so to speak) than deeper, and conform to the bulge of a half parenthesis, “(” , rather than a C. This special feature occurs in them not only to provide a loose articulation fit for motion but also for the muscles that flex the neck (A and B in the 8th table of muscles) [m. longus capitis]. For those muscles are so laid out upon both sides of the bodies of the first thoracic and all the cervical vertebrae that it is clear the vertebrae are compressed by them. But the remaining vertebral bodies have no such muscles attached or lying upon them. 15 It also happens to all the thoracic vertebrae alike that they have a depression on each side [fovea costalis superior corporis vertebrae] to which the capitula of the ribs [facies articularis superior capitis costae] are articulated.
Diversity in the depressions to which the ribs are
But as the capitula [capita costae] of the ribs vary in that joint, so all the vertebrae do not possess at all the same depressions. Where the first thoracic is joined to the second, the second to the third, and so in succession to the joint of the ninth with the tenth, a certain depression [fovea costalis superior et inferior] (B and C in fig. 1, but more clearly in X and d in fig. 3, ch. 19) is incised on both sides next to the foramina [f. intervertebrale] for the nerves [nn. spinales] (Q, Q in fig. 1, ch. 14). This depression is common to the bodies of both vertebral bodies that are connected to each other, and is incised partly into the body of the vertebra above and partly into the one below, though its larger portion extends more to the lower vertebra. 16 This depression is coated with cartilage, 17 and is formed nearly in the shape of an obtuse angle, much as the capitulum [caput costae] of the ribs (L in fig. 4, ch. 19) entering this depression bulges in the manner of an obtuse angle, as we shall show in our discussion of the ribs. The first thoracic vertebra has the following property along with the eleventh and twelfth: a special depression on each side not shared with other vertebrae, 18 carved in its body alone (look for these in E and F, fig. 4). 19 Near the upper surface of the first thoracic vertebra, a round, quite deep depression [fovea costalis] is hollowed out on each side and lined with cartilage; to this is articulated the base [collum costae] of the first thoracic rib by means of a round capitulum. At the bottom of this depression, another quite deep one is seen, rough and uneven, filled with certain foramina and not covered with cartilage; from this comes an extremely strong ligament [l. costotransversarium] that powerfully binds the rib into its socket. Similarly, the depression 20 carved in the twelfth vertebra for the twelfth rib possesses another deep depression in its lower surface, also rough, but less so than the just mentioned depression of the first vertebra; this one is hollowed out for the ligament [l. costotransversarium laterale] attaching the twelfth rib more firmly to the vertebra.
Variety based upon the substance of the vertebrae
Finally, a certain variety accrues to the bodies of thoracic vertebrae also with respect to their substance; for the larger and bulkier the body of each vertebra the less solid it is, but porous and distinguished with a random series of many foramina [ff. vascularia] in various shapes and sizes, through which veins and arteries enter to nourish the vertebral bodies. For unless twigs of the vessels make their way into the substance of the thick bones, it is impossible for the middle and inmost substance that is remotest from the surface to draw in nourishment (since it is so distant). Among the foramina of this kind, none are easier to see than the ones in the posterior surface of the vertebral bodies that faces the dorsal medulla (G in figs. 2, 3, 4). Here in most vertebrae a single special foramen is seen, large in proportion to the mass of the vertebra, rough, and ending in many small foramina [canalis nutriens]. 21 Though Galen appears to have ascribed such foramina only to the lumbar vertebrae, 22 if one carefully inspects each one he will see that the first lumbar, the twelfth and eleventh thoracic, and some vertebrae above them put forth these foramina, more conspicuous, more numerous, and deeper in proportion to the magnitude of the vertebrae, and that the body of these vertebrae is more porous than all the rest. This is because they are large vertebrae, do not have the trunk of the hollow vein (z to o in the fig. preceding ch. 6, Bk. 3) 23 resting on them, 24 and are wound only with the branches of the unpaired vein (F and later G in the same fig.). 25
Variety based on the transverse processes
In the transverse
Varieties of the spine
Nature granted to all the thoracic vertebrae a spine that is single over its entire course and not at all forked (c and ϖ in fig. 8, ch. 15). The shape of this spine does not look the same in all vertebrae. The nine upper vertebrae put forth the longest spines (N, O, P in figures 1 and 2), not very broad but narrowing gradually to a point from a broad base and resembling a triangle just as if they consisted of a triangular pyramid. For on their upper surface they present a straight, sharp line extending longitudinally (N in figure 2); they have a similar line along each side next to their lower surface (O and P in figures 1 and 2), so that the three long, sharp lines of a single spine form three surfaces, two of which (from O to N and from N to P in figure 2) constitute the upper portion of the spine 35 facing the vertebra above; there is one of these on each side. The third surface (between O and P in figure 1) is the lower portion [Q], overhanging the spine of the vertebra beneath. These three surfaces in the same spine are observed in the nine superior vertebrae, more or less identical and equally broad. Two of their surfaces are quite smooth, but the third, lower one is rough, and divided by a kind of line (Q in fig. 1) running along its longitude. From this line on the third surface comes a ligament [ll. interspinalia] that is inserted in the line common to the two surfaces; binding the spines to each other and filling the interval between them, it separates the right muscles of the spine from the left, corresponding to the ligament [membrana interossea] that I will explain lies between the ulna and the radius (a between E and I in fig. 1, ch. 1, Bk. 2) and between the tibia and the fibula 36 (S, T, V in the 7th table of muscles). Sometimes the upper surfaces appear broader than the lower one, and the spines themselves are more laterally depressed (as is observed in quadrupeds). The tenth thoracic vertebra puts forth a spine that is not as prominent as the upper ones, and does not present
The course of the spines
The spines of the nine upper thoracic vertebrae, like those of the neck, run clearly downward, heading from top to bottom. The spine of the tenth thoracic vertebra droops downward less than those above it, and is borne more straight back. The spine of the eleventh is more elevated, and the spine of the twelfth even more so. But none of these is so elevated that its point does not always tend more downward than upward; this applies also to the spines of all lumbar vertebrae, which face downward more then upward. This is to be understood in the human backbone; in dogs, apes, hares, and nearly all other quadrupeds the case is quite otherwise, squaring nicely with the views of Galen. 39 In these animals, the spine of the tenth thoracic vertebra runs neither downward nor upward, 40 and the two which lie immediately below the tenth have a spine whose tip faces obscurely upward, while the remaining vertebrae coming after these put out spines that extend upward from below. Quite otherwise, assuredly, the human, in whom no one will rightly claim that even a single vertebral spine inclines more upward than down. 41
The course of the transverse processes
The transverse processes of the neck vertebrae, like the nine upper thoracic, should in Galen’s view extend at a declining angle from the top down; but this angle is so obscure and slight as would scarcely seem worth mentioning. Yet if you have considered the transverse processes of the neck vertebrae in a more than perfunctory way, you will say that they face downward in their outward or posterior side (8, 10 in fig. 8, x in fig 10, ch. 15), while on their inward or anterior side (z in fig. 10, ch. 15), which is broader than the posterior, they tend upward. The transverse processes of the nine upper thoracic vertebrae, on the other hand, have their entire bodies carried more backward and upward than downward. Their upper part (L in fig. 1 and 2) is convex, the lower (M in fig. 1) concave and somewhat hollowed out, as if in this way the processes might suggest the appearance of a downward inclination. The transverse processes of the twelfth thoracic not only incline upward but are also brought backward to an unusual degree, just as the processes of the eleventh and tenth face slightly upward. The transverse processes of the lumbar vertebrae (H in figs. 1, 2, 3, ch. 7) are quite obscurely brought upward, though the vertebra joined to the sacrum is a little more clearly seen to bring its processes upward. In dogs, 42 the transverse processes of the neck vertebrae quite conspicuously and clearly turn downward, while the processes of the thoracic vertebrae are either not turned downward or only slightly. The processes of the lumbar vertebrae slant markedly upward, 43 agreeing exactly with Galen’s descriptions 44 except for the number of vertebrae. For dogs and caudate monkeys have more lumbar vertebrae than humans, 45 who also as a rule have one less thoracic vertebra than dogs. This is the way the transverse and posterior processes of the thoracic vertebrae are constituted; those which we call ascending and descending (N, O in the fig. for ch. 14) are arranged in a series as follows.
The difference between ascending and descending processes, and their
system of articulation
The system of articulation of all vertebrae above the sacrum, accomplished by the processes just mentioned, is double: either the vertebra beneath goes up into the one above and is received by it, or the one beneath receives the one above in its depressions. Thus every vertebra, with only two exceptions, receives on one end and is received on the other. The first cervical vertebra receives on its upper and lower sides: on its upper [facies articularis superior] it receives the capitula [condylus occipitalis] of the occipital bone (N in fig. 2, ch. 15 receives B in fig. 1), and on its lower [facies articularis inferior] it receives the second cervical vertebra (Y in fig. 4, ch. 15 receives c [facies articularis superior] in fig. 5). 46 The twelfth thoracic (unless there is an extra vertebra) is received on both sides and receives none (D in the figure for chapter 14, and next to the 12th rib in the third skeletal figure). All the vertebrae above it as far as the first cervical are joined by the first type of articulation [processus articularis]: the upper vertebra always receives the lower, as the tenth thoracic receives the eleventh. 47 The vertebrae beneath the one which is received on both sides receive the vertebra above them on their upper surface, and on their lower enter into the vertebra beneath; this is the way the first lumbar vertebra is received by the second. 48 The thoracic vertebrae above the one received on either side have the same type of articulation in ascending and descending processes as the neck vertebrae (b in fig. 7, ch. 15, then d in fig. 9 and b, d in fig. 11). According to Galen in De ossibus, these are the nine upper thoracic vertebrae; or elsewhere, in De usu partium, the ten upper thoracic, for in the latter he says the eleventh
How the lumbar vertebrae are articulated with each other
The lumbar vertebrae are joined according to a different system. Their ascending processes [p. articularis superior] (K, L, and M in fig. 2, ch. 17) have an elongated and rather deep 54 depression [fovea] on the inner side where they face each other. The descending processes [p. articularis inferior] protrude with a long 55 capitulum on their outer side (but somewhat toward the anterior); this fits into the depression of the lower vertebra’s ascending process. Thus in the lumbar vertebrae the lower vertebra admits the capitula of the one above in its depressions, unlike the neck and thorax, where the upper vertebra receives the projections 56 of the lower one into its depressions. The twelfth thoracic vertebra has ascending processes (e, f in fig. 4) like those of the cervical and thoracic vertebrae 57 which we have said protrude on the posterior surface. Therefore the twelfth goes up into the descending processes of the eleventh thoracic with its ascending processes, and is received by the eleventh. The descending processes of the twelfth (g, h in fig. 4) also protrude like the descending processes of the lumbar vertebrae, and these enter the depressions of the ascending processes of the first lumbar vertebra. Since it receives the twelfth, what could be easier to comprehend than that the twelfth is received above and below? 58
Why it was fitting that one vertebra be received on both sides in the
middle of the spine
But at the same time it does not make much difference whether the twelfth or the eleventh or some other is received on both sides, so long as we do not overlook the signal craft of Nature, which fashioned a vertebra in the midst of the back, stable and supported on both ends just as we see builders place one stone between two others in vaulted and arched buildings which is supported on each side though it supports no stone itself, while all the others support one stone and are received and supported by another. 59 So that the spine might be moved in the ways assigned it, it is necessary that this vertebra supported on both sides be supported without moving while all the others retire slightly from it and from each other; for as it is unmoved when we flex the back, we draw the upper vertebrae downward and bend the lower ones somewhat upward. 60 In extension, we move the vertebrae back with an opposite motion, since the motions of the back 61 are carried out with a curving but not quite angular figure. You will readily see how little this agrees with the views of Galen in the thirteenth book of De usu partium if you compare the passages. 62 We shall explain the motions of the back together with its muscles, until now poorly understood, in the second book. 63 But now if we go back to the thoracic vertebrae, between the ascending and descending process on either side 64 rough places are plainly to be observed (around G in figs. 2, 3, 4) and irregularly protruding small processes, prepared so that strong ligaments 65 may start from here, more robustly and firmly binding the thoracic vertebrae together the more obscurely it was useful for the thoracic vertebrae to be moved than the cervical.
Number of processes of the thoracic vertebrae
Since these things are so, all the thoracic vertebrae have seven processes: two transverse (H, I in figs. 1-4), two ascending (T, V in fig. 1, X, Y in figs. 2 and 3), two descending (a, b in figs. 2 and 3), and one posterior process or spine (N, O, P in figs. 1 and 2). 66 If the eleventh or some higher vertebra is supported on both ends, the twelfth or all the vertebrae below the one supported on both ends would have two extra processes, since each of the ascending processes would be counted as two on account of the depression [fovea] carved in them. This depression (in fig. 2 ch. 17 the depression is labeled K, the swelling M, L) 67 was thought by some ancient authors to be so pronounced that they seem to have counted each ascending process of the lumbar vertebrae as two.