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#REDIRECT [[Paper - Development of the thoracic vertebrae in man (1905)]]
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| [[file:Mark_Hill.jpg|90px|left]] This historic 1905 paper by [[:Category:Charles Bardeen|CharlesBardeen]] and Lewis described the development of the thoracic vertebrae using human embryos from the [[Carnegie Collection]].
[[Embryology History - Charles Bardeen|Charles Bardeen]]
[[Carnegie Embryos]]:
'''Modern Notes:'''[[Musculoskeletal System - Limb Development|Limb Development]]
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=Development of the Thoracic Vertebrae in Man=
[[File:Charles Russell Bardeen.jpg|thumb|alt=Charles Bardeen|link=Embryology History - Charles Bardeen|Charles Russell Bardeen (1871 – 1935)]]
[[Embryology History - Charles Bardeen|Charles R. Bardeen]]
Professor of Anatomy, the University of Wisconsin, Madison, Wisconsin.
With 7 Plates
There is a somewhat extensive literature dealing with the development
of the spinal column in various vertebrates. The chief stages in its
diiferentiation are fairly well determined. Special attention has been
given to the early development in the lower vertebrates. The recent literature on this subject up to 1897 has been reviewed by Gaupp, 97.‘
Somewhat less attention has been devoted to the mammals. To Froriep, 86, is due a valuable account of the development of the cervical
vertebrae in the cow, and to Weiss, 01, an important description of the
development of the thoracic and cervical vertebra in the white rat.
We shall not attempt to enter here into a description of the early
stages of difierentiation in the spinal axis; that is of the period covering
the formation of the chorda dorsalis and of axial and peripheral mesoblast, the difierentiation of primitive segments, and the origin of the
axial mesenchyme. This period in the human embryo has been well
treated by Kollmann, 91, and some account of it has previously been
given in this JOURNAL (Bardeen and Lewis, 01). We shall therefore
proceed at once to a consideration of vertebral dilferentiation in the axial
Vertebral development in the embryo may be divided into three overlapping periods: a membranous or blastemal, a chondrogenous, and an osseogenous.’
‘Among more recent papers may be mentioned, those of Baldu, 01; Hay,
97; Kapelkin, oo; Manner, 99; Minnich, oz; Ridewood, or; and Schauinsland, o3,
’ In the text books.the flrst or these periods is usually called the precartilage,
prochomlral, or Vorlcnorpel stage, but the condensed tissue from which
the skeletal parts are derived gives rise not only to cartilage but also to
perichondrium and to ligaments. Recognizing this fact, Schomburg, go, has
164 Development of Thoracic Vertebrae in Man
The division of the axial mesenchyme into segments, sclerotomes,
which correspond to the myotomes and spinal ganglia, is marked at an
early stage by intersegmental arteries. Schultze, 96, has shown that
the segmental diiferentiation of the axial mesenchyme extends into the
region dorsal to the spinal cord. Ventrally it does not, however, extend
quite to the chorda dorsalis. Fig. 1, Plate I, illustrates the conditions
existing in the thoracic region of man at this period.
v. Ebner, 88, found in the embryos of several vertebrates a fissure
which divides each sclerotome into an anterior and a posterior portion.
Schultze, in 1896, showed, that in selachians and reptiles this fissure is
represented from the time of its formation by a diverticulum which
communicates with the myocoel. In birds the diverticulum arises secondarily and later becomes fused with the myocoel, and in mammals it
arises after the myocael has disappeared.
In man the fissure becomes distinct in the thoracic region at about the
end of the third week of development (Fig. 2, Plate 1) .' At this period
the median surface of each myotome has become converted into muscle
fibres (Fig. 2, M yo.) . At the same time the mesenchyme in the posterolateral region of each sclerotome has become condensed so that it appears, in a stained section, dark when compared with that of the anterior
half (Fig. 2). At the lateral margin of the anterior halves of the
sclerotomes -the spinal nerves extend out toward the thoracic wall (Fig.
2, Sp. N .). The division between the sclerotomes is still marked by the
intersegmental arteries (Fig. 2). About the chords. dorsalis the cells of
the axial mesenchyme become densely grouped into a perichordal sheath.
The long axes of the cells lie parallel with the chords (Fig. 2, Pch. 8.).
The condensation of tissue which distinguishes the posterior sclerotome
half begins, as mentioned above, in the posterior lateral area of each
called the condensed-tissue stage, the mesenchymal period, and restricted the
term Vorknorpel to the earlier stages of the formation of cartilage. The
term “blastemal” is now-a-days commonly used to designate a mass of
mesenchymal tissue from which organs are to be differentiated, and is applied
to the tissue of the limb-bud before differentiation has commenced. It seems
to me that it would be well to extend this term to the structures flrst dinerentiated in the limb. Thus, “sclerob1astema" would mean the tissue dimerentiated from the blastema. of the leg and destined to give rise to skeletal
structures; myoblastema, the time differentiated for the muscles, and dermablastema that destined for the skin.
‘The figures on this and the following plates are based upon embryos
belonging to the collection of Prof. Mail. I am greatly indebted to him for
the use of these embryos.
Charles R. Bardeen 165
sclerotome. From here the condensation extends dorsally between the
medial surface of the posterior half of the corresponding myotome and
spinal ganglion and gives rise to a dorsal, or neural, process (Figs. 5 and
6, Plate 2, N. P12). At the same time it proceeds ventrally along the distal
margin of the corresponding myotome and gives rise to a ventral or
costal process (Figs. 5 and 6, 0'. Pr.) ; and medially toward the chorda
dorsalis, giving rise to a process which joins about the chorda dorsalis
with a similar one, from the other side of the segment (Figs. 5 and 6,_
Disk). These median processes by their fusion form what has been
termed by Weiss, or, a “horizontal plate.” “Primitive disk ” seems to
me perhaps a better term.
The whole mass of condensed tissue which gives rise to the primitive
dorsal, ventral and median processes has received various designations,
of which that given by Froriep, 83, “primitive vertebral arc ” seems to
be the most Widely accepted. Since, however, it represents much more
than -a vertebral semi-arch, I have previously, 99, suggested for it the
term “ scleromere.” ‘
Figs. 8, 9 and 10, Plate III, represent wax-plate reconstructions of
several scleromeres from the -thoracic region of Embryo II, length '7 mm.
The outlines of the condensed tissue ‘are not so sharp in nature as it is
necessary to make them in a model of this kind. It is believed, however,
that the general form relations are here fairly accurately shown. In
Fig. A, Plate II, of the article by Bardeen and Lewis are shown the relations of the scleromeres to other structures.
During the period of differentiation of the scleromeres the myotomes
undergo a rapid development. The median surface of each myotome
gradually protrudes opposite the fissure of v. Ebner. The dorsal and
ventral processes of each scleromere are then slowly forced into the interval between the belly of the myotome to which it belongs and the one
next posterior, and thus finally they come to occupy an intersegmental
position. It is not, however, correct to call the early processes of the
scleromeres “ myosepta,” as some text-book writers have done. Fig. 4
shows this.
‘By the fissure of v. Ebner each sclerotome is divided into two portions,
of which the posterior in the higher vertebrates plays the chief role in vertebral differentiation. “ scleromere" therefore seems an appropriate designation for the condensed sclerogenous tissue of this half-segment. Goette has
recently, 97, brought forward evidence in favor of the View that primarily in
the digitates there were two vertebrae to each body-segment. In the higher
vertebrates, during embryonic development, the posterior skeletal area of
each body-segment alone develops freely. The anterior area becomes fused
with the scleromere in front.
166 Development of Thoracic Vertebrae in Man
This figure represents a horizontal section passing through several
spinal ganglia, myotomes and neural processes. The last may be seen
extending gradually into the area opposite the myotomic septa, but they
still cover the whole posterior half of the median surface of the myotome
in the region of the section. The processes are connected by membranous
thickenings of the mesenchyme of the anterior half of each segment. These
membranes may be called interdorsal membranes. They correspond to
the interdorsalia of elasmobranchs. Figs. 12, 13, 15 and 16, Idr. M.,
represent these membranes. A line drawn from A to B in Fig. 12 would
pass through an area corresponding to that of the section represented
in Fig. 4.
In the region where the neural and costal processes spring from the
primitive disks membranous septa are likewise differentiated from the
anterior halves of the sclerotomes. These septa serve to unite the successive disks. Each is continuous posterially with -a dense tissue which
strengthens the primitive disk and anteriorly it extends into the neural
and costal processes. The relations of these interdiscal membranes are
shown in Figs. 3, 11, 12 and 13, Ids. m. Since at this period structural
outlines are by no means sharp, the figures based upon wax-plate reconstructions must be taken as semi-diagrammatic. A line drawn from
0 to d in Fig. 12 would represent essentially the plane of the section
shown in Fig. 3. '
During the development of the interdiscal membranes the primitive
disks become hollowed out on the posterior surface. A comparison of
Fig. 2 with Fig. 3 demonstrates this. The perichordal sheath meanwhile
is developed in a ventrodorsal direction so that the area between the
primitive disks becomes divided into right and left halves. Figs. 11, 13
and 7 all show this. Each lateral area is filled with a lightly staining
mesenchynie which is continuous ventrally and dorsally with the tissue
surrounding the spinal column.
Fig. 17, Plate V, represents a sagittal section cut slightly obliquely
through an embryo 12 mm. long. In the region where the chorda
(Oh. d.) is cut, the primitive disks may be seen united by a fairly dense
tissue, the perichordal septum (Sptm.). Posterior to this region the
section passes to one side of the chief axis of the embryo. The intervertebral disks may here be seen separated by a lighter tissue and in the
more posterior portion of the section, which passes still more lateral to
the chordal region, the tissue between the disks is seen to be continuous
with that surrounding the spinal column. In this region the interdiscal
membrane (Ids. m.) is seen anterior, the primitive disk posterior to the
fissure of v. Ebner (F. v. E.).
Charles R. Bardeen 16?
Meanwhile the ventral processes of the thoracic vertebrae extend well
into the thoracic wall, giving rise to primitive ribs, illustrated in Fig. B,
Plate II, in the article of Bardeen and Lewis, 01.
Development proceeds rapidly. In Embryo CIX, length 11 mm., age
about five weeks (Figs. 14-16), the conditions are as follows: The neural
processes are somewhat better developed than those of the preceding stage,
but otherwise are similar in character. The costal processes are considerably farther developed (Bardeen and Lewis, 01, Plate V, Fig. E).
At the angle between the neural and costal processes opposim where they
join the primitive disks a transverse process, but slightly indicated
at the preceding stage, is now fairly clearly marked. Each primitive
disk has become further hollowed out at its posterior surface, owing, in
all probability, to the conversion of its tissue into that of the area
between the disks. The interdiscal membrane (Ids. m.), on the other
hand, has become thicker and has extended anteriorly and posteriorly
about the area between the disks so that this has become completely
enclosed (Figs. 14, 15 and 16). The tissue of each segment immediately anterior to the primitive disk has become greatly thickened and the
line between it and the disk indistinct.
The area between each two primitive disks is still divided by the perichordal septum (Fig. 7). Each half represents the anlage of .a chendrogenous center of the vertebral body. Formation of cartilage has not,
however, begun. The thickening of the ventral margin of the primitive
disk at this stage represents the “hypochordal Spange,” which Froriep
h-as shown to play an important part in the development of the vertebra
of birds and of the atlas in mammals. It -has merely a transitory existence in the thoracic region of man.
Summar_1/.—To sum up briefly, we may say that during the blastemal
period each scleromere becomes divided into two portions, an anterior
and a posterior, characterized by a much greater condensation of tissue
in the posterior. From this condensed tissue arises a primitive vertebra
of Remak, or scleromere, with dorsal (neural) and ventral (costal) processes and a disk uniting them to the mesenchyme condensed about the
chorda dorsalis. From the tissue of the anterior half of each sclerotome
arise membranes which serve to unite the dorsal processes of the scleromeres, interdorsal membranes, and to cover in the areas between the successive disks, interdiscal membranes. The primitive disks become hollowed out posteriorly by a loosening up of their tissue and strengthened
anteriorly by a condensation of the tissue immediately bounding the fissure of v. Ebner. The area between each two disks is bilaterally divided
by a membrane springing from the perichordal sheath. The formation
of a cartilagenous keleton now begins.
168 Development of Thoracic Vertebrae in Man
The tissue relations during this period have been carefully studied in
representatives of most of the chief groups of vertebrates. The form of
the early structures has been less accurately determined because most
investigators have avoided the somewhat laborious methods of plastic
On each side of the blastemal vertebra three primary centers of chondrification appear at about the same time, one for neural process, one for
the costal process and one for the vertebral body. Fig. 7, Plate II, shows
these centers as they appear in a cross section at an early period. Figs.
25, 26 and 27, Plate VI, show the early cartilages of an embryo slightly
older, CXLIV, length 14 mm., age 5% weeks.
The cartilages of the vertebral body develop by a transformation of
the tissue lying between the primitive vertebral disks and surrounded by
the interdiscal membrane. A considerable part of this tissue is derived
from the posterior surface of each primitive disk. At first the cartilage
of the left side is separated from that of the right by the perichordal
septum. Soon this is broken through and the two anlages of cartilage
become united about the chorda. In the thoracic region this union seems
to take place at about the same time dorsally that it does ventrally. A
sagittal section of an embryo at this stage is shown in Fig. 18. The
chorda dorsalis is surrounded by a perichordal sheath. The latter is
encircled by dense intervertebral disks which alternate with light cartilagenous rings. The latter are surrounded by perichondrium which is less
condensed than the tissue of the disks, but more so than that of the
bodies and about the same as that of the perichordal sheath. Ventrally
and dorsally a longitudinal ligament has been differentiated from the
surrounding mesenchyme.
It is probable that the disks seen in this section are formed in part
from the primitive disks, in part from the posterior layer of the anterior
sclerotome halves; in other words, that each is formed about the rudiment
of the fissure of v. Ebner. Compare Figs. 17 and 18. The tissue is concentrically arranged in a way somewhat resembling that of the intervertebral disks of the adult.
The perichordal tissue rapidly decreases in thickness. At the same
time the cartilage of the vertebral bodies grows also at the expense of the
intervertebral disks (Figs. 19, 20, 21 and 22). According to Schultze,
96, the cartilages of the bodies finally fuse to form a continuous cartilagenous column. This does not seem to be the case in man. In all of
the embryos belonging to the collection of Prof. Mall some membranous tissue may be seen separating completely the successive bodies,
Charles R. Bardeen 169
but in embryos between 20 and 40 mm. in length this membrane in the
vicinity of the chords dorsalis is very thin. At the periphery of the
disks the annulus fibrosus is meanwhile differentiated more and more
into a condition resembling the adult (Figs. 17-23, Plate V).
The chorda dorsalis at the period shown in Fig. 18 is of about the
same size at the level of the disks and between them, but as the bodies
increase in size at the expense of the disks the chordal canal becomes enlarged in the intervertebral areas and constricted at the center of the
bodies (Figs. 19, 20 and 21). The chordva loses its continuity and the
chordal cells become clumped in the vicinity of the disks (Figs. 21 and 22)
and finally spread out there in the form of a fiat disk (Fig. 23). At this
last period the perichondrium of. the bodies is again becoming well
marked and the portion of each intervertebral disk in the vicinity of the
chorda dorsalis is better developed than during the stages immediately
preceding. The chordal canal long remains in the vertebral body (Figs.
23 and 24).
The cartilage of the bodies in Embryo CXLIV(Fig. 18) is of an early
embryonic hyaline type. At a slightly later stage (Fig. 19) two regions
may be distinguished, a central and a peripheral. The central cartilage
is denser than that of the preceding stage, while the peripheral cartilage
resembles it. Gradually the cartilage at the center of the body undergoes
further changes. The cells enlarge and become sharply set oflf against the
intercellular substance (Figs. 22, 23 and 24), and finally an invasion of
blood vessels takes place, chiefly from the posterior surface (Fig. 23).
These changes in the cartilage, represented also in Fig. 41, Plate VII,
are preliminary to ossification.
Deposit of calcium salts and actual ossification begins in the distal
thoracic and proximal lumbar vertebrae of embryos about 5 to '7 cm. long
and three months of age. Fig. 42 shows a center of ossification in an
embryo of '70 mm.
During the development of the vertebral bodies changes have been
active in the neural cartilages. At the period represented in Fig. 7, Plate
II, the neural cartilage is «a small, flat body situated in the dorsal process
of the scleromere; from this as a center, pedicular, transverse, anterior
(superior) and posterior (inferior) articular, and laminar processes are
rapidly developed. This structural differentiation is best followed in the
figures representing the models (Figs. 25-36). The pediculazr processes
are at first slender rods (Fig. 26), each of which grows out towards and
finally fuses with its corresponding vertebral body. Froriep has shown
(83) that in the chick this process forms a more essential element of the
body than in mammals. In the atlas it forms a lateral half of the
170 Development of Thoracic Vertebrw in Man
ventral arch, but in the thoracic region of mammals it fuses with the
antero-lateral portion of the corresponding vertebral body. After its
junction with this the pedicle increases in size but otherwise shows no
marked alteration of form.
The transverse process is at first a short projection which lies at some
distance from its corresponding rib (Fig. 26). The cartilagenous rib
rapidly increases in size and at the same time the transverse process grows
outward and forward to meet it (Figs. 29, 32 and 34). At first the
developing cartilage of the rib and that of the transverse process are
embedded in a continuous blastema, but before chondrification has proceeded far, branches from successive intervertebral arteries become anastomosed in the area between the neck of the rib and the transverse
process and separation is efiected (Figs. 36, 38 B and 39).
Between the extremity of the transverse process and the rib a joint is
developed (Figs. 39, 40, 41 and 42), and the surrounding blastema converted into costo-transverse ligaments.
The articul-ar processes develop slowly from the cartilage. Extension
takes place anteriorly, A. A. Pr., and posteriorly, P. A. Pr., in the interdorsal membrane. In an embryo of 14 mm. (Figs. 25, 26 and 27) these
articular plates are separated by a distinct interval. In one of 17 mm.
they have approached each other very closely (Fig. 37) ; and in one of
20 mm. not only do the articular processes show distinctly more form
(Figs. 28, 29 and 30), but in addition the superior articular process
slightly overlaps the inferior (Fig. 38). This overlap of the superior
articular processes is distinctly more advanced in an embryo of 28 mm.
(Fig. 39), and still more so in one of 33 mm. (Figs. 31-33). In an
embryo of 50 mm. (Figs. 34, 35 and 40) conditions essentially like the
adult have been reached.
The laminar processes scarcely exist in Embryo CXLIV (Fig. 26).
In Embryo XXII (Fig. 29) they have begun to project posteriorly to the
region of the articular processes (Fig. 29). The dense embryonic connective tissue covering the laminar processes at this stage gives attachment to a membrane covering, the dorsal musculature, F. D. M ., and to
a membrane surrounding the spinal cord, M. R. D. This accounts for
the two projections seen dorsally on the side of the model representing
the membranous tissue. In Embryo CXLV, length 33 mm., the laminar
processes extend well toward the dorsal line (Figs. 32 and 33) ; in Embryo LXXXIV, length 50 mm. (Figs. 34, 35 and 40), they completely
encircle the spinal canal and from the region of fusion of each pair a
spinous process extends distally, though not so far as in the adult.
Alterations in the cartilage of the neural processes preliminary to
Charles R. Bardeen 171
ossification begin at about the time they take place in the vertebral bodies.
They are first seen in an area which corresponds to that in which the
neural cartilage begins. The earliest calcification appears in Embryo
CLXXXIV, length 50 mm., in the arches of the first cervical to the sixth
thoracic vertebrae.
The development of the ribs I shall not attempt in this place to describe
in detail. Figs. 25-34 and 37-42 show sufliciently well the relations of
the proximal ends of the ribs to the vertebrae. They are developed opposite the intervertebral disks. The blastemal tissue which surrounds the
developing heads of the ribs becomes converted into eosto-vertebral ligaments. Diiferentiation in the cartilage preliminary to ossification takes
place in the shafts of the ribs even earlier than in the vertebral bodies
and in the neural processes. Ossification is well under way in the shafts
of the ribs of Embryo LXXIX, length 33 mm. ; XCVI, length 44 mm.;
XCV, length, 46 mm. ; and LXXXIV, length 50 mm.
Summary of the Ohondrogenous Period of Vertebral Development.Each cartilagenous vertebra is developed from four centers of chondrification. In addition, a separate center appears for each rib. In comparing these centers with the blastemal formative centers, we find that
each primative center of blastemal condensation enters into union with
tissue derived from the anterior half of the body-segment next posterior
and then gives rise to three centers of chondrification, one for the neural
arch, one for the rib and one for half -a vertebra. When ossification first
takes place the centers for the ossification of the neural arches and the
ribs correspond to the original chondrification centers in the blastema,
but the centers for ossification of the bodies show little. trace of the
bilateral condition which marks the cartilagenous fundaments.
The processes of chondrogenous form differentiation are shown in
the drawings of the models. The period of ossification of the vertebrae
has been so often and so well described that no attempt will be made to
enter upon a further acount of it in this paper. I have, however, not
found two primary ossification centers, such as Renault and Rambaud
have described, for each neural arch.
Bum, P.—Die Entwickiung des menschl. Skelets bis zum Geburt. Archiv
mikr. Anat., LV, 245-290, 1900.
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172 Development of Thoracic Vertebree ii. Man
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Physiologie, Anat. Abth., 177-184; 1883, 69-150, 1886.
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849-853, 889-901, 1897.
GoE'rr1=:.—Ueber den Wirbelbau bei den Reptilien und einigen andern Wirbelthieren. Zeitschrift. f. wiss. Zoologie, LXII, 343, 1897.
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MOSER, E.—Ueber das Wachsthum der menschlichen Wirbelsaiile. Dissertation, Strassburg, 1889.
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RIDEWOOD.--O11 the Development of the Vertebral Column in Pipa and
Xenopus. Anat. Anzeiger, XIII, 1901.
SCHAUINSLAND.—UebeI‘SiCht fiber die Entwicklung der Wirbelsfiule in der
Reihe der Vertebraten. Verhandl. Deutsch. Zool. Gesellsch., Wiirzburg, 112-113, 1903.
SCHOMBURG, H.—Entwicklung des Muskeln und Knochen des menschlichen
Fusses. Dissertation, Gfittingen, 1900.
SonUL'rzE.—-Ueber embryonale und bleibende Segmentirung. Verhandl. der
Anat. Gesellschaft, 10 Vers., Berlin, 87-92, 1896.
Wmss, A.—Dle Entwicklung der Wirbelsaiile der weissen Ratte, beonders
der vordersten I-Ialswirbel. Zeitschr. f. wise. Zoologie, LXVI, 492,
WELCKER.-Ueber Bau und Entwicklung der Wirbelsaiile. Zoolog. Anzeiger,
Charles R. Bardeen 173
A. A. Pr., anterior articular process. N. P1'., neural process.
0'. V., cardinal vein. Pch. 8., perichordal sheath.
0'. Pr., costal process. P. A. Pr., posterior articular process.
0021., C(B10lI.l. Pd., pedicle.
Ch. (1., chora dorsalis. Rib, rib.
Den, dermis. Sc1., sclerotome.
Dz‘sIc., intervertebral disk. Sptm., perichordal septum.
D. L., dorsal ligament. Sp. 0., spinal cord.
D. M ., dorsal musculature. Sp. G., spinal ganglion.
F. 17. E., fissure of v. Ebner. Sp. N., spinal nerve.
F. D. M., fascia of dorsal musculature..S'p. Pr., spinous process.
Ids. M., interdiscal membrane. T'rap., trapezius.
Idr. M ., interdorsal membrane. Tr. P12, transverse process.
Is. A., intersegmental artery. V. L., ventral ligament.
L., lamina. V. B., vertebral body.
Myo., myotome. 5, 6‘, 7, 5th, 6th and 7th thoracic vertebrae.
M. R. D., membrane. reuniens dorsalis.
FIGS. 1, 2, 3 and 4. Frontal sections through the thoracic region of several
embryos during the blastemal period of vertebral development. 47.5 diam.
(1) Embryo CLXXXVI, length 3.5 mm. (2) Embryo LXXX, length 5 mm.
(3) and (4) Embryo CCXLI, length 6 mm. (3) Through the region of the
chorda dorsalis, (4) through a. more dorsal plane. Figures 1, 3 and 4 represent sections cut somewhat obliquely so that the right side of the sections
is ventral to the left. In Figs. 2 and 4 on the right side the bodies of several
embryonic vertebrae are represented in outline. In Figs. 2 and 3 owing to
artefacts the myotomes are pulled away from the sclerotomes.
FIGS. 5, 6 and 7. Cross-sections through midthoracic segments during the
blastemal period of vertebral development. 55 diam. (5) Embryo LXXVI,
length 4.5 mm. The right side of the section passes through the middle, the
left side through the posterior third of the 5th segment. (6) Embryo II,
length 7 mm. 5th thoracic segment. The right side of the drawing represents a. section anterior to that shown at the left. (7) Embryo CLXXV,
length 13 mm. The left half of the 6th vertebral body, neural process and rib
are drawn in detail, the body-wall, spinal cord and spinal ganglion are shown
in outline.
FIGS. 8, 9, 10, 11, 12 and 13. Views of models representing the blastemal
stage of vertebral development. (8-10) Embryo II, length 7 mm., 33% diam.
(11-13) Embryo CLXIII, length 9 mm., 25 diam. (14-16) Embryo CIX, length
11 mm., 25 diam. 8, 11 and 14 views from in front; 9, 12, 15, views from the
side; 10, 13, 16, views from behind
174 Development of Thoracic Vertebrae in Man
Frcs. 17-24. Sagittal sections in the mid-line through the 6th, 7th and 8th
thoracic segments of a series of embryos from 12 to 50 mm. long. (17) Embryo CCXXI, length 12 mm. This section includes several segments anterior
and posterior to the three above mentioned, 6th, 7th and 8th. (18) Embryo
CXLIV, length 14 mm. (19) Embryo CVIII, length 22 mm. (20) Embryo
LXXXVI, length 30 mm. (21) Embryo CXLV, length 33 mm. (22) Embryo
LXXIX, length 33 mm. (23) Embryo XCVI, length 44 mm. (24) Embryo
CLXXXIV, length 50 mm.
Fxos. 25-35. Dorsal, lateral and ventral views of models made by the Born
method to illustrate vertebral form-differentiation in the 6th, 7th and 8th thoracic vertebrae during the chondrogenous period. On the left side the cartilagenous, on the right the enveloping fibrous tissue is shown. The latter is
also shown on the eighth vertebra in Figures 29 and 35. (25-27) Embryo
CXLIV, length 14 mm., 20 diam. (28-30) Embryo XXII, length 20 mm.,
13 diam. (31-33) Embryo CXLV, length 33 mm., 10 diam. (34, 35) Embryo
LXXXIV, length 50 mm., 10 diam. (34) Dorsal view, left half; (35) median
Fros. 36-42. Transverse sections through mid-thoracic vertebrae of a series
of embryos. 5 diam. (36) Embryo CVI, length 17 mm. (37) Embryo
CCXVI, length 17 mm. (38) Embryo XXII, length 20 mm. (39) Embryo
XLV, length 20 mm. (40) Embryo LXXXIV, length 50 mm. (41) Embryo
XLIV, length 70 mm. (42) Embryo XXIII, length 70 mm.
The models from which the illustrations in this article were drawn
have been reproduced by Dr. B. E’. Dahlgren at the American Museum
of Natural History, New Y orh, N. Y ., and arrangements may be made
for securing copies by applying to the Director of the Museum.
ch.d. spy.._
Fig.l8 Fis-20.
[[Category:Historic Embryology]][[Category:1900's]]

Latest revision as of 22:13, 21 October 2020