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 16 On the Vertebrae of the Thorax

[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.

page 72

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. 13
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

page 73

with all possible diligence, explaining all the parts of the thoracic vertebrae in order, so that one may more quickly discover in what respects they fight with each other. For there is no small diversity in the vertebrae of the thorax.

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 articulated.
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

page 74

processes (H and I in figures 1, 2, 3, 4), the thoracic vertebrae also vary from one to another, but not so much as Galen stated in the thirteenth book of De usu partium where he deprived the tenth vertebra and the two beneath it of transverse processes. 26 For there is a transverse process on each side of all vertebrae of the thorax; its size scarcely varies in the nine upper vertebrae, 27 while in the tenth the transverse processes swell out less than in the higher vertebrae, as the tenth rib attached to it is quite small and a false rib. The transverse processes of the eleventh vertebra are still smaller than in the tenth, and smaller yet in the twelfth, no doubt because the need for these processes is not so great as in the higher vertebrae. 28 All of these others have ribs articulated to them, for the sake of which the thoracic vertebrae have the strongest and thickest transverse processes. But ribs are not articulated to the transverse processes of the twelfth and eleventh vertebrae, for the two lowest ribs of each side are joined by a single articulation only to the body of the vertebrae, while the rest are jointed to the bodies of the vertebrae and the tips of the transverse processes. At the tips (K in fig. 1, and c, b in fig. 3, ch. 19) of the transverse processes of the upper nine thoracic vertebrae are seen depressions [fovea costalis processus transversi] coated with cartilage, to which the capitulum of the rib 29 (M in fig. 4, ch. 19) is articulated. In the transverse processes of the tenth vertebra, no such depressions are seen, or sometimes obscure ones, and in the processes of the lowest two none whatever occur. The depressions carved in the tips of the transverse processes are all located in the anterior portion, but some occupy the upper and others more the medial region. 30 The depressions of the transverse processes of the first vertebra face downward, of the ninth upward; of the middle, in between. Galen seems not to have noticed this: while explaining the rib joints, he judges that all such depressions face downward and are carved in the lower surface of the tip of the transverse process. 31 He should in no way have deprived the tenth thoracic vertebra and the two beneath it of their transverse processes on the grounds that they would inhibit the lateral motion of the entire backbone. 32 For if Nature had wished transverse processes to be absent from these vertebrae for the sake of that motion, she would not have had to deprive the vertebrae below the tenth (which Galen stated is supported above and below 33 ) of their transverse processes any more than those above. If the transverse processes of the lower vertebrae were to obstruct lateral motion, surely the upper ones would have resisted this motion no less than the lower. Just as the portion of the backbone below a vertebra that is received above and below is moved upward in that motion, so it is also necessary for the portion lying above it to be borne downward, if the backbone needs to be moved laterally as in a semicircle, where the midpoint of the semicircle’s circumference is rightly thought to be that vertebra which is supported above and below, whichever one that might be. But what is the use of lingering on this talk which is so difficult to understand because of the vertebra that is supported on both ends? The tenth and the two thoracic vertebrae below it have transverse processes as prominent as suits their function in the origin and insertion of muscles. Indeed Galen, who is to some degree consistent, stated in many places that all the ribs are articulated to two internodes, one in the body of the vertebra and the other on the transverse process. 34 If this were the case (which it assuredly is not), would not also the tenth thoracic vertebra and the two below it necessarily have transverse processes? We shall state in what direction the processes are extended, whether upward or downward, when we add the spines of the thoracic vertebrae to our account.

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

page 75

that triangular look as perfectly because the two upper surfaces are rather broad. The third or lower surface is narrow and not very depressed, but noticeably rough and uneven. The point of this spine is wide and blunt, not narrow and sharp like the spines of the higher vertebrae. The spine of the eleventh vertebra (R in fig. 3) extends still less than that of the tenth, is more depressed on both sides, and (if you look above and below it) 37 more broadly shaped. Its lower surface swells noticeably into a line and is no longer depressed 38 but rough and compact; the point of this spine is quite blunt and thick. The spine of the twelfth (S in fig. 4) differs still more from those of the upper vertebrae, substantially resembling the spines of the lumbar vertebrae (C, D, E, F, G in fig. 2, ch. 17), which are quite depressed on each side and, if you look at the top and bottom, quite broad and bulky. And just as the spine does not have the same shape in all the vertebrae, so too the spines differ from each other in their course (see the fig. in ch. 14 and skeletons 2 and 3).

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

page 76

and in the former the tenth thoracic, as he observed in apes and dogs. 49 But I have never seen the tenth received on both sides in man: it is most often the twelfth. Sometimes, when I have found a sacrum consisting of only five bones, I discovered the eleventh received on both sides, and at Bologna we assembled the bones of a French priest 50 whose first lumbar vertebra was received on both sides, and it had its transverse 51 processes articulated to itself just as the twelfth thoracic vertebra articulates to the twelfth ribs. Since, then, the twelfth thoracic appears most often to be received on both sides, let us base our account on this. Ascending processes (T, V in fig. 1) protrude from eleven thoracic vertebrae, and in the outer or posterior surface (X, Y in figs. 2 and 3) they are coated with a cartilage [c. articularis] in a noteworthy roundish area. The convexity of these processes [p. articularis superior] is so slight and flat that you can scarcely tell whether it should be considered a depression or a swelling. 52 The descending processes [p. articularis inferior] also possess a large depression [fovea costalis inferior] on their inner or anterior surface (c in figure 1) where they face the foramen cut out for the dorsal medulla, also more or less round 53 and coated with cartilage, corresponding exactly to the convexity just mentioned. These depressions and swellings differ from the depressions and swellings of the neck vertebrae only in their direction. The depressions and swellings of the neck vertebrae extend obliquely upward from the anterior, or obliquely downward from the other direction. It makes no difference whether you say they run upward or downward as long as you understand their obliquity and compare their position with that of the depressions and swellings of the thoracic vertebrae, which are more or less vertical as the structure of the thoracic vertebrae is stiffer and more resistant to movement. Since therefore the ascending processes of the thoracic vertebrae, like those of the neck, protrude on their posterior surface while the descending processes are hollowed out on their inner surface, the ascending processes of the lower vertebra naturally fit up into the descending processes of the upper vertebra, and the lower vertebra is taken in by the upper.

The course of the processes of the neck vertebrae is measured from a to b, of the thoracic from c to d.

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.

page 77

But now it will be preferable to devote a special chapter to those vertebrae as well, and to describe them more fully there.

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]