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The human sternochondral joints.

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T H E HUMAN STERNOCHONDRAL JOINTS
D. J. GRAY A N D E. D. GARDNER
Department of A n a t o m y , S t a n f o r d University, California
ONE TEXT FIGURE AND THREE PLATES
(TWENTY-FOUR FIGURES)
INTRODUCTION
The sternochondral joints, except for the first, are usually
described a s being freely movable and possessing a joint
cavity. They are therefore classified as diarthrodial joints.
A “tendency” to become synchondrodial has been noted,
however, especially in the sixth and seventh joints. This
process has been attributed to ageing.
A transverse intra-articular fibrocartilaginous ligament is
described for the second sternochondral articulation when a
cavity is present. This is reported t o be of fairly constant occurrence, and to be found occasionally in the other joints.
Sappey (1867) noticed that this ligament is located in the
anterior part of the articulation and observed that sometimes it is vestigial, while at other times it completely fills the
joint cavity. Fick (’04) found the ligament to be thinner
behind than in front, and observed that it occasionally fails
to reach the dorsal capsular wall, leaving a space by means
of which the upper and lower parts of the cavity communicate.
Henle (1871) found the intra-articular ligament t o be variable in position. Sometimes it occurs higher than the midplane of the joint cavity, sometimes lower, and at other times
is totally lacking. Hyrtl (1882) considered the ligament to be a
true prolongation of the fibrocartilage uniting the manubrium
with the body of the sternum.
I n order to observe the frequency of the presence of the
intra-articular ligaments, Tschaussow (1891) studied the
235
236
D. J. GRAY AND E. D. GARDNER
sternochondral joints of eighty-nine cadavers. I n the second
joint they were absent in three bodies. I n the third joint
they were present eighteen times, in the fourth nine times,
and in the seventh four times. No figures were given for
their presence in the fifth and sixth joints.
Musgrove (1892-93) found the second joint divided into
two cavities on the right side in eleven out of eighteen bodies.
There were double cavities in the third joint five times, in
the fourth twice and in the fifth twice. The sixth and seventh
right joints showed either a single cavity or none at all. On
the left side there were two cavities in the second joint ten
times, in the third seven times, in the fourth twice and in the
fifth once. No double cavities were observed in the sixth and
seventh joints of the left side.
I n regard to the presence of an intra-articular ligament in
the second joint, Bryce's ('15) figure of about 60% agrees
more closely with that of Musgrove than that of Tschaussow.
The investigations of Tschaussow have been quite widely
accepted as f a r as the appearance of cavities is concerned.
He claimed the appearance of whitish bands to be the first
indication of future joints and asserted that cavities appear
first at the union of the sternum with the third costal
cartilages in a 5-month fetus. The cavities of the second
articulation appear at a shghtly later stage, and still later
in the remaining joints. Contrasted with these observations
are those of Pohlmann ( '33) who claimed never to have seen
cavities in embryonic sternochondral joints.
MATERIALS AND METHODS
The sternochondral joints of a series of twenty-two human
embryos and fetuses,I ranging in age from 6 weeks to term,
were studied in an attempt to determine the time of appearance of the cavities. All of this material had been preserved
in 5% formalin. The four youngest specimens were washed,
1 Four of the fetal specimens were obtained from Washington University School
of Medicine, St. Louis, Missouri, during a year spent by the junior author in
the Department of Anatomy there.
S T E R N O C H O N D R A L JOINTS
237
dehydrated, embedded in Tissuemat, serially sectioned in a
transverse plane a t 10 micra, and stained by the Mallory-Azan
method. The sterna, including parts of the costal cartilages,
were removed from the eighteen older fetuses and were then
washed and decalcified in 57% nitric acid. Eight of these
were dehydrated, ernbedded in Tissuemat and cut serially in
a frontal plane at 12 micra. Alternate sections were mounted
and stained by the Mallory-Azan method. The remaining
ten sterna and costal cartilages were embedded in nitrocellulose and cut serially in a frontal plane at 50 micra. Every
third, fifth or tenth section, depending on the size of the
sternum, was stained with hematoxylin and eosin and mounted.
Studies of adult articulations were made on dissecting
room material. The joints of ninety-six bodies, ranging in age
from 33 to 92 years, were examined. The sterna, with the
medial portions of the costal cartilages, were removed from
the cadavers and sectioned in a frontal plane so as to bisect
the joints. Breakage, o r deviations from the line of sectioning, rendered a few articulations unfit for study. Examinations of the suitable joints were made to determine grossly
the frequency of the presence of cavities, and of strands or
ligaments crossing the cavities. Representative joints were
removed from these specimens and decalcified in 5% nitric
acid. They were then washed and dehydrated. Of these, approximately one-half yere infiltrated with nitrocellulose dissolved in methyl benzoate and subsequently embedded in
Tissuemat, cut serially in a frontal plane a t 10 micra, and
stained by the Mallory-Azan method. The remainder were
embedded in nitrocellulose, cut serially in a frontal plane at
15 micra, and every tenth section was stained with hematoxylin and eosin.
OBSERVATIONS
D eve1o pnaent
(to term)
I n all the embryos there were direct cartilaginous unions
of the sternal bar with the costal cartilages (figs. 2 and 14).
The future sternochondrd joints were indicated at 34 months,
238
D. J. GRAY A N D E. D. GARDNER
however, when zones of demarcation were present in the precartilage of these areas (figs. 5 and 15). The parts of the costal cartilages and the sternum adjacent to these demarcation zones were acidophilic. At this or slightly later stages
the zones themselves had lost their cartilaginous nature and
had progressively assumed the character of a loose coiinective tissue. After the cartilaginous character was definitely lost, the cells within the demarcation zones increased
in size and became arranged in parallel rows between the
fine bundles of collagenous fibers which passed transversely
across the zones (figs. 3 and 17). The tissue thus formed
bore some resemblance to early fibrocartilage.
Minute spaces appearing between the rows of cells and
among the fibers which traversed these zones coalesced and
thus became somewhat larger. This process was especially
apparent in the central parts of the zones although the first
definite joint cavities to appear were usually at the periphery
(figs. 4 and 16). The time interval between the appearance
of the demarcation zones and the formation of cavities varied
considerably. I n the second joint, cavities were usually formed
during the third month, shortly after the demarcation zones
were first indicated. If not, cavities in this and other joints
usually appeared a t later times during fetal life.
I n one 3&1ionth-old fetus cavities were present bilaterally
in the second sternochbndral joint and were separated into
upper and lower parts by an intra-articular ligament which
was continuous with the tissue separating the manubrium
from the body of the sternum (figs. G and 18). I n the other
specimens of this age cavities were present only in the upper
halves of the joints. Except for one full-term fetus in which
they were absent in all of the joints, there were cavities in
the second on one or both sides in all fetuses from 34 months
to term.
Cavities appeared in some third joints at 4 months. I n two
out of seven specimens they were unilateral. Bilateral cavities were not present in the third joint until term, and then in
only one specimen out of four a t this age.
STERNOCHONDRAL JOIX’TS
239
Cavities were found in neither the fourth or fifth joints
except in one full-term fetus in which they were present bilaterally in both joints. Cavities were found in the sixth and
seventh joints only twice; once in a fetus 6 months old and
in another at term. These were all bilateral. I n one fetus
at term, cavities were found in every sternochondral joint.
d (1ul t joiia t s
Gross appearance. Variations from the usual textbook
descriptions of the second sternochondral articulation were
frequently encountered. Only 30% of ninety-two right second
joints had cavities both above and below the intra-articular
ligament. Eight per cent showed single cavities, due t o the
absence of the ligament while 11%had no cavities. In 51%
either the cavities were crossed by strands or one cavity
was absent. When one cavity was absent, it was almost
always the upper.
On the left side 42%) of the second joints had complete
upper and lower cavities. Five per cent had complete cavities, but lacked intra-articular ligaments. Those without cavities amounted to 10% of the total examined. Forty-three
per cent exhibited strands or the complete absence of an upper
or lower cavity. As on the right side it was the upper cavity
which was usually absent.
The percentages of all the articulat on8 which had cavities,
110 cavities or partial cavities are shown in table 1.
The joints other than the second also varied considerably
in gross appearance when they were examined in frontal
sections. The occurrence of strands which crossed some of
the cavities from the sternal articular facets to the costal
cartilages was most striking. These differed in size, number
and direction. They varied from exceedingly thin strands
to those of a thickness comparable to that of the intra-articular ligament of the second joint. They usually crossed the
cavity obliquely, but sometimes transversely. Partial 01- complete obliteration of the joint cavity was sometimes accom-
240
D. J. GRAY A N D E. D. GAHDNER
plished by a solid mass of tissue similar in appearance to
these strands.
Other irregularities were sometimes present. There were
occasionally small knobs or protuberances one one articular
facet which fit into corresponding depressions on the opposed
surface. Where cavities were partially or completely present,
the articular cartilages had a dense appearance, were whitish
in color and lacked the usual translucence of hyaline cartilage.
The line of demarcation between the hyaline cartilage of the
TABLE 1
Incidencr.9
of
cavities and xtrands in sternochondral ioints from the dissecting room.
FILEQUBNCIIS
IN PER CENT ( NEAR,ESII.ROUND NUMB&&)
Number of
cases
No cavities
Second right
Second left
92
89
11
10
38
47
51
48
Third right
Third left
95
95
19
23
4n
35
41
42
Fourth right
Fourth left
94
93
23
40
43
35
25
Fifth right
Fifth left
96
94
25
34
41
29
34
37
Sixth right
Sixth left
94
94
52
59
26
20
22
21
Seventh right
Seventh left
88
59
71
17
15
24
14
86
Uninterrupted Cavities crossed
by strands
cavities
31
costal cartilage and this tissue which lined its articular end
was ordinarily quite abrupt and easily visible t o the naked
eye. Similarly; on the sternal side the demarcation between
bone and articular cartilage was sharp.
The presence of characteristic intra-articular ligaments
in joints other than the second was rare. I n a very few instances a band crossing the middle of the third articulation
resembled somewhat the ligament of the second joint, but in
joints below the third no such band was observed.
Microscopic appearauzce. Fibrocartilage was found in all
the sternochondral joints examined, whether or not cavities
were present, and constituted the tissue intervening between
STERNOCHONDRAL JOINTS
241
the costal cartilages and the sternal facets. I n the second
joint the fibrocartilage forming the articular surfaces was
directly continuous with the cartilage separating the manubrium and the body of the sternum (figs. 8 and 20). When
cavities were present in any of the joints they usually divided
the fibrocartilage into almost equal parts and ordinarily extended to the capsule above and below.
On the sternal side of all the sternochondral joints there
was a layer of hyaline cartilage which separated the art-cular
fibrocartilage from bone. This layer was sometimes extremelp
thin or even deficient in places (fig. 21). I n some cases small
areas were found in which the compact bone of the sternum
was lacking and thus the bone marrow lay adjacent to either
hyaline or fibrocartilage. Occasionally blood vessels were
seen passing through these areas.
A sternal articular fibrocartilage was often comparatively
thick; if it was, the fibrocartilage on the opposite side of thc
cavity was usually thin (fig. 9). That part of the fibrocartilage adjacent to the cavity was acellular, amorphous and quite
acidophilic (fig. 22). This was true also of the free borders
of the strands which crossed the cavities (fig. 23).
On the costal side of the joint cavity the transition between
fibrocartilage and costal cartilage was in some cases quite
abrupt, and in others rather gradual with the collagenous
fibers of the fibrocartilage continuing for a short distance
into the hyaline cartilage. Both articular fibrocartilages could
usually be traced into the perichondrium o r periosteum at the
upper or lower parts of the joint. I n a few cases, however,
there was a direct continuity of these cartilages, either above
or below the cavity (fig. 10). They were rarely continuous
at both ext r emiti e s.
The bands crossing the joint cavities were extremely variable. They sometimes occupied one-hdf o r more of the cavity, while a t other times they were sufficiently small t o be almost unrecognizable under low magnifications of the microscope. While most of them crossed the cavities in an oblique
direction from superior t o inferior and from anterior to pos-
242
D. J. GRAY A N D E. D. G A R D S E R
terior, there were occasionally those which were transverse
or nearly so. I n all the sections studied the strands were composed of fibrocartilage (figs. 11and 2 3 ) .
I n joints which had no cavities, the fibrocartilage covering,
the sternal facet was directly contiiiuous with that covering
the costal cartilage, with no line of differentiation between
the two (figs. 12, 13, 24 and 25). There was no constant arrangement of the cells and fibers of the fibrocartilage. At
times they were arranged irregularly (fig. 2 5 ) . More commonly, however, the cells and fibers had a tendency toward
a more o r less longitudinal arrangement a t the upper and
lower limits of the joint, while in its middle part columns of
cartilage cells r a n in a transverse direction and w7ere separated
bj- collagenous fibers passing in the same direct:on (fig. 24).
A less dense arrangement of both cells and fibers mas noticed
as the center of the joint was approached.
I n the right third joint of one specimen a peculiar extension of the capsule was noted. Dividing the joint cavity
into two parts, in much the same manner a s a n intra-articular
disc, was a band of tissue continuous above and below with
the capsule. This band a t the periphery had a synovial covering and contained blood vessels. Centrally it became amorphous, acellular and acidophilic.
I n a few joints loose connective tissue with numerous small
blood vessels was located a t the superior and inferior extremities of the joint, and in one this very vascular tissue conipletely
obliterated the cavity.
Ossification of the sternal extremities of the costal cartilages did not involve the fibrocartilage. It was also observed
that even in old age the body of the sternum iriay not be completely ossified. Areas adjacent to the sternochondral joints
now and then contained sinall patches of hyaline cartilage
ccmpletely surrounded by bone.
DISCUSSION
The appearance of cavities in the sternochondral articulatioiis as shown by this study is subject to considerable varia-
STERNOCHONDRAL JOINTS
243
tion. When the investigations are confined to embryonic and
fetal material, the order of appearance of cavities cannot
be learned for all joints since some cavities may appear after
birth. It seems safe to state, however, that the first cavities
to appear are those of the second articulation. A cavity in
the third joint usually follows the second a t a slightly later
stage, although in one 6-month fetus bilateral cavities were
present in both sixth and seventh joints, while the cavity of
the third joint was still unilateral.
The initiation of fetal respiratory movements as postulated
by some investigators to be responsible for the formation of
cavities does not seem to be a reasonable explanation, inasmuch as cavities appeared in some fetuses as early as the third
month, while in others they were still not present at the time
of birth. The order of appearance of cavities as given by
Tschaussow was not confirmed by this study, nor do these results agree with those of Pohlmann.
With the lack of specimens from birth to 33 years of age,
the question arises as to whether joints which showed no cavities in the adult ever developed them, since the percentage
of fetuses showing an absence of cavities was comparable to
that of the adults in which the cavities were absent.
The manner in which the fibrocartilage appears in the adult
joint gives rise to speculation. It was stated earlier that the
tissue which lay in the demarcation zones had some resemblance to early fibrocartilage. It may be postulated that this
tissue never disappeared, but remained to become the fibrocartilage in the adult joint. This does not, however, account
for the fact that after the appearance of cavities in the fetal
joints, the tissue of the demarcation zones disappeared and
there remained only the articular hyaline cartilages of the
sternum and costal cartilages (figs. 7 and 19). Yet in the adult
all the sternochondral joints examined contained fibrocartilage.
It is possible that the fibrocartilage may arise through a
transformation of the hyaline cartilage. The small amount,
or lack of hyaline cartilage on the sternal articular facet
244
D. J. GRAY A N D E. D. G A R D N E R
seems to suggest this. This provides no explanation, however, for the manner in which the fibrocartilage crosses the
joint cavity.
It is also possible that the cartilage may arise from the
capsule, or even from the sternal bone parrow, since the
latter may be in direct communication with the fibrocartilage.
Moreover, the time of appearance of adult fibrocartilage here
is unknown. It is to be hoped that specimens of the ages not
now available will aid in solving these problems.
I t is known that fibrocartilage may appear in joints which
are subject to unusual mechanical stresses and there is the
possibility that stresses sufficient to bring about this change
occur in the sternochondral articulations. Although they
carry no weight, the repetition of movement and the movements in many directions bring about conditions to which
other joints are not subjected.
It is apparent from figure 1 that the percentage of joints
lacking cavities increased from the second to the seventh
joints. Coiiversely the percentage of joints showing complete
cavities and those having strands tended to decrease from
the second to the seventh. These findings are impossible to
correlate with an assumption that cavities are necessary for
movement since it is well known that the lower ribs are subject to greater ranges of motion during respiration than the
upper.
From these observations it seems that the use of the term
intra-articular ligament is not justified except when it is used
in connection with the second joint. What may appear grossly
to be a band o r ligament often proves to be a number of separate strands, and these strands are not necessarily parallel t o
each other.
There is a strong likelihood that strands running transversely across the joint cavity would tend to restrict motion.
The usual direction of the strands, however, is oblique, and
they may run in such a way as to make considerable movement
possible, although it is to be admitted that the presence of
245
STERNOCHONDRAL J O I N T S
strands suggests a smaller amount of movement than does a
complete cavity.
The absence of cavities in the sternochondral joints does
not imply lack of motion. They are absent much too frequently to think that movement was lacking or even greatly
restricted. A certain amount of compression of the fibrocartilage in such joints necessarily occurs.
IT
LEFT
S T E R N O C ti O N D R A L
1
JOINTS
Fig. 1 Graphs illustrating the incidence of joints with complete cavities,
with no cavities and with cavities crossed by strands.
The question of age in connection with the presence or
absence of cavities was considered, and results of the findings
were tabulated according to the age of the cadaver. No correlation was observed. The joints in younger bodies were as
apt t o lack cavities as those of the older. On the other hand
cavities were as frequent in the older specinlens as in the
younger ones. It should be understood that the factor of
age is not necessarily ruled out by these findings. It is probable that joints from a series of bodies varying in age from
birth to 33 years will show some progressive changes.
SUMMARY
1. The times of appearance of cavities in the sternochondral joints are subject t o wide variation. They were present
246
D. J. GRAY AND E. D. OARDNER
in some joints in the 3+-month fetus. On the other hand a
fetus at term showed cavities in none of the sternochondral
joints.
2. The cavities of the second joint were the first to make
their appearance. The cavities of the third appeared shortly
afterwards, at least unilaterally. Insufficient material precludes establishing with certainty the order of appearance
of the remaining cavities. Present indications are that those
of the sixth and seventh joints follow the third in appearance,
while those of the fourth and fifth appear last.
3. The adult articulations showed a decreasing percentage
having complete cavities in passing from the second to the
seventh joint. The percentage having strands across the
cavity also decreased from the second to the seventh, while
the proportion exhibiting complete lack of cavities increased
in this progression.
4. The intra-articular ligament of the second joint was
absent in 8% on the right side, 5% on the left. If either upper
o r lower cavity of this joint was absent, it was almost
always the upper.
5. All sternochondral joints contained fibrocartilage between the sternal articular facets and the costal cartilages.
Any cavities which were present divided it into two articular
fibrocartilages.
6. Strands crossing the cavities were always composed of
fibrocartilage. These strands usually passed obliquely, rarely
transversely across the cavities. They varied in size and
number.
7. Age does not seem to be a factor in determining the
presence or absence of joint cavities in subjects from 33 to
92 years.
LITERATURE CITED
BRYCE,
T. H. 1915 Quain’s Elements of Anatomy, vol. 4, part 1. Edited by
E. A. Schafer, J. Symingtoii and T. H. Bryce, New York.
FICK,RUDOLPH 1904 Handbuch der Anatomie und Mechanik der Gelenke,
erster Teil, Jena, S . 131-136.
HENLE,J. 1871 Handbuch der systematischen Anatomie des Menschen, erster
Band, zweite Abteilung, zweite Auflage, Braunschweig, S. 52.
STEBNOCHONDBAL JOINTS
IIYRTL,J.
247
1882 Handbuch der topograpliischen Aiiatomie und ihrer praktisch
mediciriisch-chirugischeii Anwendungen, siebeiite in den praktischen
Anwendungen namhaft vennehrte Auflnge, erster Band, Wien, S. 601.
MUSGROVE,JAMES
1692-93 The Cos:o Steriial Articulations. Jour. Anat. and
Physiol., vol. 27, pp. 1-1.
POHLMANN,
H. 1933 Eiitwieklung Wachstum und Altersveranderungen der
Iiitersternalsyiiehondrose init Beriieksichtigung der zweiten Sternoeostalverbindung. Ztsclrr. f . Konstitutionslehre, Bd. 17, S. 6 4 1 4 8 7 .
R A I ' P ~ , PH. c. 1867 Trait6 d 'anatomie descriptive, deuxikme Mition, tome
premier, Paris.
TSCHA~JSSOW,
M. 1891 ZU'I Frage ukwr die Rternocostalgelenke und den Respirationtypus. Anat. Anz., Bd. 6, S. 512-524.
PLATE 1
EXPLANATION OF FIGURES
2 Cross secton of a 2-month-old human embryo in which the sternal bars and
some costal cartilages are cut in the frontal plane and are directly continuous
with each other. X 2;.
3 Frontal section through a fourth sternochondral junction of a full term
fetus. A demarcation zone is evident. Note numerous blood vessels in sternum
and costal cartilage. X 5.
4 Frontal section through steruum and costal cartilages of a 4-month fetus.
That p a r t of the second steruocliondral junction in the outlined area is illustrated in figure 16. , X 5.
5 Frontal section through the sternum and costal cartilages of a 34 month
fetus. Tho demarcation zone of the third sternocliondral junction is illustrated
in figure 15. X 5.
6 Frontal section through the second sternochondral junctions of a 34
month fetus. The junction which is outlined is illustrated in figure 18. x 5.
7 Frontal section through the second sternochondral junctions of a full term
fctus. The cavity indicated by the arrow is illustrated in figure 19. x 5.
8 Frontal section of a n adult left second sternochondral joint in which upper
and lower cavities are separated by a n intra-articular ligament. Figure 20
illustrates the area outlined. , X 5.
9 Frontal section through 311 adult right third sternochondral joint in which
there is a slit-like cavity and a thick pa.d of fibrocartilage on the sternal side.
See figure 21 for area outlined. X 5.
10 Frontal section of a n adult left third sternochondral joint. An irregular
cavity bounds a protuberance on the costal side. There are a few fibrocartilaginous
strands a t the periphery of the cavity. The articular fibrocartilages are continuous at tho lonrer part of the cavity. The outlined area is illustrated in figure
22. x 5.
11 Frontal seckion of a n adult left fifth sternocliondral joint. A large oblique
band crossing the cavity is indicated by a n arrow and is also illustrated in figure
23. ,X 5.
12 Frontal section through a completely closed adult right fourth joint. x 5.
13 Frontal section of a completely closed adult left second joint. The fibrocartilage occluding the cavity is directly continuous with t h a t separating the
manubrium from the body of the sternum. .x 5.
248
PLATE I
STERNOCHONI)RAI, J O I N T S
D. J. QRAY AND El. D. GARDNE'B
249
PLATE 2
EXPLANATION OF FIG U RE S
11 Frontal section through three stcriioclioiidral junctions of figure 2. X 60.
1.5 Frontal section through an early demarcation zone of a third sternochondral
junction of figure 5. X 60.
16 Frontal section through the second sternochondral juuction of figure 4.
bhrly cavity formation indicated a t periphery of junction. X 60.
1 7 Frontal section through the third sternochondral junction of figure 3.
Trailsverse striations of a n advanced demarcation zone. x 60.
18 Upper and lower cavities i n a second sternochondral junction of figure
6. x 60.
l!) Well advanced cavity n ith articular hyaline cartilage of second sternochondial junction of figure 7. x 60.
250
sTLRNOCHONDRAL JOlNTR
D J QllAY A N D F
PLATE 2
L, 0ARI)Nh.IL
251
PLATE 3
EXPLANATION OF FIGURES
20 Cavity, articular fibrocartilage and a fibrocarti1;rginous strand of second
sternochondral junction of figure 8. x 60.
2 1 Heavy fibrocartilaginous strand (arrow) crossing t h e cavity of the third
joint illustrated in figure 9. Note the fibrocartilage i n contact with compacta of
aternurn in lower right corner. X 60.
2 2 Articular fibrocartilages and a small fibrocartilaginous strand of the left
third sternoehondral joint shown in figure 10. Note amorphous character of f r e e
border of articular fibrocartilages. X 60.
23 Fibrocartilaginous band crossing the cavity of the fifth joint illustrated
i n figure 11. Note again the amorphous free border of the fibrocartilage. X 60.
24 Fibrocartilage obliterating the cavity of the right fourth joint illustrated
in figure 12. Note the transverse arrangement of the cells and fibers near the
ccntral part of the joint, and the longitudinal arrangmeiit toward the periphery
in the iipper right corner. X 60.
25 Fibrocartilage obliterating the cavity of the left second joint shown in
figure 13. Here the cells and fibers are arranged ill R r e l y irregular manner. x 60.
252
PLATE 3
S T E R N O C H O N U R A L JOI NTB
D. J. QRAY A N D E . D. G A R n N X R
253
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