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=The Sternum - Its Early Development and Ossification in Man and Mammals=
=The Sternum - Its Early Development and Ossification in Man and Mammals=


By Professor Paterson (1900)


Paterson (1900)
Liverpool. (PLATES II., III.)


THE STERNUM : ITS EARLY DEVELOPMENT AND OSSIFICATION IN MAN AND MAMMALS.1
(Preliminary Communication).  


(Preliminary Communication). By Professor PATERSON, Liverpool. (PLATES II., III.)
* Read at the Manchester meeting of the Anatomical Society of Great Britain and Ireland,1900.


IN the following pages the record is given of some recent observations upon the early development and ossification of the
sternum in man and certain mammals (chiefly rodents). The
morphological problems associated with the anatomy and development of this bone are so numerous and important, that it has
seemed desirable to make, in the first place, a brief statement
of certain facts of development, so as to clear the way for future


discussion and consideration of the more general anatomical


questions in which the sternum is implicated.
In the following pages the record is given of some recent observations upon the early development and ossification of the sternum in man and certain mammals (chiefly rodents). The morphological problems associated with the anatomy and development of this bone are so numerous and important, that it has seemed desirable to make, in the first place, a brief statement of certain facts of development, so as to clear the way for future discussion and consideration of the more general anatomical questions in which the sternum is implicated.


I. EARLY DEVELOPMENT.
==I. Early Development==


The following observations upon the early development of the
The following observations upon the early development of the sternum were made on rat and human embryos.
sternum were made on rat and human embryos.


(at) In a series of continuous sagittal sections through aihuman
(at) In a series of continuous sagittal sections through aihuman embryo in the second month, prepared and placed at my disposal by Professor Paul, the first anlage of the sternum (fig. 1) is to be seen as a dense conglomeration of mesoblastic cells, occupying the anterior part of the thoracic wall in the middle line, and tapering off posteriorly: disappearing as a separate structure about the middle in length of the thoracic wall.
embryo in the second month, prepared and placed at my disposal by Professor Paul, the first anlage of the sternum (fig. 1)
is to be seen as a dense conglomeration of mesoblastic cells,
occupying the anterior part of the thoracic wall in the middle
line, and tapering off posteriorly: disappearing as a separate
structure about the middle in length of the thoracic wall.


There is no indication of any bilateral arrangement of this
cellular tissue. The inner end of the clavicle and the costal
cartilages are composed of cartilage. The first three costal


cartilages join the cellular median sternum; the fourth and fifth A
There is no indication of any bilateral arrangement of this cellular tissue. The inner end of the clavicle and the costal cartilages are composed of cartilage. The first three costal cartilages join the cellular median sternum; the fourth and fifth A cartilages join those above them; the sixth and seventh have free pointed ends.


cartilages join those above them; the sixth and seventh have
free pointed ends.


In rat embryos of 9 mm. in length, a very similar condition
In rat embryos of 9 mm. in length, a very similar condition is found (figs. 2, 3. 4). In the angle between the jaw and the thoracic wall (praecervical sinus) there is a conglomeration in the middle line of mesoblastic cellular tissue; traceable laterally into association with the shoulder girdle, and concerned with the formation of the clavicles; thinning off as it passes backwards in the thoracic wall on the ventral aspect of the bulging heart.
is found (figs. 2, 3. 4). In the angle between the jaw and the


thoracic wall (praecervical sinus) there is a conglomeration


in the middle line of mesoblastic cellular tissue; ‘traceable
At this stage this cellular mass is not connected with any of the costal cartilages, which are extending in a ventral direction, and ending distally in tapering points (fig. 4). There is, moreover, no indication of bilateral subdivision of the mass, except at its cephalic end; there the cells are consolidated into two horns, which are concerned with the formation of the -clavicles and sterno-clavicular articulations, and with the an terior parts of the pre-sternum. , (b) In rat embryos, 10 mm. in length, an advance in develop ment has occurred (figs. 5-8). The sternum is still cellular. The pre-sternum is single and median (fig. 9), and at its cephalic end the component cells are more distinctly massed together on each side to produce the sterno-clavicular joints, and the inner ends of the clavicles. The cellular meso-sternum (figs. 10-12) consists of two definitely separate strands of mesoblastic cells, which are separated in the middle line by a layer of sparser and more loosely arranged cells. The cellular sternum is now joined by the first six costal cartilages (the seventh is still separate on each side), but there is an obvious distinction in the character of the cells composing sternum and costal cartilages (figs. 11, 12). The eighth costal cartilages are not in any way related to the sternum, and there is no indication of a meta-sternum.


1 Read at the Manchester meeting of the Anatomical Society of Great Britain
and Ireland,1900. '


In rat embryos, 13 mm. in length, the process of development has perceptibly advanced. Though the sternum is still cellular, and not yet converted into cartilage, the median separation between the two halves of the meso-sternum has disappeared, and the meso-sternum consists of a single median band of cellular tissue (fig. 14). The meta-sternum (fig. 15) has appeared; cellular in character, and tapering off in the angle between the chest wall and the diaphragm. The clavicle in its outer part is undergoing ossification, and its inner end is cartilaginous. It is clearly demarcated from the pre-sternum, although no joint cavity has yet appeared in the sterno-clavicular articulation (fig. 13). All the seven costal cartilages are now connected with the sternum; but there is still an obvious distinction between the character of the tissues composing the sternum on the one hand and the costal cartilages on the other (fig. 16).


laterally into association with the shoulder girdle, and concerned with the formation of the clavicles; thinning off as it
(c) The third stage in the development of the sternum is associated with the conversion of its cellular tissue into cartilage,—at first cellular, afterwards hyaline. The process begins in the pre-sternum in the upper lateral angles, along with the formation of the clavicle (fig. 11). In the mesosternum, cartilage cells first appear at the periphery of the band, in the intervals between the attachments of the costal cartilages (fig. 16). The parts of the sternumopposite the costal attachments remain longest in a cellular condition. In the meta-sternum, cartilage formation begins at the anterior end.  
passes backwards in the thoracic wall on the ventral aspect of
the bulging heart.


At this stage this cellular mass is not connected with any
Ultimately the sternum is laid down—a model of the future bone—as a simple median band of hyaline cartilage, separated at this stage from the clavicles by cellular connective tissue, but in complete fusion with the costal cartilages on each side, and presenting absolutely no differentiation of its component parts.
of the costal cartilages, which are extending in a ventral direction, and ending distally in tapering points (fig. 4). There is,
moreover, no indication of bilateral subdivision of the mass,
except at its cephalic end; there the cells are consolidated into
two horns, which are concerned with the formation of the


-clavicles and sterno-clavicular articulations, and with the an
Three human sterna of the third month, measuring respectively 8, 9, and 10 mm., show clearly this condition (figs. 17, 18, 19). The demarcation of sternal elements and of costal cartilages is shown in the special arrangements of the cartilage cells in lines, along which, later on, the joint cavities will be formed. In all three sterna the sterno-clavicular joint is completely formed, with its inter-articular fibro-cartilage. But in only one case is there a definite costo-sternal joint cavity (between the mesosternum and the right second costal cartilage) (fig. 18)}
terior parts of the pre-sternum. ,
(b) In rat embryos, 10 mm. in length, an advance in develop
ment has occurred (figs. 5-8). The sternum is still cellular. The
pre-sternum is single and median (fig. 9), and at its cephalic
end the component cells are more distinctly massed together
on each side to produce the sterno-clavicular joints, and the
inner ends of the clavicles. The cellular meso-sternum (figs.
10-12) consists of two definitely separate strands of mesoblastic


l cells, which are separated in the middle line by a layer of
(d) Thefurther changes in the cartilaginous sternum preceding ossification occur in rodents (rat, mouse) Without cleavage of the parts of the sternum or separation of costal cartilages. Opposite to the costal attachments the cartilage is distinctly hyaline, poorer in cells, and stained less deeply than in the intervals between the costal cartilages. In these intervals the cells are massed together, stain deeply, and the process of ossification is foreshadowed by the ‘formation of “ primary areolze,which occur in the centre of the pre-sternum, in the meta-sternum, and in the first four so-called segments of the meso-sternum (figs. 20, 21, 22).


sparser and more loosely arranged cells. The cellular sternum
is now joined by the first six costal cartilages (the seventh
is still separate on each side), but there is an obvious distinction in the character of the cells composing sternum and costal
cartilages (figs. 11, 12). The eighth costal cartilages are not in
any way related to the sternum, and there is no indication
of a meta-sternum.


In rat embryos, 13 mm. in length, the process of development has perceptibly advanced. Though the sternum is still
1 Figures 19 (A-J) show the existence of a sternal foramen. In several sections it presented the appearance of fissura sterni. The perforation contained vessels, one of which was of considerable size.
cellular, and not yet converted into cartilage, the median
separation between the two halves of the meso-sternum has
disappeared, and the meso-sternum consists of a single median
band of cellular tissue (fig. 14). The meta-sternum (fig. 15)
has appeared; cellular in character, and tapering off in the
angle between the chest wall and the diaphragm. The clavicle
in its outer part is undergoing ossification, and its inner end is
cartilaginous. It is clearly demarcated from the pre-sternum,
although no joint cavity has yet appeared in the sterno-clavicular
articulation (fig. 13). All the seven costal cartilages are now
THE STERNUM: ITS EARLY DEVELOPMENT AND OSSIFICATION. 23


connected with the sternum; but there is still an obvious
distinction between the character of the tissues composing
the sternum on the one hand and the costal cartilages on the
other (fig. 16).


(c) The third stage in the development of the sternum is
associated with the conversion of its cellular tissue into
cartilage,—at first cellular, afterwards hyaline. The process


begins in the pre-sternum in the upper lateral angles, along
These areolae increase in size, while at the same time the perichondrium becomes enormously thickened, followed by the formation of periosteal temporary bone in the usual way (fig. 22).


with the formation of the clavicle (fig. 11). In the mesosternum, cartilage cells first appear at the periphery of the
band, in the intervals between the attachments of the costal
cartilages (fig. 16). The parts of the sternumopposite the costal
attachments remain longest in a cellular condition. In the
meta-sternum, cartilage formation begins at the anterior end. .


Ultimately the sternum is laid down—a model of the future
Thus at birth (in the mouse, fig. 23), while there is complete fusion of the sternal elements together, and of the costal cartilages with them, there is a distinct differentiation of elements entering into the constitution of the sternum. Bone formation has begun, and cartilage only exists at the extremities"
bone—as a simple median band of hyaline cartilage, separated
of the pre-sternum and meta-sternum, in the meso-sternum opposite the costal attachments, and in the interval between the attachments of the sixth and seventh costal cartilages (fig. 24).
at this stage from the clavicles by cellular connective tissue,
but in complete fusion with the costal cartilages on each side,
and presenting absolutely no differentiation of its component
parts.


Three human sterna of the third month, measuring respectively 8, 9, and 10 mm., show clearly this condition (figs. 17, 18,
==II. Ossification==
19). The demarcation of sternal elements and of costal cartilages is shown in the special arrangements of the cartilage cells in
lines, along which, later on, the joint cavities will be formed. In
all three sterna the sterno-clavicular joint is completely formed,
with its inter-articular fibro-cartilage. But in only one case is
there a definite costo-sternal joint cavity (between the mesosternum and the right second costal cartilage) (fig. 18)}


(d) Thefurther changes in the cartilaginous sternum preceding ossification occur in rodents (rat, mouse) Without cleavage
The following facts have been derived from an examination of 236 sterna of human embryos between the foetal ages of three to nine months. 2
of the parts of the sternum or separation of costal cartilages.
Opposite to the costal attachments the cartilage is distinctly
hyaline, poorer in cells, and stained less deeply than in the
intervals between the costal cartilages. In these intervals the
cells are massed together, stain deeply, and the process of


1 Figures 19 (A-J) show the existence of a sternal foramen. In several
(A) Dates of oss7;ficat7'on.—The approximate periods of ossification in the component parts of the sternum are shown in Table I., which essentially corroborates the accepted account of the
sections it presented the appearance of fissura sterni. The perforation contained
vessels, one of which was of considerable size. ‘
24 PROFESSOR PATERSON.


ossification is foreshadowed by the ‘formation of “ primary
TABLE I.-—0ss*§fieatz'o-n, of the Ster-num (percentages).
areolze,” which occur in the centre of the pre-sternum, in the
meta-sternum, and in the first four so-called segments of the
meso-sternum (figs. 20, 21, 22).
 
These areolae increase in size, while at the same time the
perichondrium becomes enormously thickened, followed by the
formation of periosteal temporary bone in the usual way (fig. 22).
 
Thus at birth (in the mouse, fig. 23), while there is complete
fusion of the sternal elements together, and of the costal
cartilages with them, there is a distinct differentiation of
elements entering into the constitution of the sternum. Bone
 
formation has begun, and cartilage only exists at the extremities"
 
of the pre-sternum and meta-sternum, in the meso-sternum
opposite the costal attachments, and in the interval between the
attachments of the sixth and seventh costal cartilages (fig. 24).
 
II. OSSIFICATION.
 
The following facts have been derived from an examination
of 236 sterna of human embryos between the foetal ages of three
to nine months. 2


(A) Dates of oss7;ficat7'on.—The approximate periods of ossification in the component parts of the sternum are shown in Table
l CENTRE PRESENT. CENTRE ABSENT. I _ m 1 N Z l “J 2".“ as ‘6 0 , § Meso-sternum. g 2 E Meso-sternum. 2 ,3 Z :3 :5 E In E I-1 2 '25 2 5 . 2 ' -if - 2 $9 4 I ‘ Q 33 g <" E 1st 1 2nd 7 3rd 4th .3 5 1st 2nd 3rd 4th «E
I., which essentially corroborates the accepted account of the


TABLE I.-—0ss*§fieatz'o-n, of the Ster-num (percentages).
2 :5: 2
. mm. 1 1 IX. 122 64'4 96-7 99-2 99-2 2 83-3 29 , 8-1 3-3 3 -8 -8 16-6 71 91-8. VIII. 21 52-3- 81 81 1 76-2 47'6l 9-5i 14-3 l 19 19 23'8 52-3 90-5 85-7 I l VII. 16 49-1 93-3 87-5 3 87-5 62-5 37-5 12-5 6-6% 12-5 12-5 37-5 62-5| 87-5 VI. 3! 40'7 80'6 83'8 77'4 1 54'8 6'4 I 0 l9'3 16'1 22‘5 45'1 93'5 100 V. 7'4 36‘5 62'5 66'6 * 4I‘6 l2°5 4'1 l 0 37'5 33'3 58’3 87'5 958 100 IV. 1 29'6 15'3 23 15'3 7'7 H 77 1 0 84'6 77 8-1'6 92'3 92'3 100 III. ; 23'9 2'2 2'2 2‘2 , 1'1 1 0 0 77'7 77'7 77'7 88'8 100 100 a 4 ,


l
CENTRE PRESENT. CENTRE ABSENT.
I _ m  1 N Z l “J 2".“
as  ‘6 0 , § Meso-sternum. g 2 E Meso-sternum. 2
,3 Z :3 :5  E In E I-1
2 '25 2 5 . 2 ' -if - 2 $9
4 I ‘ Q
33 g <" E 1st 1 2nd 7 3rd 4th .3 5 1st 2nd 3rd 4th «E
* 2 :5: 2
. mm. 1 1
IX. 122 64'4 96-7 99-2  99-2 2 83-3 29 , 8-1 3-3 3 -8 -8 16-6 71 91-8.
VIII. 21 52-3- 81 81 1 76-2 47'6l 9-5i 14-3 l 19 19 23'8 52-3 90-5 85-7
I l
VII. 16 49-1 93-3 87-5 3 87-5 62-5 37-5 12-5 6-6% 12-5 12-5 37-5 62-5| 87-5
VI. 3! 40'7 80'6 83'8 77'4 1 54'8 6'4 I 0 l9'3 16'1 22‘5 45'1 93'5 100
V. 7'4 36‘5 62'5 66'6 * 4I‘6 l2°5 4'1 l 0 37'5 33'3 58’3 87'5 958 100
IV.  1 29'6 15'3 23 15'3 7'7 H 77 1 0 84'6 77 8-1'6 92'3 92'3 100
III. ; 23'9 2'2 2'2 2‘2 , 1'1 1 0 0 77'7 77'7 77'7 88'8 100 100
a 4 ,


.
dates at which the several centres appear. The first nuclei appear generally in the sixth month for the pre-sternum and the first piece of the meso-sternum. In the seventh month centres appear for the second and third pieces of the mesosternum. N 0 further addition to the number of centres occurs during the eighth and ninth months ; and in full-time foetuses (of which 122 examples were examined) the fourth piece of the meso-sternum and the meta-sternum are usually cartilaginous. (B) Position and number of centres of osmfication.-—In Table II. a summary is given of the situation and number of centres of ossification in the component parts of the sternum. A more intimate analysis did not appear necessary; and for the sake of brevity and clearness, reference has been omitted to the separation or fusion of double centres, and to obliquity in their position (such oblique double nodules being grouped as lateral). The results tabulated, it should be noted, are reached from an examination of specimens of which the large majority are fulltime foetuses. The cases of younger sterna are not only fewer in number, but are also less advanced in ossification.


~-—u. .
THE STERNUM: ITS EARLY DEVELOPMENT AND OSSIFICATION. 25


dates at which the several centres appear. The first nuclei
While there is considerable variability both in number and position, the centres of ossification are, as a general rule, single and median, and are six in number; one for the pre-sternum, one each for the first four elements of the meso-sternum, and one for the meta-sternum. Exceptions to this rule are found in all situations except in the meta-sternum, which in the few cases in which bone formation has begun, is invariably provided with a single median centre.
appear generally in the sixth month for the pre-sternum and
the first piece of the meso-sternum. In the seventh month
centres appear for the second and third pieces of the mesosternum. N 0 further addition to the number of centres occurs
during the eighth and ninth months ; and in full-time foetuses
(of which 122 examples were examined) the fourth piece of the
meso-sternum and the meta-sternum are usually cartilaginous.
(B) Position and number of centres of osmfication.-—In Table
II. a summary is given of the situation and number of centres
of ossification in the component parts of the sternum. A more
intimate analysis did not appear necessary; and for the sake of
brevity and clearness, reference has been omitted to the


separation or fusion of double centres, and to obliquity in their
The pre—sternum is generally formed by a single centre (79 per cent.). When there are two centres, they are generally vertica.1ly placed. Three or more centres occur quite rarely (26 per cent.).


position (such oblique double nodules being grouped as lateral).
The first centre for the meso-sternum is, as a rule, also single (785 per cent.); when there are two, they are usually laterally placed. The second and third centres of the meso-sternum are less frequently single than the above-named centres (593 per cent.: 60'5 per cent.). When there are two centres, they are in most cases laterally placed. The fourth centre in the mesosternum is not generally present. When it occurs it is nearly as often double ‘as single; and when two centres are present, they are as often vertical as lateral in position.  
The results tabulated, it should be noted, are reached from an
examination of specimens of which the large majority are fulltime foetuses. The cases of younger sterna are not only fewer
in number, but are also less advanced in ossification.


While there is considerable variability both in number and
position, the centres of ossification are, as a general rule, single
and median, and are six in number; one for the pre-sternum,
one each for the first four elements of the meso-sternum, and
one for the meta-sternum. Exceptions to this rule are found in
all situations except in the meta-sternum, which in the few
cases in which bone formation has begun, is invariably provided
with a single median centre.


The pre—sternum is generally formed by a single centre (79
per cent.). When there are two centres, they are generally
vertica.1ly placed. Three or more centres occur quite rarely
(26 per cent.).
The first centre for the meso-sternum is, as a rule, also single
(785 per cent.); when there are two, they are usually laterally
placed. The second and third centres of the meso-sternum are
less frequently single than the above-named centres (593 per
cent.: 60'5 per cent.). When there are two centres, they are
in most cases laterally placed. The fourth centre in the mesosternum is not generally present. When it occurs it is nearly
as often double ‘as single; and when two centres are present,
they are as often vertical as lateral in position.
TABLE II.-—-Median and Lateral Ossvgficcttion.
TABLE II.-—-Median and Lateral Ossvgficcttion.


Line 241: Line 82:
5 1 —-L -r ‘ocunj -1:-T .-:——j-—::
5 1 —-L -r ‘ocunj -1:-T .-:——j-—::


14 }9 1 24 3}12
14 }9 1 24 3}12 3 4 1 3
3 4 1 3


1 0} 3 '0 4 0} } 0 }
1 0} 3 '0 4 0} } 0 }


I27 0 3 }5 .0 1 0 3
I27 0 3 }5 .0 1 0 3 17 25 ' 15
17 25 ' 15
 




I
I i I
i
I


Centre Single, . . _ . . 84
Centre Single, . . _ . . 84 » Double X::~':::::," : 23 }2s ,, Three or more, . . 4
» Double X::~':::::," : 23 }2s
,, Three or more, . . 4


1.
1.
Line 265: Line 100:
147 179
147 179


3g}3: }39   l 209
3g}3: }39 l 209


<1 —¢14—
<1 —¢14—
Line 273: Line 108:
78'5
78'5


5 147 2 6 ..
5 147 2 6 .. 30 }35 16.0} 186 _
30 }35 16.0} 186 _


5}4o 2.6 21 3
5}4o 2.6 21 3
Line 280: Line 114:
137 ,.. ..
137 ,.. ..


7 108 ] 3_8.. 59-3
7 108 ] 3_8.. 59-3 b.:}74 33 }3::: 40-6
b.:}74 33 }3::: 40-6


-Lee-nj-——— u--——-—
-Lee-nj-——— u--——-—


182 . . . .
182 . . . . l 60-5
l 60-5


5 3-5 "
5 3-5 " 42 } 47 -29-5} 33 . 9}56 6.3 39 3
42 } 47 -29-5} 33 .
9}56 6.3 39 3


Pre-sternum.
Pre-sternum.


O
O rJ"~. 00
rJ"~.
00


7*:
7*: CO
CO


1
1 Total Ossified , . . . . 111 g
Total Ossified , . . . . 111 g


Centre Single, . . _ . .
Centre Single, . . _ . . Meso-sternum. Double Vertncal, .
Meso-sternum. Double Vertncal, .


so 15 0 12 1 2 12
so 15 0 12 1 2 12 1 1 FirstPiece. » Lateral, . 25}25}30,1} 2}2 1}1}2 2} 3}3 1} 3}3 4 o 1 o no 17 — 15
1 1
FirstPiece. » Lateral, . 25}25}30,1} 2}2 1}1}2 2} 3}3 1} 3}3
4 o 1 o
no 17 — 15


,, Three or more, . .
,, Three or more, . .
Line 321: Line 142:
Total ossined, . . . .
Total ossined, . . . .


 
Centre Single, . V .ti . 5 59 0 12 1] 9 #1 0 5
Centre Single, . V .ti . 5 59 0 12 1] 9 #1 0 5


- er ca .
- er ca .


SecondP1ece. ,, Double Lateral,’ _ 47}52 4} 4}4 I 31 «i}5 4} 5}5 1} (1)}1
SecondP1ece. ,, Double Lateral,’ _ 47}52 4} 4}4 I 31 «i}5 4} 5}5 1} (1)}1 _ 14 __
_ 14 __


61!-(O
61!-(O r-’% Q1-I
r-’%
Q1-I


,, Three or more, . . 6} 58 0
,, Three or more, . . 6} 58 0
Line 338: Line 155:
1-__.—. T — en;
1-__.—. T — en;


N963 (N
N963 (N I 1-! 24% b
I
1-!
24%
b


I O9
I O9
Line 350: Line 163:
Centre Single, . . . 59 7 4 14 1
Centre Single, . . . 59 7 4 14 1


Third Piece. ,, Double ; 33}33}41 g} 3}3 5}6 ‘ g} 3}3 i (1, 1}_l
Third Piece. ,, Double ; 33}33}41 g} 3}3 5}6 ‘ g} 3}3 i (1, 1}_l ,, Three or more, . . 8 1
,, Three or more, . . 8 1


Q1
Q1 55% r"’% CW
55%
r"’%
CW


.. 5- — :3. -2- an. - ——
.. 5- — :3. -2- an. - ——
Line 362: Line 171:
Total Ossifled, . . . . 100 10 , 10 ‘ 17 2
Total Ossifled, . . . . 100 10 , 10 ‘ 17 2


Centre Single, .{v .t_ . 7 18 0 1 I 2 3 1 0
Centre Single, .{v .t_ . 7 18 0 1 I 2 3 1 0 th P’ . - "'°‘‘ ° }14 1 } 3 1 } 1 Four 1ece ,, Double ‘Lateral,’ . 7 }u 1 }1 1 }3 1 }1 0 0}1 .1..- .
th P’ . - "'°‘‘ ° }14 1 } 3 1 } 1
Four 1ece ,, Double ‘Lateral,’ . 7 }u 1 }1 1 }3 1 }1 0 0}1
.1..- .


ONOCN
ONOCN


N
N 9% 6061930 9% ON
9%
6061930
9%
ON


,, Three or more, . . 0
,, Three or more, . . 0
Line 381: Line 183:
Total Ossified, . . . . 32 2 i 6 .1
Total Ossified, . . . . 32 2 i 6 .1


|HOOOfiH|OOOO cl o
|HOOOfiH|OOOO cl o I l I O
I
l I O


Meta-sternum. Single Centre, .' . . . 10 3 2 V 1 1
Meta-sternum. Single Centre, .' . . . 10 3 2 V 1 1


26


PROFESSOR PATERSON.
The part of the sternum between the attachments of the sixth and seventh costal cartilages is cartilaginous at birth, and the question of its ossification is deferred for the present. It appears that it may be ossified by extension from the fourth piece, though there is reason for believing that in some cases at least it may possess a separate and independent centre.
‘THE STERNUM: ITS EARLY DEVELOPMENT AND OSSIFICATION. 27
 
(0) Fissures: Grooves: Fomm6'na.—One remarkable negative feature characterises the series of foetal sterna examined. In all there is a complete median plate of cartilage, grooved it may be . on one or both sides, perforated in some instances by one or
 
more holes, but in no single instance is there a fissum storm; A longitudinal groove (Table III.) is characteristic of the foetal
 
TABLE III.—Grooves.
 
1' Per Cent. I Months. , lases. Present. Absent.
 
Present. Absent. '
l IX. 113 75 38 66-3 I 336 1' VIII. 17 6 11 35'2 6467 I VII. 16 13 3 ' 812 18'?


The part of the sternum between the attachments of the sixth
2 VI. 30 24 6 80-0 20-0
and seventh costal cartilages is cartilaginous at birth, and the
V. 24 19 5 79'1 208 IV. A 13 13 0 100 III. 9 8 1 88'8 ll°l Total 222 158 a 64 70'1 29'0 1
question of its ossification is deferred for the present. It
appears that it may be ossified by extension from the fourth
piece, though there is reason for believing that in some cases at
least it may possess a separate and independent centre.


(0) Fissures: Grooves: Fomm6'na.—One remarkable negative
meso-sternum, occurring in 158 out of 222 examples, or 7 0'1 per -cent., a proportion which obtains generally for all ages. It may be faint or obvious ; it may be found on one or both aspects of the meso-sternum, and implicate it in the whole or part of its length, but it never appears in the pre-sternum. This grooving of the meso-sternum is probably associated with the method of early development of the cartilage, but it is at the same time plain that it is not necessarily coincident with a bilateral asymcation of the meso-sternum.
feature characterises the series of foetal sterna examined. In
all there is a complete median plate of cartilage, grooved it may
be . on one or both sides, perforated in some instances by one or


more holes, but in no single instance is there a fissum storm;
A longitudinal groove (Table III.) is characteristic of the foetal


TABLE III.—Groo'ves.


1' Per Cent.
I Months. , lases. Present. Absent.
* Present. Absent. '
l IX. 113 75 38 66-3 I 336
1' VIII. 17 6 11 35'2 6467
I VII. 16  13 3 ' 812 18'?
2 VI. 30 24 6 80-0 20-0
V. 24 19 5 79'1 208
IV. A 13 13 0 100
III. 9 8 1 88'8 ll°l
Total 222 158 a 64 70'1 29'0 1


meso-sternum, occurring in 158 out of 222 examples, or 7 0'1 per
-cent., a proportion which obtains generally for all ages. It may
be faint or obvious ; it may be found on one or both aspects of
the meso-sternum, and implicate it in the whole or part of its
length, but it never appears in the pre-sternum. This grooving
of the meso-sternum is probably associated with the method of
TABLE IV.—Stemal Fommina.
TABLE IV.—Stemal Fommina.


Line 433: Line 215:
PRESENT.
PRESENT.


ABSENT. . . . r more
ABSENT. . . . r more N°- One 1n Two In One 1n TWO 0
N°- One 1n Two In One 1n TWO 0


M°nth3- » °f - Meta-sternum Meta-sternum Meso-sternum in Lfisfigiand TOTAI“
M°nth3- » °f - Meta-sternum Meta-sternum Meso-sternum in Lfisfigiand TOTAI“ e . ,
e . ,


Per
Per
Line 449: Line 229:
cent. cent.
cent. cent.


I Per
I Per No. cent. No.
No. cent. No.


.00
.00


IX. .120 81 67'5 23  
IX. .120 81 67'5 23 VIII. 2o 14 70
VIII. 2o 14 70


VII. 16 10 62-5
VII. 16 10 62-5
Line 461: Line 239:
VI. 30 20 66'6
VI. 30 20 66'6


I
I
 
Present :H 1 in meta-sternum
Present :H 1 in meta-sternum
2 in meta-sternum
2 in meta-sternum
1 in meso-sternum 2 or more in mesosternum and meta 2 sternum 0
1 in meso-sternum
2 or more in mesosternum and meta 2 sternum
0


Absent . . . 164 = 69 '4 per cent.
Absent . . . 164 = 69 '4 per cent.
Line 473: Line 248:
u-100
u-100


moo
moo II II II
II II II


IV. 13 7 53 '9 5
IV. 13 7 53 '9 5
Line 482: Line 256:
.;:e—-———:u-:a-j-T1-ajjj.-———-——.———-——:——jo
.;:e—-———:u-:a-j-T1-ajjj.-———-——.———-——:——jo


Total present 7;=30‘5 per cent.
Total present 7;=30‘5 per cent.


 


V0
V0
Line 502: Line 275:
to H O O O v-I O 00
to H O O O v-I O 00




28


PROFESSOR PATERSON.
THE STERNUM: ITS EARLY DEVELOPMENT AND OSSIFICATION. 29


early development of the cartilage, but it is at the same time
Sternal foramina (Table IV.) occur only occasionally (in 72 out of 236 cases, or 30'5 per cent.). The number and situation of the perforations are as follows :— 9
plain that it is not necessarily coincident with a bilateral asymcation of the meso-sternum.


Sternal foramina (Table IV.) occur only occasionally (in 72
Cases. ’ Per cent.
out of 236 cases, or 30'5 per cent.). The number and situation
of the perforations are as follows :— 9


Cases. ’ Per cent.
One foramen in the meta-sternum . . . 54 22'8 Two foramina in the meta-sternum . ' . 5 2'1 One foramen in the meso-sternum . . . 8 3'3


One foramen in the meta-sternum . . . 54  22'8
Two or more foramina (in the meso-sternum and meta-sternum) . . . . . 5 2'1 7 2 . . . 30'5
Two foramina in the meta-sternum . ' . 5 2'1
One foramen in the meso-sternum . . . 8  3'3


Two or more foramina (in the meso-sternum
The great majority thus occur singly in the meta-sternum, and the pre-sternum is never perforated. From an examination of a human embryonic sternum 9 mm. in length (third month) (fig. 19), one is led to believe that the perforation is due to the persistence of vessels, preventing the conversion of the embryonic connective tissue into cartilage in the middle line.
and meta-sternum) . . . . . 5  2'1
7 2 . . . 30'5


The great majority thus occur singly in the meta-sternum, and
Like the grooves, these foramina are not improbably causally associated with the mode of early development of the sternum, and it is therefore noteworthy that neither grooves nor foramina occur in the pre-sternum.
the pre-sternum is never perforated. From an examination
of a human embryonic sternum 9 mm. in length (third month)
(fig. 19), one is led to believe that the perforation is due to the
persistence of vessels, preventing the conversion of the embryonic connective tissue into cartilage in the middle line.


Like the grooves, these foramina are not improbably causally
(D) Union of sternal elements and costal ea'rtz'lages.—An examination of the mode of union of the parts of the sternum with one another and with the costal cartilages brings out the fact that the connections are much the same in the earlier and later months of foetal life (Table V.).
associated with the mode of early development of the sternum,
and it is therefore noteworthy that neither grooves nor foramina
occur in the pre-sternum.


(D) Union of sternal elements and costal ea'rtz'lages.—An
The pre-sternum and meso-sternum are usually connected together by a fibrous lamina (764 per cent.) opposite the attachments of the second costal cartilages. More rarely they are fused together by cartilaginous union (23'6 per cent.). I have only met with one example (in a 9 months foetus) of a case of alteration in position of the junction to the point opposite the attachments of the third costal cartilages.
examination of the mode of union of the parts of the sternum
with one another and with the costal cartilages brings out the
fact that the connections are much the same in the earlier and
later months of foetal life (Table V.).


The pre-sternum and meso-sternum are usually connected
The meso-sternum and meta-sternum are usually (77°9 per cent.) united by cartilage, and only exceptionally (221 per cent.) by a fibrous lamina.
together by a fibrous lamina (764 per cent.) opposite the attachments of the second costal cartilages. More rarely they are
fused together by cartilaginous union (23'6 per cent.). I have
only met with one example (in a 9 months foetus) of a case of
alteration in position of the junction to the point opposite the
attachments of the third costal cartilages.


The meso-sternum and meta-sternum are usually (77°9 per
The costal cartilages in the centre of the series are generally 30 PROFESSOR PATERSON.
cent.) united by cartilage, and only exceptionally (221 per cent.)
by a fibrous lamina.


The costal cartilages in the centre of the series are generally
fused with the lateral borders of the sternum, and are not united to it by a. fibrous lamina. The first costal cartilage is also, as a rule (813 per cent.) continuous with the pre-sternum. Occasionally on one side or both the union is fibrous.
30 PROFESSOR PATERSON.


fused with the lateral borders of the sternum, and are not united
The condition of the seventh and eighth costal cartilages has been particularly noted. It is not uncommon for the pair of seventh cartilages to articulate together in front of the sternum (34 cases—14°4 per cent.). (In still fewer cases the same occurs
to it by a. fibrous lamina. The first costal cartilage is also, as a
rule (813 per cent.) continuous with the pre-sternum. Occasionally on one side or both the union is fibrous.


The condition of the seventh and eighth costal cartilages has
been particularly noted. It is not uncommon for the pair of
seventh cartilages to articulate together in front of the sternum
(34 cases—14°4 per cent.). (In still fewer cases the same occurs


TABLE V.——7S'epamt'i0n of Ste’/mal Elements and Costal
TABLE V.——7S'epamt'i0n of Ste’/mal Elements and Costal




0a~rtt'lage3.
_ - ‘ 3
Months . . . . . . IX. VIII. VII. VI. v. IV. III. 01;;
. "" ’ -"'" ' '__’ T 1- '—""' -"—' '"-" ""_"
Prggiggnfifm {Fibrous . . . I 75-1 73-9 99-9 37 583 69-2 66-6 =76-4 F
Mesojsggrnumj Cartilaginous . . 24-7 21 O . 12-9 41-6 36-7 33-3 =23'6
Meggggrggm Fibrous . . . 31 31-5 31-2 46 9 6 11-1 =22-1 1
Memgfigmum Cartilaginous . . J 63-9 63-4 63-7 66 96-9 166 33-3 =77-9 V
Fibrous . . . I 14 25 6'6 0 0 153 111
Fggftflgzgal Cartilaginous . . 76 63-7 80 100 73-2 76-9 33-3 =31-3
Dissimilar . . . 9'9 187 133 0 21°6 7'6 0
Sgvepflh {Separate from sternum 6'6 5'8 18 '7 15-3 0 9 0 :92
OS
Cartilage United . . . 93-4 94-2 31-3 34-7 100 91 166 = 3
Eighth costal Separate from sternum 90 100 100 967 100 909 88°8 =95'2 ‘
Cartilage United . . . 99 0 6 3-5 6 9 11-1 = 4-3


1- 4-} r if r I I
0a~rtt'lage3. _ - ‘ 3 Months . . . . . . IX. VIII. VII. VI. v. IV. III. 01;; . "" ’ -"'" ' '__’ T 1- '—""' -"—' '"-" ""_" Prggiggnfifm {Fibrous . . . I 75-1 73-9 99-9 37 583 69-2 66-6 =76-4 F Mesojsggrnumj Cartilaginous . . 24-7 21 O . 12-9 41-6 36-7 33-3 =23'6 Meggggrggm Fibrous . . . 31 31-5 31-2 46 9 6 11-1 =22-1 1 Memgfigmum Cartilaginous . . J 63-9 63-4 63-7 66 96-9 166 33-3 =77-9 V Fibrous . . . I 14 25 6'6 0 0 153 111 Fggftflgzgal Cartilaginous . . 76 63-7 80 100 73-2 76-9 33-3 =31-3 Dissimilar . . . 9'9 187 133 0 21°6 7'6 0 Sgvepflh {Separate from sternum 6'6 5'8 18 '7 15-3 0 9 0 :92 OS Cartilage United . . . 93-4 94-2 31-3 34-7 100 91 166 = 3 Eighth costal Separate from sternum 90 100 100 967 100 909 88°8 =95'2 ‘ Cartilage United . . . 99 0 6 3-5 6 9 11-1 = 4-3
with the sixth costal cartilage.) In 8 per cent. of the cases the
seventh cartilage fails to reach the sternum on one side or both.
On the other hand, the eighth cartilage on one side or both is
connected with the sternum in still fewer cases (48 per cent.).
In rare cases, the 5th, 6th, or 7th cartilage reaches on one side
to the middle line of the sternum, its distal end pushing its way
forwards through the body of the sternum.


(E) Shape of the meta-ste7°num.—Out of 189 cases, the metasternum is present in 182 (963 per cent.); absent in seven
1- 4-} r if r I I with the sixth costal cartilage.) In 8 per cent. of the cases the seventh cartilage fails to reach the sternum on one side or both. On the other hand, the eighth cartilage on one side or both is connected with the sternum in still fewer cases (48 per cent.). In rare cases, the 5th, 6th, or 7th cartilage reaches on one side to the middle line of the sternum, its distal end pushing its way forwards through the body of the sternum.
instances (37 per cent.). I have been as careful as possible to
discard all examples in which there was the slightest indication that the meta-sternum had been accidentally lost in


maceration.
(E) Shape of the meta-ste7°num.—Out of 189 cases, the metasternum is present in 182 (963 per cent.); absent in seven instances (37 per cent.). I have been as careful as possible to discard all examples in which there was the slightest indication that the meta-sternum had been accidentally lost in maceration.  
THE STERNUM: ITS ‘EARLY DEVELOPMENT AND OSSIFICATION. 31


While the shape is extremely variable, it is more often single
While the shape is extremely variable, it is more often single and median than bifurcated. An undivided meta-sternum occurs in 107 cases (57 '6 per cent.); a bifid meta-sternum in 77 cases (423 per cent.).
and median than bifurcated. An undivided meta-sternum
occurs in 107 cases (57 '6 per cent.); a bifid meta-sternum in
77 cases (423 per cent.).


(F) Anomalz'es—-epi-sternal cart2Ilages.—One of the most striking features of the series of embryonic sterna examined is the
(F) Anomalz'es—-epi-sternal cart2Ilages.—One of the most striking features of the series of embryonic sterna examined is the absence of anomalous conditions, and the regularity and symmetry of development. N 0 case of fissum sterml is recorded. One example occurs of transference of the pre-meso-sternal junction to the level of the third costal cartilages. A few instances are found in which one or more costal cartilages (usually the 5th, 6th, or 7th) force their way through the cartilaginous sternum to the middle line. Absence of the meta-sternum, asymmetry in the attachment of costal cartilages, and fusion of contiguous costal cartilages together, also occurred in a few examples.
absence of anomalous conditions, and the regularity and symmetry of development. N 0 case of fissum sterml is recorded.
One example occurs of transference of the pre-meso-sternal
junction to the level of the third costal cartilages. A few
instances are found in which one or more costal cartilages
(usually the 5th, 6th, or 7th) force their way through the
cartilaginous sternum to the middle line. Absence of the
meta-sternum, asymmetry in the attachment of costal cartilages, and fusion of contiguous costal cartilages together, also
occurred in a few examples.


Epi-sterna! ca7~t'ilages.—-I11 two cases supra-sternal cartilages
Epi-sterna! ca7~t'ilages.—-I11 two cases supra-sternal cartilages have been found, situated at the cephalic border of the presternum, between the clavicular articular surfaces. In one case the cartilages are separated from the pre-sternum and fused together; in the other case, they are separate from one another, but continuous with the cartilaginous pre-sternum.
have been found, situated at the cephalic border of the presternum, between the clavicular articular surfaces. In one case
the cartilages are separated from the pre-sternum and fused
together; in the other case, they are separate from one another,
but continuous with the cartilaginous pre-sternum.


It is not my desire to make any general deductions, or attempt
It is not my desire to make any general deductions, or attempt to draw any definite conclusions from these observations at present. The subject is a large one, and is only very partially dealt with in this communication. I have ventured to make this bare statement of fact to the Anatomical Society, partly in order to clear the way for further work on the same subject, and partly to draw attention to some of the general morphological problems associated with a study of the human and mammalian sternum.
to draw any definite conclusions from these observations at
present. The subject is a large one, and is only very partially
dealt with in this communication. I have ventured to make
this bare statement of fact to the Anatomical Society, partly in
order to clear the way for further work on the same subject, and
partly to draw attention to some of the general morphological


problems associated with a study of the human and mammalian
sternum. '


[Dnsoarprron
==Description Of Plates==
32 THE STERNUM: ITS EARLY DEVELOPMENT AND OSSIFICATION.
 
DESCRIPTION OF PLATES II., III.


Fig. 1. Human embryo (sagittal section).
Fig. 1. Human embryo (sagittal section).
Line 646: Line 330:
Fig. 3. ,, ,, Sagittal section through chest wall.
Fig. 3. ,, ,, Sagittal section through chest wall.


Fig. 4. ,, ,, Transverse section through middle of chest
Fig. 4. ,, ,, Transverse section through middle of chest wall, showing ossifying ribs and absence of sternum.
wall, showing ossifying ribs and absence
of sternum.


gig‘ Rat 10 mm’ 1 Magnified seven times, showing clavicles,
gig‘ Rat 10 mm’ 1 Magnified seven times, showing clavicles,
 
7' ” ” }- pregslizernum, meso-sternum, and costal


7' ” ” }- pregslizernum, meso-sternum, and costal
. ' ' ” 1 ” car 1 ages.
. ' ' ” 1 ” car 1 ages.


Fig. 8. ,, ,,
Fig. 8. ,, ,,


9' Rat 10 mm’ acteristic features of pre-sternum and
9' Rat 10 mm’ acteristic features of pre-sternum and
Fig’ 10' ” ” meso-sternum.
Fig’ 10' ” ” meso-sternum.


Fig. 11. Bat 10 mm. { Higher magnification, to show differentiation
Fig. 11. Bat 10 mm. { Higher magnification, to show differentiation Fig. 12. ,, ,, of tissue in sternum and costal cartilages.
Fig. 12. ,, ,, of tissue in sternum and costal cartilages.


{ Magnified twenty-eight times, to show char
{ Magnified twenty-eight times, to show char
  Rat 13 mm’  Magnified seven times, to show structure and
Fig’ 15' ” ” , connections of sternal elements.
' ' 3! 3)


{ Magnified twenty—eight times, to show general
Rat 13 mm’  Magnified seven times, to show structure and
Fig. 16. Rat .13 mm. structure of sternum and connections of
Fig’ 15' ” ” , connections of sternal elements. ' ' 3! 3)
' costal cartilages.
 
{ Magnified twenty—eight times, to show general Fig. 16. Rat .13 mm. structure of sternum and connections of ' costal cartilages.


Fig. 17. Human sternum, 3rd month, 8 mm. long, magnified twentyeight times.
Fig. 17. Human sternum, 3rd month, 8 mm. long, magnified twentyeight times.
Line 677: Line 355:
Fig. 18. Human sternum, 3rd month, 10 mm. long, magnified twentyone times.
Fig. 18. Human sternum, 3rd month, 10 mm. long, magnified twentyone times.


Fig. 19. A-I. Sections of human sternum, 3rd month, 9 mm. long,
Fig. 19. A-I. Sections of human sternum, 3rd month, 9 mm. long, possessing sternal foramen and 8 costal carti1ages,—-magnified 18 times. J. Reconstruction of same.
possessing sternal foramen and 8 costal carti1ages,—-magnified 18 times.
J. Reconstruction of same.
 
Fig. 20. Rat embryo. Coronal section of cartilaginous sternum,
showing primary areolae,—magnified seven times.


Fig. 21. Coronal section of older rat’s sternum, showing primary
Fig. 20. Rat embryo. Coronal section of cartilaginous sternum, showing primary areolae,—magnified seven times.
areolae and absence of ossification in last piece of mcso-sternum,-—
magnified seven times. I


Fig. 22. Coronal section of older rat’s sternum, showing primary
Fig. 21. Coronal section of older rat’s sternum, showing primary areolae and absence of ossification in last piece of mcso-sternum,-— magnified seven times. I
areolae, thickened perichondrium, and absence of bone formation between 6th and 7th costal cartilages. ,


Fig. 23. Coronal section of sternum of mouse a few days after birth,
Fig. 22. Coronal section of older rat’s sternum, showing primary areolae, thickened perichondrium, and absence of bone formation between 6th and 7th costal cartilages. ,
showing bone formation and cartilages.


Fig. 24. Sternum (lower end) of rat 9 days old, showing ossification.
Fig. 23. Coronal section of sternum of mouse a few days after birth, showing bone formation and cartilages.
./our/2. o/‘Anal. cal’/zy.s‘. Oct . /900.:


15' a’ ma W/7502:,/1'//2. Cam br/'a’_qe
Fig. 24. Sternum (lower end) of rat 9 days old, showing ossification. ./our/2. o/‘Anal. cal’/zy.s‘. Oct . /900.:
../ou/5/1.0/'/Irzart. &Pfiy.s*. Uct. 7900.


15' a’ ma W/7502:,/1'//2. Cam br/'a’_qe ../ou/5/1.0/'/Irzart. &Pfiy.s*. Uct. 7900.


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Paterson The sternum - its early development and ossification in man and mammals. (1900) J Anat Physiol. 35(1): 21-32 PMID 17232454

The Sternum - Its Early Development and Ossification in Man and Mammals

By Professor Paterson (1900)

Liverpool. (PLATES II., III.)

(Preliminary Communication).

  • Read at the Manchester meeting of the Anatomical Society of Great Britain and Ireland,1900.


In the following pages the record is given of some recent observations upon the early development and ossification of the sternum in man and certain mammals (chiefly rodents). The morphological problems associated with the anatomy and development of this bone are so numerous and important, that it has seemed desirable to make, in the first place, a brief statement of certain facts of development, so as to clear the way for future discussion and consideration of the more general anatomical questions in which the sternum is implicated.

I. Early Development

The following observations upon the early development of the sternum were made on rat and human embryos.

(at) In a series of continuous sagittal sections through aihuman embryo in the second month, prepared and placed at my disposal by Professor Paul, the first anlage of the sternum (fig. 1) is to be seen as a dense conglomeration of mesoblastic cells, occupying the anterior part of the thoracic wall in the middle line, and tapering off posteriorly: disappearing as a separate structure about the middle in length of the thoracic wall.


There is no indication of any bilateral arrangement of this cellular tissue. The inner end of the clavicle and the costal cartilages are composed of cartilage. The first three costal cartilages join the cellular median sternum; the fourth and fifth A cartilages join those above them; the sixth and seventh have free pointed ends.


In rat embryos of 9 mm. in length, a very similar condition is found (figs. 2, 3. 4). In the angle between the jaw and the thoracic wall (praecervical sinus) there is a conglomeration in the middle line of mesoblastic cellular tissue; traceable laterally into association with the shoulder girdle, and concerned with the formation of the clavicles; thinning off as it passes backwards in the thoracic wall on the ventral aspect of the bulging heart.


At this stage this cellular mass is not connected with any of the costal cartilages, which are extending in a ventral direction, and ending distally in tapering points (fig. 4). There is, moreover, no indication of bilateral subdivision of the mass, except at its cephalic end; there the cells are consolidated into two horns, which are concerned with the formation of the -clavicles and sterno-clavicular articulations, and with the an terior parts of the pre-sternum. , (b) In rat embryos, 10 mm. in length, an advance in develop ment has occurred (figs. 5-8). The sternum is still cellular. The pre-sternum is single and median (fig. 9), and at its cephalic end the component cells are more distinctly massed together on each side to produce the sterno-clavicular joints, and the inner ends of the clavicles. The cellular meso-sternum (figs. 10-12) consists of two definitely separate strands of mesoblastic cells, which are separated in the middle line by a layer of sparser and more loosely arranged cells. The cellular sternum is now joined by the first six costal cartilages (the seventh is still separate on each side), but there is an obvious distinction in the character of the cells composing sternum and costal cartilages (figs. 11, 12). The eighth costal cartilages are not in any way related to the sternum, and there is no indication of a meta-sternum.


In rat embryos, 13 mm. in length, the process of development has perceptibly advanced. Though the sternum is still cellular, and not yet converted into cartilage, the median separation between the two halves of the meso-sternum has disappeared, and the meso-sternum consists of a single median band of cellular tissue (fig. 14). The meta-sternum (fig. 15) has appeared; cellular in character, and tapering off in the angle between the chest wall and the diaphragm. The clavicle in its outer part is undergoing ossification, and its inner end is cartilaginous. It is clearly demarcated from the pre-sternum, although no joint cavity has yet appeared in the sterno-clavicular articulation (fig. 13). All the seven costal cartilages are now connected with the sternum; but there is still an obvious distinction between the character of the tissues composing the sternum on the one hand and the costal cartilages on the other (fig. 16).

(c) The third stage in the development of the sternum is associated with the conversion of its cellular tissue into cartilage,—at first cellular, afterwards hyaline. The process begins in the pre-sternum in the upper lateral angles, along with the formation of the clavicle (fig. 11). In the mesosternum, cartilage cells first appear at the periphery of the band, in the intervals between the attachments of the costal cartilages (fig. 16). The parts of the sternumopposite the costal attachments remain longest in a cellular condition. In the meta-sternum, cartilage formation begins at the anterior end.

Ultimately the sternum is laid down—a model of the future bone—as a simple median band of hyaline cartilage, separated at this stage from the clavicles by cellular connective tissue, but in complete fusion with the costal cartilages on each side, and presenting absolutely no differentiation of its component parts.

Three human sterna of the third month, measuring respectively 8, 9, and 10 mm., show clearly this condition (figs. 17, 18, 19). The demarcation of sternal elements and of costal cartilages is shown in the special arrangements of the cartilage cells in lines, along which, later on, the joint cavities will be formed. In all three sterna the sterno-clavicular joint is completely formed, with its inter-articular fibro-cartilage. But in only one case is there a definite costo-sternal joint cavity (between the mesosternum and the right second costal cartilage) (fig. 18)}

(d) Thefurther changes in the cartilaginous sternum preceding ossification occur in rodents (rat, mouse) Without cleavage of the parts of the sternum or separation of costal cartilages. Opposite to the costal attachments the cartilage is distinctly hyaline, poorer in cells, and stained less deeply than in the intervals between the costal cartilages. In these intervals the cells are massed together, stain deeply, and the process of ossification is foreshadowed by the ‘formation of “ primary areolze,” which occur in the centre of the pre-sternum, in the meta-sternum, and in the first four so-called segments of the meso-sternum (figs. 20, 21, 22).


1 Figures 19 (A-J) show the existence of a sternal foramen. In several sections it presented the appearance of fissura sterni. The perforation contained vessels, one of which was of considerable size.


These areolae increase in size, while at the same time the perichondrium becomes enormously thickened, followed by the formation of periosteal temporary bone in the usual way (fig. 22).


Thus at birth (in the mouse, fig. 23), while there is complete fusion of the sternal elements together, and of the costal cartilages with them, there is a distinct differentiation of elements entering into the constitution of the sternum. Bone formation has begun, and cartilage only exists at the extremities" of the pre-sternum and meta-sternum, in the meso-sternum opposite the costal attachments, and in the interval between the attachments of the sixth and seventh costal cartilages (fig. 24).

II. Ossification

The following facts have been derived from an examination of 236 sterna of human embryos between the foetal ages of three to nine months. 2

(A) Dates of oss7;ficat7'on.—The approximate periods of ossification in the component parts of the sternum are shown in Table I., which essentially corroborates the accepted account of the

TABLE I.-—0ss*§fieatz'o-n, of the Ster-num (percentages).

l CENTRE PRESENT. CENTRE ABSENT. I _ m 1 N Z l “J 2".“ as ‘6 0 , § Meso-sternum. g 2 E Meso-sternum. 2 ,3 Z :3 :5 E In E I-1 2 '25 2 5 . 2 ' -if - 2 $9 4 I ‘ Q 33 g <" E 1st 1 2nd 7 3rd 4th .3 5 1st 2nd 3rd 4th «E

2 :5: 2 . mm. 1 1 IX. 122 64'4 96-7 99-2 99-2 2 83-3 29 , 8-1 3-3 3 -8 -8 16-6 71 91-8. VIII. 21 52-3- 81 81 1 76-2 47'6l 9-5i 14-3 l 19 19 23'8 52-3 90-5 85-7 I l VII. 16 49-1 93-3 87-5 3 87-5 62-5 37-5 12-5 6-6% 12-5 12-5 37-5 62-5| 87-5 VI. 3! 40'7 80'6 83'8 77'4 1 54'8 6'4 I 0 l9'3 16'1 22‘5 45'1 93'5 100 V. 7'4 36‘5 62'5 66'6 * 4I‘6 l2°5 4'1 l 0 37'5 33'3 58’3 87'5 958 100 IV. 1 29'6 15'3 23 15'3 7'7 H 77 1 0 84'6 77 8-1'6 92'3 92'3 100 III. ; 23'9 2'2 2'2 2‘2 , 1'1 1 0 0 77'7 77'7 77'7 88'8 100 100 a 4 ,


dates at which the several centres appear. The first nuclei appear generally in the sixth month for the pre-sternum and the first piece of the meso-sternum. In the seventh month centres appear for the second and third pieces of the mesosternum. N 0 further addition to the number of centres occurs during the eighth and ninth months ; and in full-time foetuses (of which 122 examples were examined) the fourth piece of the meso-sternum and the meta-sternum are usually cartilaginous. (B) Position and number of centres of osmfication.-—In Table II. a summary is given of the situation and number of centres of ossification in the component parts of the sternum. A more intimate analysis did not appear necessary; and for the sake of brevity and clearness, reference has been omitted to the separation or fusion of double centres, and to obliquity in their position (such oblique double nodules being grouped as lateral). The results tabulated, it should be noted, are reached from an examination of specimens of which the large majority are fulltime foetuses. The cases of younger sterna are not only fewer in number, but are also less advanced in ossification.


While there is considerable variability both in number and position, the centres of ossification are, as a general rule, single and median, and are six in number; one for the pre-sternum, one each for the first four elements of the meso-sternum, and one for the meta-sternum. Exceptions to this rule are found in all situations except in the meta-sternum, which in the few cases in which bone formation has begun, is invariably provided with a single median centre.

The pre—sternum is generally formed by a single centre (79 per cent.). When there are two centres, they are generally vertica.1ly placed. Three or more centres occur quite rarely (26 per cent.).

The first centre for the meso-sternum is, as a rule, also single (785 per cent.); when there are two, they are usually laterally placed. The second and third centres of the meso-sternum are less frequently single than the above-named centres (593 per cent.: 60'5 per cent.). When there are two centres, they are in most cases laterally placed. The fourth centre in the mesosternum is not generally present. When it occurs it is nearly as often double ‘as single; and when two centres are present, they are as often vertical as lateral in position.


TABLE II.-—-Median and Lateral Ossvgficcttion.

MONtrHs,. . . . .* IX. VIII. I VII. i VI. ’ v. Iv. III. '.ro1uu.. H Pmnonnuens.

5 1 —-L -r ‘ocunj -1:-T .-:——j-—::

14 }9 1 24 3}12 3 4 1 3

1 0} 3 '0 4 0} } 0 }

I27 0 3 }5 .0 1 0 3 17 25 ' 15


I i I

Centre Single, . . _ . . 84 » Double X::~':::::," : 23 }2s ,, Three or more, . . 4

1.

G‘?!

147 179

3g}3: }39 l 209

<1 —¢14—

186 .. ..

78'5

5 147 2 6 .. 30 }35 16.0} 186 _

5}4o 2.6 21 3

137 ,.. ..

7 108 ] 3_8.. 59-3 b.:}74 33 }3::: 40-6

-Lee-nj-——— u--——-—

182 . . . . l 60-5

5 3-5 " 42 } 47 -29-5} 33 . 9}56 6.3 39 3

Pre-sternum.

O rJ"~. 00

7*: CO

1 Total Ossified , . . . . 111 g

Centre Single, . . _ . . Meso-sternum. Double Vertncal, .

so 15 0 12 1 2 12 1 1 FirstPiece. » Lateral, . 25}25}30,1} 2}2 1}1}2 2} 3}3 1} 3}3 4 o 1 o no 17 — 15

,, Three or more, . .

- ‘nj— ._ -_:j-—._

14 26

Total ossined, . . . .

— Centre Single, . V .ti . 5 59 0 12 1] 9 #1 0 5

- er ca .

SecondP1ece. ,, Double Lateral,’ _ 47}52 4} 4}4 I 31 «i}5 4} 5}5 1} (1)}1 _ 14 __

61!-(O r-’% Q1-I

,, Three or more, . . 6} 58 0

1-__.—. T — en;

N963 (N I 1-! 24% b

I O9

17:ta1ossined,. . . . 117 16 24 A 6

Centre Single, . . . 59 7 4 14 1

Third Piece. ,, Double ; 33}33}41 g} 3}3 5}6 ‘ g} 3}3 i (1, 1}_l ,, Three or more, . . 8 1

Q1 55% r"’% CW

.. 5- — :3. -2- an. - ——

Total Ossifled, . . . . 100 10 , 10 ‘ 17 2

Centre Single, .{v .t_ . 7 18 0 1 I 2 3 1 0 th P’ . - "'°‘‘ ° }14 1 } 3 1 } 1 Four 1ece ,, Double ‘Lateral,’ . 7 }u 1 }1 1 }3 1 }1 0 0}1 .1..- .

ONOCN

N 9% 6061930 9% ON

,, Three or more, . . 0

1 -.—_ j us. -7

Total Ossified, . . . . 32 2 i 6 .1

|HOOOfiH|OOOO cl o I l I O

Meta-sternum. Single Centre, .' . . . 10 3 2 V 1 1


The part of the sternum between the attachments of the sixth and seventh costal cartilages is cartilaginous at birth, and the question of its ossification is deferred for the present. It appears that it may be ossified by extension from the fourth piece, though there is reason for believing that in some cases at least it may possess a separate and independent centre.

(0) Fissures: Grooves: Fomm6'na.—One remarkable negative feature characterises the series of foetal sterna examined. In all there is a complete median plate of cartilage, grooved it may be . on one or both sides, perforated in some instances by one or

more holes, but in no single instance is there a fissum storm; A longitudinal groove (Table III.) is characteristic of the foetal

TABLE III.—Grooves.

1' Per Cent. I Months. , lases. Present. Absent.

Present. Absent. ' l IX. 113 75 38 66-3 I 336 1' VIII. 17 6 11 35'2 6467 I VII. 16 13 3 ' 812 18'?

2 VI. 30 24 6 80-0 20-0 V. 24 19 5 79'1 208 IV. A 13 13 0 100 III. 9 8 1 88'8 ll°l Total 222 158 a 64 70'1 29'0 1

meso-sternum, occurring in 158 out of 222 examples, or 7 0'1 per -cent., a proportion which obtains generally for all ages. It may be faint or obvious ; it may be found on one or both aspects of the meso-sternum, and implicate it in the whole or part of its length, but it never appears in the pre-sternum. This grooving of the meso-sternum is probably associated with the method of early development of the cartilage, but it is at the same time plain that it is not necessarily coincident with a bilateral asymcation of the meso-sternum.



TABLE IV.—Stemal Fommina.

. 4-; ——u—

PRESENT.

ABSENT. . . . r more N°- One 1n Two In One 1n TWO 0

M°nth3- » °f - Meta-sternum Meta-sternum Meso-sternum in Lfisfigiand TOTAI“ e . ,

Per

,——-jj ———. 1-: 1-: n-g—- jj:—.jn-g-———_——:_—.._——-———n———

Per

cent No. P“ No. P“ No.

cent. cent.

I Per No. cent. No.

.00

IX. .120 81 67'5 23 VIII. 2o 14 70

VII. 16 10 62-5

VI. 30 20 66'6

I Present :H 1 in meta-sternum 2 in meta-sternum 1 in meso-sternum 2 or more in mesosternum and meta 2 sternum 0

Absent . . . 164 = 69 '4 per cent.

u-100

moo II II II

IV. 13 7 53 '9 5

III. 9 7 77'7

.;:e—-———:u-:a-j-T1-ajjj.-———-——.———-——:——jo

Total present 7;=30‘5 per cent.


V0

I '."

N

v-4 K:

00

‘P

' GO

to H O O O v-I O 00



Sternal foramina (Table IV.) occur only occasionally (in 72 out of 236 cases, or 30'5 per cent.). The number and situation of the perforations are as follows :— 9

Cases. ’ Per cent.

One foramen in the meta-sternum . . . 54 22'8 Two foramina in the meta-sternum . ' . 5 2'1 One foramen in the meso-sternum . . . 8 3'3

Two or more foramina (in the meso-sternum and meta-sternum) . . . . . 5 2'1 7 2 . . . 30'5

The great majority thus occur singly in the meta-sternum, and the pre-sternum is never perforated. From an examination of a human embryonic sternum 9 mm. in length (third month) (fig. 19), one is led to believe that the perforation is due to the persistence of vessels, preventing the conversion of the embryonic connective tissue into cartilage in the middle line.

Like the grooves, these foramina are not improbably causally associated with the mode of early development of the sternum, and it is therefore noteworthy that neither grooves nor foramina occur in the pre-sternum.

(D) Union of sternal elements and costal ea'rtz'lages.—An examination of the mode of union of the parts of the sternum with one another and with the costal cartilages brings out the fact that the connections are much the same in the earlier and later months of foetal life (Table V.).

The pre-sternum and meso-sternum are usually connected together by a fibrous lamina (764 per cent.) opposite the attachments of the second costal cartilages. More rarely they are fused together by cartilaginous union (23'6 per cent.). I have only met with one example (in a 9 months foetus) of a case of alteration in position of the junction to the point opposite the attachments of the third costal cartilages.

The meso-sternum and meta-sternum are usually (77°9 per cent.) united by cartilage, and only exceptionally (221 per cent.) by a fibrous lamina.

The costal cartilages in the centre of the series are generally 30 PROFESSOR PATERSON.

fused with the lateral borders of the sternum, and are not united to it by a. fibrous lamina. The first costal cartilage is also, as a rule (813 per cent.) continuous with the pre-sternum. Occasionally on one side or both the union is fibrous.

The condition of the seventh and eighth costal cartilages has been particularly noted. It is not uncommon for the pair of seventh cartilages to articulate together in front of the sternum (34 cases—14°4 per cent.). (In still fewer cases the same occurs


TABLE V.——7S'epamt'i0n of Ste’/mal Elements and Costal


0a~rtt'lage3. _ - ‘ 3 Months . . . . . . IX. VIII. VII. VI. v. IV. III. 01;; . "" ’ -"'" ' '__’ T 1- '—""' -"—' '"-" ""_" Prggiggnfifm {Fibrous . . . I 75-1 73-9 99-9 37 583 69-2 66-6 =76-4 F Mesojsggrnumj Cartilaginous . . 24-7 21 O . 12-9 41-6 36-7 33-3 =23'6 Meggggrggm Fibrous . . . 31 31-5 31-2 46 9 6 11-1 =22-1 1 Memgfigmum Cartilaginous . . J 63-9 63-4 63-7 66 96-9 166 33-3 =77-9 V Fibrous . . . I 14 25 6'6 0 0 153 111 Fggftflgzgal Cartilaginous . . 76 63-7 80 100 73-2 76-9 33-3 =31-3 Dissimilar . . . 9'9 187 133 0 21°6 7'6 0 Sgvepflh {Separate from sternum 6'6 5'8 18 '7 15-3 0 9 0 :92 OS Cartilage United . . . 93-4 94-2 31-3 34-7 100 91 166 = 3 Eighth costal Separate from sternum 90 100 100 967 100 909 88°8 =95'2 ‘ Cartilage United . . . 99 0 6 3-5 6 9 11-1 = 4-3

1- 4-} r if r I I with the sixth costal cartilage.) In 8 per cent. of the cases the seventh cartilage fails to reach the sternum on one side or both. On the other hand, the eighth cartilage on one side or both is connected with the sternum in still fewer cases (48 per cent.). In rare cases, the 5th, 6th, or 7th cartilage reaches on one side to the middle line of the sternum, its distal end pushing its way forwards through the body of the sternum.

(E) Shape of the meta-ste7°num.—Out of 189 cases, the metasternum is present in 182 (963 per cent.); absent in seven instances (37 per cent.). I have been as careful as possible to discard all examples in which there was the slightest indication that the meta-sternum had been accidentally lost in maceration.

While the shape is extremely variable, it is more often single and median than bifurcated. An undivided meta-sternum occurs in 107 cases (57 '6 per cent.); a bifid meta-sternum in 77 cases (423 per cent.).

(F) Anomalz'es—-epi-sternal cart2Ilages.—One of the most striking features of the series of embryonic sterna examined is the absence of anomalous conditions, and the regularity and symmetry of development. N 0 case of fissum sterml is recorded. One example occurs of transference of the pre-meso-sternal junction to the level of the third costal cartilages. A few instances are found in which one or more costal cartilages (usually the 5th, 6th, or 7th) force their way through the cartilaginous sternum to the middle line. Absence of the meta-sternum, asymmetry in the attachment of costal cartilages, and fusion of contiguous costal cartilages together, also occurred in a few examples.

Epi-sterna! ca7~t'ilages.—-I11 two cases supra-sternal cartilages have been found, situated at the cephalic border of the presternum, between the clavicular articular surfaces. In one case the cartilages are separated from the pre-sternum and fused together; in the other case, they are separate from one another, but continuous with the cartilaginous pre-sternum.

It is not my desire to make any general deductions, or attempt to draw any definite conclusions from these observations at present. The subject is a large one, and is only very partially dealt with in this communication. I have ventured to make this bare statement of fact to the Anatomical Society, partly in order to clear the way for further work on the same subject, and partly to draw attention to some of the general morphological problems associated with a study of the human and mammalian sternum.


Description Of Plates

Fig. 1. Human embryo (sagittal section).

Fig. 2. Rat 9 mm. Section across bottom of praecervical sinus.

Fig. 3. ,, ,, Sagittal section through chest wall.

Fig. 4. ,, ,, Transverse section through middle of chest wall, showing ossifying ribs and absence of sternum.

gig‘ Rat 10 mm’ 1 Magnified seven times, showing clavicles,

7' ” ” }- pregslizernum, meso-sternum, and costal . ' ' ” 1 ” car 1 ages.

Fig. 8. ,, ,,

9' Rat 10 mm’ acteristic features of pre-sternum and Fig’ 10' ” ” meso-sternum.

Fig. 11. Bat 10 mm. { Higher magnification, to show differentiation Fig. 12. ,, ,, of tissue in sternum and costal cartilages.

{ Magnified twenty-eight times, to show char

Rat 13 mm’  Magnified seven times, to show structure and

Fig’ 15' ” ” , connections of sternal elements. ' ' 3! 3)

{ Magnified twenty—eight times, to show general Fig. 16. Rat .13 mm. structure of sternum and connections of ' costal cartilages.

Fig. 17. Human sternum, 3rd month, 8 mm. long, magnified twentyeight times.

Fig. 18. Human sternum, 3rd month, 10 mm. long, magnified twentyone times.

Fig. 19. A-I. Sections of human sternum, 3rd month, 9 mm. long, possessing sternal foramen and 8 costal carti1ages,—-magnified 18 times. J. Reconstruction of same.

Fig. 20. Rat embryo. Coronal section of cartilaginous sternum, showing primary areolae,—magnified seven times.

Fig. 21. Coronal section of older rat’s sternum, showing primary areolae and absence of ossification in last piece of mcso-sternum,-— magnified seven times. I

Fig. 22. Coronal section of older rat’s sternum, showing primary areolae, thickened perichondrium, and absence of bone formation between 6th and 7th costal cartilages. ,

Fig. 23. Coronal section of sternum of mouse a few days after birth, showing bone formation and cartilages.

Fig. 24. Sternum (lower end) of rat 9 days old, showing ossification. ./our/2. o/‘Anal. cal’/zy.s‘. Oct . /900.:

15' a’ ma W/7502:,/1'//2. Cam br/'a’_qe ../ou/5/1.0/'/Irzart. &Pfiy.s*. Uct. 7900.