Key to the seven figures of the nineteenth chapter
Since the following figure legend will refer to all seven of the figures that precede it, we shall as usual add a note for the several numbers 2 so you may understand more easily to which of the figures the letters refer.
|1, 2, 3, 4, 5, etc.[ 1 , 2 ]||In the first and second figure, the twelve ribs [costae] of the thorax are indicated by this number. Of these, the seven upper ribs are articulated to the pectoral bone [sternum], but not the five lower. The numbering of the thoracic vertebrae is evident from the marked ribs even without the help of markings, if you observe that one rib on each side is articulated with a single vertebra.|
|A, A 1 , 3||Whatever part of the ribs runs from the vertebrae to this point [corpus costae] is entirely osseous; here the ribs begin reverting 3 into cartilage [cartilago costalis]. The legend for the remaining markings will be placed below the figures.|
FIRST FIGURE OF THE NINETEENTH CHAPTER,
where the complete structure of thoracic bones [ossa thoracis] is drawn in its anterior aspect, including the twelve thoracic vertebrae and the twelve ribs on each side, together with the pectoral bone [sternum] formed from several bones.
SECOND FIGURE OF THE PRESENT CHAPTER,
showing the posterior aspect of the complete structure of thoracic bones. It will be helpful also to examine in passing the three figures by which the entire structure of bones is illustrated in three aspects at the end of this Book. 4
THE THIRD FIGURE
includes three vertebrae from the middle of the thoracic vertebrae seen from the right side, together with a middle rib of the same side. By means of this figure the articulation of the ribs to the vertebrae is shown as well as the course of the ribs.
IN THE FOURTH
is illustrated the posterior portion of a rib nearest the vertebrae to bring into clear view the swellings 5 [caput, crista, tuberculum] by which the nine upper ribs are articulated to the vertebrae. We have also broken a part of this rib to show the bony substance [substantia spongiosa, s. compacta, s. corticalis] of the ribs, labeled F.
THE FIFTH FIGURE
displays a portion of the the twelfth rib in the posterior aspect, where it is articulated 6 to the twelfth thoracic vertebra. We have broken this one also, where you see the F, to show the bony substance of the rib.
THE SIXTH FIGURE,
showing the anterior part of the pectoral bone free of rib cartilages [cartilago costalis].
THE SEVENTH FIGURE,
illustrating the posterior aspect of the pectoral bone free of rib cartilages.
|B B 1 , 3||Returning to the figure index, B, B marks the beginning of the cartilaginous substance [cartilago costalis] of the ribs. The line [articulatio costochondralis] between A and B marks its union with bony tissue [os costale].|
|C 1||Union of cartilage of the first rib with the pectoral bone [articulatio sternocostalis I].|
|D 1||Articulation of cartilage of the second rib [art. sternochondralis II] with the pectoral bone, from which the type of joint of the five subsequent ribs may readily be inferred.|
|E 3||Cartilaginous tubercle 7 by which the second rib and the five that follow are articulated to the pectoral bone.|
|F F 1||End of cartilage of the false ribs [costae spuriae VIII-XII], which is seen to be pointed.|
|G 1||Area where cartilage of the eleventh rib is often separated from that of the tenth.|
|H 1||Point where cartilage of the twelfth rib is always separated from that of the eleventh.|
|I I 1||In these places the cartilages of the ribs protrude unevenly, often filling the space between.|
|K K 1 , 4||In this region an elongated depression [sulcus costae] is carved in the inner surface of the middle ribs, to be occupied by a vein, an artery, and a nerve [vasa et nervi intercostales].|
|L 4||Tubercle or capitulum [facies articularis capitis costae] by which the ribs are articulated to the vertebral bodies.|
|M 4||Tubercle [facies articularis tuberculi costae] by which the ribs are articulated to the tips [facies articularis processus transversi] of the transverse processes. These are more or less common to the nine upper ribs. 8|
|N 5||A type of tubercle [caput costae] by which the eleventh and twelfth ribs are articulated to the vertebrae.|
|O 4 , 5||Tubercle [t. costae] located in the posterior portion of the ribs next to the tip of the transverse process, into which is inserted the eleventh of the muscles [m. erector spinae, m. longissimus thoracis] that move the spine. 9|
|Q 4||Interval [collum costae] between L and M, made rough for the purpose of producing a ligament [l. costotransversarium].|
|R 4||This area [angulus costae] too is roughened for muscles 10 which we shall enumerate in this chapter.|
|S, T, V 3||Three joined vertebrae, 11 or the bodies [corpora] of these vertebrae. We have noted other parts or processes of the vertebrae in the appropriate places.|
|X 3||Depression [foveae costales superior et inferior corporis vertebrae] common to two vertebral bodies, to which the head of a rib is articulated. 12|
|a 3||Joint of the rib to the vertebral body [art. costovertebralis].|
|b 3||Depression carved in the transverse process of the vertebra [facies articularis processus transversi], to which the rib is also articulated.|
|c 3||Joint [art. costotransversaria] of the rib to the transverse process.|
|d, e 3||In the topmost vertebra marked S, the depression is also marked, d [fovea costalis superior], like the one marked X between the middle and lowest vertebra. Also, e marks the depression in which you see b written in the lowest vertebra. 13|
|f 3||Region [angulus costae] of the rib most extended posteriorly, from which you may conveniently gauge the course of the ribs as follows: 14 from a and c to f, the rib runs obliquely downward from the vertebra to the posterior; but from A and B to E, the rib is bent back upward to the front in a curve.|
|g, h, i, k 1||The pectoral bone [sternum] is marked with these letters in the first figure. The first pectoral bone [manubrium sterni] is marked g to h; the second [corpus sterni], h to i, the third i to k; k also marks the pointed cartilage [proc. xiphoideus] of the pectoral bone. We shall now approach the pectoral bone more exactly in the sixth and seventh figure.|
|l 6||In the anterior surface of the first bone, a part protruding like a triangle, which could be circumscribed by t, q, and r.|
|m, n 6||Depressed area on each side of the protruding part. 15|
|o 7||Posterior area of the first bone which is seen to be rather concave.|
|p 6 , 7||Part [incisura cartilaginis costalis I] of the first bone to which the cartilage of the first rib is attached.|
|q, r 6||Depression [incisura clavicularis] of the first bone to which the capitula [extremitas sternalis claviculae] of the clavicles are articulated; 16 r also marks the right depression in the seventh figure.|
|s 6 , 7||Area [incisura jugularis] between the two depressions incised for the clavicles, carved out like a moon. 17|
|t 6 , 7||Here the first bone is joined to the second [angulus sterni]. 18|
|u 6 , 7||Common depression [incisura cartilaginis costalis II] of the first and second bone to which the cartilage of the second rib is attached.|
|x, y, z, a, b 6 , 7||Depressions 19 of the second bone to which cartilages of the third, fourth, fifth, sixth, and seventh ribs are articulated.|
|g, d, e 6 , 7||At these locations, distinctions of the second bone sometimes appear in children as if it had been formed of several bones fusing together to make a union. 20|
|z 6 , 7||This [processus xiphoideus] is counted the third pectoral bone; it ends in a cartilage not unlike a sword’s point, marked h. Foramina, in which the inner surface of the pectoral bone abounds, readily show themselves, though they are not marked by letters. 21|
What the thorax is; the chest, and the pectoral bone
We shall call the thorax whatever is contained and circumscribed by the ribs (figs. 1 and 2 show the full array of thoracic bones); we do not include, with Aristotle, 22 the entire trunk of the body (from O to j in the skeletons 23 ), which we measure from the throat to the pubic area. We shall for convenience’s sake call the anterior part of the thorax the chest, pectus, and for this reason the wide bone in this location to which the ribs are articulated will fittingly be called the pectoral or chest bone [sternum], lest we seem negligently to confuse the three words of the Greeks and especially Galen, qw/rac, sth=qoj, and ste/rnon. Thus the pectoral bone, ribs, and twelve dorsal vertebrae, which I previously called thoracic, are the bones of the thorax.
The diligence of the Maker of things in creating the thorax
The industry of the supreme Maker of things, by which the thorax as a whole is neither bony nor fleshy but bone alternating by turns with flesh (the 7th and 8th tables of muscles illustrate this), 25 is admirable. The skull, by contrast, is entirely bony, while the abdomen is constructed chiefly of muscles. These should be considered not in a sketchy or casual way, but exactly and with special care. For since there are three vital organs 26 that regulate a person, bone that is rigid and interrupted by no muscles is placed around the first while the muscles surround the third. But something intermediate, made of bones and muscles, is constructed around the second. Now the brain had no need for muscles, since no part of the skull requires dilation or compression. Therefore the skull is rightly placed about the brain like a helmet or rigid wall. But if there had been some such barrier placed around the organs that serve the liver, such as the stomach, the intestines, and the bladder (the first figures of Bk. 5 illustrate these), and finally if the uterus 27 itself were so constrained, where would the stomach put food and drink? In what direction would the swelling of things gestating in the uterus protrude? Where would excrement be set aside, or how would offspring be expelled in fruitful labor? Could it happen if no muscle 28
Why the abdomen is not also bony
But perhaps someone might interject: “Why should not the abdomen also be made bony, like the thorax? For if such a bony mass formed in alternation with muscles were placed around the belly, it would not interfere with its contraction and dilation, and in addition greater security would be gained for the abdomen.” Whoever asks such a question should be taught that the contents of the belly could not always be expanded and compressed as much as sometimes happens if they were fenced with bone on the outside. If such were the case, women would not be able to conceive, nor would it be possible for a person to eat one’s fill at one time: he would need to eat continually, just as one needs to breathe continually. But it is not at all absurd that one is in constant need of breath: for one spends one’s time in the air, and lives in it. But if we had the same need of food and drink, we should conduct our life quite apart from philosophy and the Muses: forever occupied with eating, we would never pay attention to the finest and most beautiful things. 33 Again, if the bulk of a bony abdomen were as great as women require in the last months of pregnancy, what would be more awkward than such a bulk if after the fetus was expelled she continued to swell so unpleasantly? And at the same time when filled with no other thing which is useful to the human fabric, what would be more awkward than if it did not subside so as properly to embrace the stomach and intestines, and were not placed next to them like a pad or for the sake of heating 34 ? We shall pursue these matters at greater length in the fifth book, 35 and we shall show as well that in the fabric of the belly Nature’s cleverness was so great that she protected organs of the belly that do not require alternating dilation and compression, either placing them beneath other parts, or sheltering them no less than the lungs. For the liver and the spleen are walled in by the ribs, and the kidneys also lie beneath so many other organs, particularly toward the back, because none of these must be expanded, while with the remarkable foresight that we have noted, Nature wished the remaining organs of the belly to be in no way impeded from their functions by a bony structure.
What Nature paid special attention to in constructing the
Since neither respiration nor speech can occur without the thorax, and since the heart first and the lung as well need to be protected by the thorax, it was necessary for the Maker of things to attend to four goals, as it were, in the fabric of the thorax: voice, respiration, and the size of the heart and the lung. The thorax, which has a more or less oval shape, is as large as the size of the lung warranted (figs. 12 and 13, Bk. 6). At the same time, the lung follows the shape of the thorax, not the opposite. In my account of the lung, I shall show with no great difficulty that like the liver, the spleen, or, to a degree, the brain, it required no particular shape,.
The number of ribs
It will now be timely to describe the bones of the thorax in order, and since we have already described its vertebrae (C to D in the fig. for ch. 14 and the figs. in ch. 16), to begin our account with the ribs. Men and women have twelve ribs on either side (numbered 1-12 in figs. 1 and 2); occasionally, there are only eleven, though sometimes we have even observed thirteen. 36 We reported above that thirteen thoracic vertebrae occur more often than only eleven. Each thoracic vertebra is articulated to a single rib on each side.
Men and women have the same number of ribs
It is commonly believed that men lack a rib on one side, and that men have one rib fewer than women. This is plainly absurd, even if Moses did say in the second chapter of Genesis that Eve was created by God out of Adam’s rib. Granted that perhaps Adam’s bones, had someone articulated them into a skeleton, might have lacked a rib on one side, it does not necessarily follow on that account that all men are lacking a rib as well. Aristotle attributed only eight ribs to humans, and was ready to allow that certain members of the race of the Turduli 37 were born with only seven ribs on each side, provided he established this on the actual testimony of some suitable authority. But as in the latter instance Aristotle was willing to support his opinion only with the testimony of others, it is also not unlikely that in the former instance he ascribed eight ribs to man on hearsay evidence, and in this
Symmetry of body among the Ligurians
Yet once in a lecture at Padua while I was discussing the passage of Aristotle just mentioned, I learned from the most promising youths (because of their unique knowledge of literature and civil law) Jacopo Nigro and Francesco Pinelli, 39 members of the Genoese nobility, that Ligurians of the highest rank had been called e(ptapleu/roi, 40 “seven-ribbed,” on ancient monuments, although these people are most distinguished for the excellent symmetry and proper number of their limbs, as they are energetic in battle on land and sea. There are therefore as a rule twelve ribs on each side; the seven upper ones are articulated to the pectoral bone and the vertebrae, as we shall state afterward, while the five lower ones are attached only to the vertebrae, and do not extend to the pectoral bone, but come to an end on the sides of the thorax and are joined to each other by the ends of their own cartilages (F in fig. 1) [cartilagines costales VIII et X], with the sole exception of the twelfth, which is far separated from the eleventh (H in figure 1) and nowhere comes in contact with it. This occurs not uncommonly with the eleventh as well, when it does not reach the cartilage of the tenth (G in fig. 1). Because they are not articulated with the pectoral bone, these five lower ribs are named by the Greeks nothai, which is to say spurious and illegitimate.
The substance and epiphysis of the ribs
All the ribs have it in common that they are made up of a bony (from a through f to A in fig. 3) and cartilaginous (from B to E in the same fig., or A, B in fig. 1) substance, and that they possess an epiphysis (L and M in fig. 4; figs. 4 and 5 show a rib broken at F) at the spot where they are joined to the bodies of the vertebrae and where you will hear they swell out into capitula [facies articulares superior et inferior capitis costae].
The bony substance
The bony substance of the ribs is not the same throughout. Where the ribs are articulated to the vertebrae, and where they form the back, they are much harder and more solid 41 than at the sides of the thorax and next to the region of the chest, where they are constructed of a more spongy [pars ossea, substantia spongiosa] substance covered by a thin scale or layer [pars ossea, substantia corticalis] (figs. 4, 5 show a rib broken at F). This layer is thinnest where it reverts into cartilage.
The cartilage also does not present the same appearance everywhere. The cartilage of the lower ribs is softer; this is perhaps why many people say the false ribs are called xo/ndroj, or cartilage. 42 The cartilage of the upper ribs is harder and more solid, and in aged persons it becomes bony inside 43 as we discover it in sheep, cattle, and nearly all animals of this kind, whose cartilage is made of friable, white, fragile bone inside, wrapped externally in cartilage like a kind of membrane. This is so evident in apes and dogs that Galen said the cartilages of the true ribs are bony while in the false ribs they are pure cartilage. 44 In humans who are not quite advanced in years, the cartilage seems to have given way to a bony nature, while in dogs that are still young and in the animals which we just mentioned, it becomes quite bony. 45
Not all ribs are of equal length
The amount of this cartilage is not the same in all the ribs, and their length is likewise not equal. The first and twelfth are the shortest, then the second and eleventh; all of these have short cartilages. The sixth, seventh, and eighth are the longest, and also have the longest cartilages.
The cartilage [c. costalis] of the first rib is the broadest, as the first rib also excels the others in breadth; the second and third follow this one. The twelfth and eleventh [costae fluitantes XI-XII] are the thinnest of all, and also end in the thinnest cartilages. The middle ribs are of a middle nature, their cartilages becoming wider in their progress away from the bony substance of the rib. 46 For although the cartilages of the six upper ribs form intervals [spatium intercostale] and are equally separated from each other along their entire course, cartilages of the sixth, seventh, eighth, and ninth ribs become from time to time variously broad over their course, and as they join together they fill the intervals between them with their own substance (I, I in fig. 1). The cartilages of the five false ribs [costae spuriae VIII-XII] end in a sharp point (F in fig. 1), unlike the cartilages of the true ribs [costae verae I-VII]. The cartilage of the first rib, firmly attached at its end to the pectoral bone (C in fig. 1) [articulatio sternocostalis I], is wider than where it starts from the rib’s bony substance. The cartilages of the second, third, and three subsequent ribs narrow slightly as they progress, and each ends in a tubercle 47 (D in fig. 1; E in fig. 3) where we shall presently explain they are articulated to the pectoral bone.
Smoothness and roughness of the ribs; their sulcus
The ribs do not have the same smoothness throughout. On their inner surface, where they face the membrane [pleura parietalis, pars costalis] that surrounds them, they all appear smooth and not in the least rough; but the third and those that follow as far as the tenth present a depression [sulcus costae] on their inner surface towards the bottom (K in figs. 1 and 4), carved along their length, not actually visible throughout the length of the rib but most evident where they first leave the vertebrae and begin to run toward the sides of the thorax. This depression is prepared for a branch (G, G in the fig. for ch. 6, Bk. 3) [vena intercostalis posterior] of the hollow vein [v. azygos] which the unpaired vein extends to the ribs; it also carries a branch (k, k in the fig. for ch. 11, Bk. 3) [a. intercostalis posterior] of the great artery [pars descendens aortae], and the nerve (the principal branches [nervi thoracici, rami anteriores, nervi intercostales] following the course of the ribs in fig. 2, ch. 11, Bk. 4) [n. intercostalis] originating from the dorsal medulla. [medulla spinalis]. But because these vessels are large in the middle ribs and always run as a matched set while in the three upper ribs they are small and run a wandering course, it comes as no surprise that the middle ribs have these depressions but the upper ribs do not. The three lower ribs, though large vessels are extended to them, are thin and concave on their inner surface and they still provide safe passage to those vessels without the aid of those depressions. This depression, carved for the passage of vessels, makes the lower part of the rib sharper and thinner than the upper, which looks more blunt and (so to speak) more smoothly rounded. The outer surface of the ribs, which is convex,
The rough tubercle of the ribs
On this outer surface of the ribs where they first leave the transverse processes of the vertebrae, there is seen a rough, uneven tubercle [t. costae] (O in figs. 4 and 5) made to receive the tendons of the eleventh muscle [m. erector spinae, m. longissimus thoracis] that moves the back (D in the 12th table of muscles). The tendons of this muscle are inserted partly into the tips of the transverse processes, and partly into these costal tubercles. Then, where the ribs depart still further from the transverse processes of the vertebrae, they are rough and uneven in this outer, posterior surface [angulus costae] (R in figure 4) and even have a certain rather prominent swelling of sorts to make a suitable point of insertion for the muscle which we shall count the fourth [m. erector spinae, m. iliocostalis thoracis] of the muscles that move the thorax in man, and the sixth in apes and dogs. 49 Not only is this roughness suitable for the insertion of that muscle, but it will be explained that the outer intercostal muscles [m. intercostalis externus] (V in the 11th table of muscles) originate here: these muscles originate in this region next to the vertebrae and run not only from the lower part of the upper rib toward the upper part of the rib below, but also from the outer part of one rib to the outer part of the other. Elsewhere the ribs are smooth and even, unless one were to argue that they are slightly rough on their upper and lower surface where the origin and insertion of the intercostal muscles takes place. On its upper surface where it is very wide, the first rib is characteristically rough and uneven so that the fourth of the muscles that move the back (C in the 8th table of muscles [m. scalenus anterior]) may conveniently take its beginning here.
Articulation of ribs to the vertebrae
Articulation to the vertebrae is not the same for all ribs. The nine upper ribs are attached with a double articulation (a, c in fig. 3), the eleventh and twelfth with a single articulation; the tenth is quite rarely attached to its vertebra with two joints, however differently it may have seemed to Galen, who taught that each rib is attached to the vertebrae by a double joint. 50 The ribs articulated by two nodes put forth two tubercles (one L, the other M in fig. 4): one [L] by which they are articulated into the depression (X, d in fig. 3) incised in the bodies of the vertebrae, the other [M] by which they are supported on the inner surface of the tip of the transverse process [facies articularis processus transversi]. These tubercles 51 [t. costae] correspond to the depressions [fovea] which we stated are carved in the vertebrae when we described their construction. The first rib is articulated by a round tubercle to the body of the first thoracic vertebra, and then ascends the transverse process of the same vertebra until it is articulated to its tip by means of the other capitulum or tubercle. The second rib and the seven after it are always articulated to the common depression of two vertebral bodies [fovea costalis superior, f. costalis inferior] by a capitulum which is not round but protuberant like an obtuse angle; they are attached to the transverse processes in the same way as the first rib, although here too a certain variation arises in the joints because the depressions are not carved out at the same spot in the transverse processes. This is because the transverse processes of the upper vertebrae have their depressions cut in the lower portion of their inner surface, but in the lower vertebrae they are in the upper portion (as we stated above against the view of Galen), and in the middle vertebrae they are in between. That the articulation of the ribs to the body of the vertebra is higher than that which the ribs effect to the transverse processes, as much higher as the tip of the transverse process is lower than the depression carved in the vertebral body, I believe goes without saying. The articulation of the three lower ribs, which takes place only on the body of the vertebrae and in depressions not as deeply hollowed out, occurs also with not very protuberant capitula (N in fig. 5). In this way the ribs are attached to the vertebrae. What type of joint 52 they form with the pectoral bone [sternum], and along what course they pass forward from the vertebrae, we shall find the opportunity to explain as soon as we have added the construction of the pectoral bone to our account. This would be truly easy to explain if the human bone corresponded to that of apes, dogs, calves, and suchlike animals.
Description of the pectoral bone in quadrupeds
In these animals (as can be seen even while eating), 53 the pectoral bone consists of seven bones, not so different from each other in form. In dogs, pigs, and sheep, they look alike; but in apes and squirrels, because of the articulation of the clavicles, the first and highest bone is somewhat wider than the others. These seven bones are wider than they are deep or thick, and where they are joined together they are somewhat wider than they are in the middle. Their connection by intervening cartilage is sometimes so loosely accomplished that it differs only slightly from the structure of the vertebrae (R, R in the fig. for ch. 14) [discus intervertebralis], but this connection belongs to the category of symphysis or union, like that of the epiphyses with their bones. But it is possible to see this connection even in quite aged cattle. Hence I wonder about Galen in his book De ossibus, how he could have written that the bones of the chest are joined by synarthrosis, even though they are put together with neither harmonia [sutura plana] nor suture and much less with gomphosis, these being the types of juncture which he included under synarthrosis 54 in the beginning of his book. 55 In the sides of these points of juncture a depression [incisura cartilaginis costalis II] is carved on either side, to which a tubercle of the cartilage [cartilago costalis] into which the ribs revert is joined. At the point where the first bone of the sternum [manubrium sterni] meets the second [corpus sterni],
Description of the human pectoral bone
But if you had studied the human pectoral bone (all of figs. 6 and 7) (which is in general broad, though by far the shortest if compared with the bones of other animals), you would notice that it is much different. 58 For I can affirm with certainty that I have never found seven bones in the human pectoral bone, 59 nor in man are these bones always found in the same number. In adults, about three are seen, quite different from each other. The first [manubrium sterni] is remarkably wide (g to h in fig. 1, and in 6 and 7 from s to t) and also rather thick, but only to the degree that its thickness is greatly exceeded by its breadth. On its inner or posterior surface (o in fig. 7) where it faces the cavity of the thorax, this bone is slightly concave; on the anterior it is convex, and much thicker in the middle lengthwise than at its sides, for it is depressed on the sides of its anterior surface and made thin to match the thickness of the cartilage of the first rib (p in figs. 6 and 7) [incisura cartilaginis costalis I]. In the middle, though, it protrudes in a triangular shape (q, r, l in fig. 6) for strength. The upper part of the bone (p, q, s, r in figs. 6 and 7) is much thicker and broader than the lower (t, u in figs. 6 and 7), and has on each side a single long depression [incisura clavicularis] (q, r in figs. 6 and 7) cut towards the posterior and lined with cartilage: to this the head [extremitas sternalis] of the clavicle (A in fig. 1, ch. 22) is articulated. Between these depressions, because of their swelling inner sides, this first bone is lunate (s in figs. 6 and 7) in this upper surface and shows a kind of fovea [incisura jugularis] which we properly call sfagh/ and iugulum, “throat,” and laymen the upper fork. 60 The lower part of the bone (t in figs. 6 and 7) is quite rough and is so loosely attached by cartilaginous ligament 61 to the second bone [corpus sterni], which I shall now describe, that the connection of these bones never goes unnoticed, and its motion is sometimes actually perceived during deep breathing. The second bone (from h to i in fig. 1) is much wider than it is thick, and denser on its upper surface where it is attached to the first bone (t in figs. 6 and 7) than it is near the bottom (near e in fig. 6). But nowhere is it as wide as the upper part of the first bone. At the point where this second bone is joined to the first, a bluntly angled depression [incisura cartilaginis costalis II] (u in figs. 6 and 7) is carved on either side of the joint, common to both bones and lined with cartilage; to this the cartilage of the second rib (D in fig. 1), protruding like the tip of a rather blunt triangle, is articulated. Besides this depression, the present bone forms many others [incisurae cartilaginis costalis] (x, y, z, a, b in figs. 6, 7) on each side in a similar manner, pushed in at a blunt angle; these are separated at not at all uniform intervals. The first depression [incisura] on each side belonging to this bone, made for the cartilage of the third rib, is farther from the depression incised for the second rib than from the second depression peculiar to this bone, carved for the fourth rib. 62 Again, a greater interval stands between the second depression and the third than between the third and the fourth, so that the depressions carved in this bone for the sixth and seventh ribs adjoin each other and are scarcely separated; 63 they are also not so deeply excavated as the higher ones. This second bone by itself receives the cartilages of the third, fourth, fifth, sixth, and seventh ribs which protrude like the cartilage of the second rib (E in fig. 3). In children, it is seen to have been formed from several bones (g, d, e in fig. 6) knit together by the symphysis or fusion of cartilage. But this knitting-together 64 is never comparable to an ape’s or a dog’s structure of bones, since it is much harder to see and the lower bones are much shorter than the upper. In cemeteries the second bone is almost always unearthed in one piece and separate from the first, just as the vertebrae are brought up separated from each other, although by chance you will observe another type of structure in the second bone, as if it was made of several bones. This will most often appear where the cartilage of the third rib is articulated to the bone (g in fig. 6) 65 , and next often where the cartilages of the fourth ribs are joined into the pectoral bone (d in fig. 6) 66 . Now the third bone [processus xyphoideus] (from i to k in fig. 1, z in figs. 6 and 7) is scanty, and is joined to the inner part of the lower surface of the second bone by the same method 67 as it has been explained the first is joined to the second; it is joined to the second bone where the cartilages of the seventh ribs are articulated to the lowest part of the second bone 68 . This bone is moderately wide and thin, and in its lower portion it reverts into a pointed cartilage. 69
Comparison of the pectoral bone to a sword
But you will not infrequently find it is missing, and you will see a pointed cartilage (k in fig. 1, h in figs. 6 and 7) attached where the cartilages of the seventh ribs meet and are articulated to the second pectoral bone. If you now join the three pectoral bones together, you will see the image of a sword handle. The upper part of the first bone, which is rather wide, will correspond to that part of the handle which lies below the little finger when gripped. The second bone will match that part which the entire hand embraces within it, where the depressions made for the rib cartilages will be like the ones in which the fingers can be braced. 70 This is the function the depressions would have which we seek in swords from the roughness of the handle, whenever we take the trouble to cover the handle with twisted and knotted cords
The pectoral bone is crescent-shaped on both sides
The words of Celsus, where he wrote that the pectoral bone is crescent-shaped on both sides, support this view. 73 For he made this false statement concerning apes and dogs even though nothing of the sort appears in them. For in man the first pectoral bone is much wider above and the second is wider below, than when they have been joined together.
The substance of the pectoral bone
The substance of the pectoral bone is quite soft and spongy, 74 and is covered on its anterior surface by a more uninterrupted scale [pars ossea, substantia corticalis] than on its posterior; for the posterior scale has many foramina of different sizes which are not open at both ends but only provide access to vessels [arteria thoracica interna] (following A, A in fig. 2, Bk. 6) by which this bone is nourished. These foramina are more conspicuous in the first bone [manubrium sterni] to the same degree that the thickness of this bone exceeds that of the second [corpus sterni].
The use of the pectoral bone
That the pectoral bone was created to stabilize the ribs that form the space of the thorax in a series of rings, is I think known to all. Likewise it is known that it serves in the second place as a bulwark and performs those functions for man that the thoracic bones as a class provide, which we stated at the beginning of this chapter.
The use of the pointed cartilage
The cartilage [processus xiphoideus] with which the pectoral bone ends in a point is also a protection for the things beneath, and is popularly called malum granatum, the pomegranate, 75 I think because it resembles a tip of the pomegranate blossom. Also because of its shape, laymen call it the epiglottal cartilage, from its resemblance to the operculum [epiglottis] of the larynx (figs. 12 and 13, ch. 38), which in appearance is not altogether unlike 76 the cartilage of the pectoral bone. We shall append a large number of such names to the end of this book together with the names of other bones.
The course of the ribs
Nothing remains now to be added, except perhaps the course of the ribs, which is far different in the bones of the ribs than in their cartilages. When the rib bones [costae] (from a through c to f in figure 3) first leave the vertebrae, they slant downward to the posterior, and from here (from f to A in figure 3) they decline to the sides of the thorax, always obliquely downward towards the front until they end in cartilage extending in a curve upward to the anterior (from B to E in the same figure). Thus when the ribs first put forth cartilage [c. costalis] they bend in an arc and an angle more or less upward. This course of the ribs (see the skeletons, particularly the second) is evident not only in those which are attached to the pectoral bone, but also in all the rest with the possible exception of the twelfth, whose cartilage faces quite obscurely upward. This curvature is seen especially in the middle ribs, which is to say the sixth, seventh, eighth and ninth, while in the upper and lower ones it is more subtle. 77