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The growth pattern of the cranial vault in the albino rat as measured by vital staining with alizarine red s Э.

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T H E GROWTH PATTERN O F THE CRANIAL VAULT
TN THE ALBINO RAT AS 3lEASURED BY VITAL
STAINING W I T H SLIZABINE RED “ S ”
MAURP MASSLER’ A N D ISAAC SCHOUR
University of Illinois, College of Dentrstiy, 806 South Wood S t r w t 5
Chicngo 12, Illinois
FOUR FIGURES
INTRODUC’I’ION
The purpose of this investigation was to study the growth
patkern of the cranial vault in the albino rat. An attempt
was made t o designate: ( a ) the sites of growth, (h) the mode
of bony growth at these sites, (c) the chronology and ( d ) the
rates of growth at the different sites.
This program was made possible by the fact that alizarine
red “8,” when injected as a vital dye, selectively stains
actively growing bone (and dentin) (Sehour, ’36).
RETIEW OF TJTTEK~’I’IJRE
The gron-th of the cranial vault has been often deduced
by comparison of youiig arid adult crania (Hatai, ’07 ; Krogman, ’30). I t s growth has bccn investigated only infrequently
by direct espcrimental methods (Troitzky, ’33).
Brasli (’34) used the indirect method of vital staining by
ineaiis of madder feeding in the pig. He explained the growth
of the cranial vault b7 a simple mechanism of esteriial
(ectocraiiial) deposition and internal (endocranial) resorp‘Submitted in partial fulfillment of t h e requirements f o r t h e Degree of Master
of Science in the G m l u a t e Schnol of the University of Illinois.
83
84
MAURY &!IASSLEK. AND ISAAC SCHOUR
tion. H e ascribed to the sutures only the secondary role
of adjustment.
METHODS AND MATERIALS
Vital injections of alizarine red “S” stain the bone,
dentin and cementum growing and calcifying at the time of
the injection. It is, therefore, a vital stain for all the calcifying
tissues except enamel (Schour, ’36). The direct method of
alizarination consists of giving multiple injcctiolis of the
Pig. 1 Cranium of albino r a t virtually injected with alizarine red ‘ S ’ a t one
day of age and sacrificed at 20 days of age. Dark areas, red-staincct bone
growing at the time of thc injection. Light areas, bone formed between one
and 20 days of age.
dye at selected interval’s. After sacrifice, tlie gross specimens
or ground histologic scct,ions sliow the injection effects as
separate lines which can easily he measured. The indirect
method can he used oiily in the young, rapidly growing
animal. It consists of giving a single injection which stains
all the bone present a t that time. This is so since all the
bones a r c actively growing. A sufficient interval is then
GEOTC‘TH
O F CRANIAL VAULT O F RAT
85
allowed to elapse before the animal is sacrificcd. The new
bone formed after the injection appears white (fig. 1).
The indirect method of alizarination was used in this study.
One hundred and thirteen albino rats were each given a
single intraperitoneal injection of a 2% solution of alizarine
red “ S ” a t various ages betwecn birth and 310 days and were
sacrificed three to 90 days later (table 1). The dosage ranged
from 75 to 100mg per kilogram of body weight. The animals were a well-standardized, modified Wistar strain bred
by the Department of Physiology of the University of Illinois.
The analyses were made i q o n the gross macerated wet
specimens. The bones growing a t the time of thc injection
were stained red by the alizarine. The new bone growing
after this time was uncolored (white) (fig. 1). In this manner
the sites of growth a s well as the chronology and rate of
growth at these sites were made apparent. hIeasuremerits of
the amount of new white bone were made from the red edge
of one bone to the red edge of the next at right angles t o the
growing surfaces. The measurements were made under a
dissecting microscope with a caliper and were read against
a stage slide divided into 10ths of a millimeter (table 1).
OBRERVA TT O N 8
Periods of g r n e r a l i w d awl localiwd growth
Vital injections of alizarine red ‘‘8” in rats under GO days
of age resulted in a red stni&ag of all t h e honcs present a t
t h a t time. Microscopic analysis (unstained ground sections)
showed that this generalized staining in the young animal
was due to the fact that bone growth was progressing upon
all’ bony surfaces -periosteal, endosteal, iiitersutural aiid
endochondrab Injecfious of thr dye i~ aninicds over 70 days
of age resulted in t h e red stuuking of only crrtaiw localizrcl
areas, indicating that after the 70th day of age, bony growth
was confined to localized sites.
86
X A U B Y MASSLER A S D ISAAC S C H O L X
TABLE 1
A m o u n t of postnatal bone growth ( i n mm) at various growth sites a t different ages
NO
AXIN.4LS
AGIO A-r
lBJECTlON
AGE A T
INPTIRVA~
SACRIFICE
INTERhAS4L
YETOPIC
SUTURE
SUTURE
SUPERIOR
MARGIN O F
FORAMEN
INTEROCCIPITAL
I n dugs
1.
11.
111.
1V.
v.
0
3
3
0.5
*
*
*
0
10
10
0.5
1.7-3.5
0.6
1.8
2
12
10
0.1
1.5-3.0
0.6
2.0
0.5-1.0
*
1.2
8
6
4
5
13
10
15
20
25
10
10
10
10
10
30
40
70
5
10
20
30
60
10
100
90
20
20
20
40
50
100
20
30
80
16
VI .
7
30
60
30
VJI.
10
41
41
41
71
101
131
30
60
90
VITI.
8
60
90
30
9
70
90
100
100
120
130
30
30
HO
250
310
60
IX.
0.0
0.0
x
0.2
0.7
1.2
1.3
0.0
Growth
ceases
at
3 days
Growth
ceases
Growth
ceases
at
at
10 days
of age
circa
20 days
0.5
0.8
1.2
1.5
1.5
0.0
Growth
ceases
at
circa
20 days
of age
* Growth was so slow- t h a t the amount of new bone formation could not bc nieasurcd grossly. New bone
formation was, however, diseernible.
87
GROWTH O F CRANIAL VAULT O F 1tAT
TABLE 1 - contiiiued
Amount of postnatal bone gromth (in mm) a t zarious growth sites at diffeTent ages
S9QITTAL
SUTURE
I'OSTBRIOR
LdMBDOIUAL
b UTURE
$
&::!"
ANTERIOR
LAMUUOIUAL
ANTERIOR
MARGIN O F
SUTURE
N A S A L BOXF
FRONTONASAL
SVTCRE
CIRCT'MTBXPORAL
SUTURE
TEMpoRAL
CREST
*
*
*
*
*
*
x
..
2.5
2.6
1.5
2.6
1.7
5.0
*
..
2.5
2.7
1.8
2.8
1.3
4.8
2.0
..
1.8
1.5
1.0
1.5
0.8
3.5
1.0
..
0.3
0.7
1.0
1.2
1.6
1.8
0.4
0.6
0.8
1.5
1.7
0.7
1.0
0.9
1.3
1.8
0.6
0.9
1.2
1.8
9.0
1.5
2.5
4.6
6.5
9.0
0.3
0.8
0.8
.*
0.6
0.6
0.8
1.3
1.2
2.3
1.7
2.0
2.4
10.0
*
0.7
0.8
1.2
*
*
2.7
..
x
1.2
1.0
1.3
1.8
*
*
7.0
x
..
0.0
0.0
0.6
1.1
9.3
x
0.6
1.0
1.2
1.3
1.6
2.0
0.2
*
0.5
0.9
1.1
*
*
*
x
Growth
ceases
at
circa
io days
of age
*
*
*
*
*
*
*
*
x
*
x
0.0
0.7
0.8
0.0
Growth
ceases
at
20 days
of age
Growth
ceases
at
30 days
of age
Growth
seams
at
Growth
ceases
a.t
25-30
3040
days
of age
days
of age
*
5.0
*
w
*
x
x
*
*
*
..
..
..
..
I.
..
*
*
*
*
*
* Growth was so slow that the amount of new bone formation could not be measured grossly. New bone
formation was, however, discernible.
88
MAUItY IWASSLER A N D ISAAC SCHOUB
Sites of growth
Increase in cranial size
Iiztersutural growth. This study revealed the sutures to
be the most prolific sites of postnatal growth in the cranium.
Intersutural bone growth was very rapid and quite evident
from birth to 30 days of age. The rate of growth decreased
markedly with age (age gradient), so that after the 30th
day of life growth was confined to only certain of the sutures.
Increase in skull width. Increase in the width of the slrull
was accomplished by growth at the sagittaI complex of
sutures. The sagittal complex consists of three segments :
(a) the internasal suture between the two nasal bones of the
snout, the major site of increase in nasal width; (b) the
metopic or interfrontal suture between the two frontal bones
which contributed t o the increase in bifrontal width; and
(c) the sagittal suture proper between the parietal hones.
The sagittal suture was the site mainly responsible for
the increase in the maximal width of the cranial vault (figs.
1 and 2).
A part of the increase in snout width was contributed by
the lateral growth of the frontal process of the maxillae.
This dimension is not considered in this report and the growth
of the binasal width a t the internasal suture alone was studied.
Increase i n skzill Zewgth. Cranial vault. Increase in the
length of the cranial vault was accomplished primarily by
intersutural growth at the coronal and the anterior and posterior lamhdoidal sutures. The anterior lambdoidal suture
is the lambdoidal suture proper, while the posterior lambdoidal suture is an accessory suture formed bv the presence
of the interparietal bone between the parietals and the occipital bones (figs.1 and 2).
Snout. The frontonaeal suture and the anterior margin
of the nasal bones contribute to the increase in snout length.
The frontonasal suture was the most prolific site of inter-
89
GROWTH O F CRANIAL VAULT OF RBT
sutural growth in the ent,ire skull', a condition to be expected
of a long-snouted animal (tables 1 aiid 3 and fig. 2).
Imzcrease in oault hei.ght. Increase in cranial height was
accomplished by growth a t ( a ) the superior margin of
foramen magnum (which, unlike man, opens posteriorly) ;
SITES
OF GROWTH
AMOUNT FORMED
Post. Lambdoidal
suture
_------------
Ant. Lambdoidal
suture
- - - ~
il
Sagittal suture
Ir
---/-+
-?!---At
birth
Coronal suture-l---Metopic suture
Fig. 2 Diagram indicating the sites and amount of growth in the cranial
vault of the albino rat.
(b) the interoccipital suture lying between the supra and
superior portions of the occipital bone; aiid ( c ) the circumtemporal suture. The interoccipital suture in man begins
to close a t three months in utero aiid is present oiily a s a
cleft or fissure at birth. I n the albino rat, this suture was
a site of active bone deposition until about 20 days of age.
90
MAUFLY MASSLER AND ISAAC S C H O C R
I n the animal under 30 days of age, the anterior and
posterior lambdoidal sutures joined laterallr and met with
the interoccipital and circumtemporal sutures a t the posterior
lateral or mastoid frontanelle above the tympanic bulla. The
interoccipital suture was therefore continuous anteriorly with
the circumtemporal suture and posteriorly with the superior
margin of foramen magnum. These three areas, the free
margin of the occipital bone forming the superior margin
of foramen magnum, the interoccipital suture and the circumtemporal suture thus formed a continuous site of growth at
the side and back of the cranial vault. This complex ran
paralclel to the dorsal aspect of the cranial vault and growth
at these sites contributed the major portion of the increase
in vault height.
Increase in thickness of rault bones
Growth om ectocranial and endocranial s t i r f o w s . Increase
in the thickness of the vault bones was accomplished by the
deposition of hone upon the wto- and endocranial surfaces.
The red staining was readily seen upon both the ecto- and
endocranial surfaces in all animals ZPSS thaiz 70 days of agqc.
The red staining was especially vivid upon the endocranial
surface. Sections cut through the vault and examined under
low power showed a virid staining of the endocranial snrface
of the inner table and of the diploe. There was only mild staining on the ectocranial surface of the outer table. These findings
do not agree with those of Brash ('34) w110 found, in the
pig, new bone growth on the ectocranial surface with resorptions of the endocranial surface.
After the 70th day of age, the red staininq was confined
to only certain areas on the ectocranial surfaces: the area
over the frontal sinuses ; the frontonasal suture ; the temoral crest and circumtemporal. suture complex ; the nuchal
area of muscular attachments and the zygomatic arch. These
sites of growth persisted up to (and probably beyond) 300
days of age.
G R O W T H O F CRAR-IAL VAULT O F IlAT
Rates
a i d chroieology
91
of growth
The absolute rates of growth a t the various sites of growth
studied a re tabulated in table 1. I n all cases the rate of
growth was most rapid a t birth and decreased markedly
with age (age gradient).
The relati~t:rates of growth at the different sntures are
perhaps of greater interest than a re the absolute rates since
these a r e responsible f o r the changes in proportions that
characterize development.
Sagittal complex; (&wrease in cmnial t d t h ) . F rom table 1
it can be seen that the sagittal complex of sntures grew very
slowly and only for a short period of time. Growth at the
internasal. and the interfrontal ( o r metopic) portions was
completed b p the 3rd and 10th days of age, respectively
(tables 1 and 2). The sagittal suture proper grew a little
more rapidly and f o r a longer time, growth beinq completed
at this site by the 20th dav of age (tables 1 and 2).
Since the sagittal compkx of sutures contributed to skull
width, it can be sccn that nasal width was completed by the
third day and miii;mal bifrontal width was virtually completed hp the 10th d a r , while the maximal cranial width (or
bitemporal-crest distance) was attained by the 20th day.
Coronal a i d larnhcloidal sutures (increase i n c r a n i a l k n g t h ) .
The sutures which contributed to the increase in cranial length
grew more rapidly and for a longer period of time than did
the sutures which contributed to the growth in width. The
coronal and lambdoidal sutures not only grew a t a more
rapid rate than did the sagittal sutures, but growth at these
sites persisted f o r a longer time -until the 40th day of age.
Maximal vault width was virtually completed by the 20th
day of life while the increase in vault length ~ - a snot completed until the 40th day. I n addition, growth in length was
accomplished a t tliree sites (coronal, anterior and posterior
l~ambdoidalsutiires), while growth in width occurred a t only
a sincle site (sagittal sutures). These thrcc factors (greater
rate of growth, longer duration, larger number of growth
92
M A U R Y MASSLER A N D ISAAC S C H O U R
sites) readily explained how the round head of the new-born
rat became the elongated tennis racket-shaped head of the
adult rat (fig. 3 ) .
Frolztoiaasnl suture and anterior m a r g i ~of t k e WLSXZE bories
( i m w a s e i j z nasa.Z length). Growth a t the anterior and posterior (frontonasal) margins of the nasal bones was very
rapid and resulted in a marked and rapid increase in the
TABLE 2
Sites and chronology of poslnatal growth of bone in the cranial vault
and snout of the albino rat
AGE A T WHICH
GROWTH CEASES
1. lnerease in width
IT.
-
Sagittal coniplex of sutures
1. Internasal suture
2. Metopic (interfrontal) suture
3. Sagittal suture
lnerease in length (A)
3 days
10 days
20 days
Cranial vault
1. Coronal suture
2. Anterior lambdoidal
suture
3. Posterior lambdoidal
suture
(B)
Circa
30 days
30-40 days
25-30 days
Snout
1. Anterior margin of
nasal bone
2. Frontonasal suture
Circa 70 days
Active after
300 days
111. Increase in height -
1. Superior margin of
foramen magnum
2. Interorcipital suture
3. Cireumtemporal suture
Circa 20 days
Circa 20 days
Active after
300 days
IT. Increase in thickness of vault bones 1. Eetocranial surfare
(generalized)
2. Endocranial surface
(generalized)
60-70 days
Active after
300 days
93
GROWTH O F CRAXIAL VAGLT OF RAT
length of the nasal bones. Growth at the sutural margin
was much more rapid and continued f o r a longer period of
time than a t the free anterior margin. This bone lends
itself to an interesting and provocative study of the rate
and mode of bone growth a t a free and sutural margin.
1 DAY
LO DAYS
30 DAYS
6 0 DAYS
100 DAYS
W
2 0 0 DAYS
Fig. 3 Drawings illustrating the growth o f the eraiiial vault in the albino
rat from one to 200 days.
The frontonasal suture was the site of most rapid growth
in this study (table 1). Its growth continued until the 300th
day of life (possibly longer), while the free anterior margin
of the nasal bones ceased its growth by about the 70th day.
The rapid increase in the length of the nasal bones gave to
94
MAURY MASSLER A N D ISAAC SCHOUR
this animal its typical long-snouted appearance, a characteristic which progressed with age. The increase in nasal length
occurred more rapidly and earlier in the male than in the
female (Hatai, '07).
The snout was quite small in the newborn, while the cranium was relatively large. This relationship is typical of
most mammals, including man, I n the rat, however, the snout
grew at a relatively more rapid rate than did the cranium.
R.lzdo- and ectocranial bogte deposition. It was not possible
to measure the rate of endo- and ectocranial surface deposition of bone in the rat because of the thinness of the bones
and the difficulty in preparing adequate ground sections.
This phase of the problem will be analyzed by vital staining
of the crania of rhesus monkeys.
Growth potential. It is interesting and perhaps significant
to notice the close correlation betwen the rate of growth at
a given site and its chronology. Growth tcnds t o persist for
a longer period of time at those sites where the initial rate
of growth was more rapid. It would appear that different
sites enjoy different growth potentialities and that a greater
amount of growth energy at a given site is expressed at a
faster rate and over a longer period of time.
Sex differences
Differences in the rates of growth at the various sites in
the male and female could be distinguished by the 30th day
of life but did not become prominent until after puberty
(60 days). Tlie female grew at a slower rate than did the
niale, and the various sites of growth terminated at a slightly
earlier age. The female skull was therefore similar to a
male skull- of an earlier chronologic age level. While the
absolute difference between the male and female at a given
site was quite small, the cum4lative effect could be readily
seen in the smalsler size and relatively immature proportions
of the female cranium after 100 days (fig. 4).
Whether the slower rate of growth in the female cranium
was the result of a steeper gradient of growth, a smaller
GROWTH O F CRANIAL VA4ULT O F RAT
95
growth potential, o r both, could not be determined by our
methods. This question (whether sex differeiices in growth
stem from ldifferences in growth potential or growth gradients) is fuiidamental to the underst,anding of tlic phcnoiiicnon
of growth.
130 DAYS
FEMALE
MALE
Fig 4 Drawinga illustrating differences in the cranial vaults of female and
male albino rtas a t 130 days of age.
DISCUSSION
The growth of the cranial' vault is intimately connected
with the growth of the brain and follows the same type of
neural growth curve.
Some texts assume that the cranial cavity enlarges by
external surface deposition and internal resorptions. A
simple mechanism of apposition arid resorption such as
suggested by Brash ( ' 3 4 ) can hardly account for the great
velocity of cranial growth during infancy. Similarly, aberrations in cranial development such as occur in hydrocephalus
and in premature synostoses cannot be understood or explained by such a simple mechanism. This study emphasizes
the primary role of the sutures in cranial development.
96
MAU€LY MASSLRR A N D ISAAC SCHOUR
Vital staining of bone with alizarine red “ S ” shows that
there are, in general, two periods of skeletal growth:
1. A period of generalized bony growth from birth to about
60 days of age, which was characterized by the active deposition of bone upon all bony surfaces. The rate of growth a t
different sites did vary, however (table 1). This period is
characterized by a very rapid increase in the size of the
cranial vault with only minor changes in proportions. The
latter are duc to differences in the rate of growth a t tlie
different sites.
2. A period of localiwd growth after ‘70 days of age characterized by the fact that bonc deposition occurs only a t
certain sites. These sites were, in general, the same that
showed the most rapid rate of growth during the previous
period. Since growth is confined to localized areas, the predominant characteristic of this period is a marked change iii
the proportions of the cranial vault with only a relatively
slight increase in size (fig. 3).
The rat skull is relatively round at birth (fig. 3). As growth
continues, the increase in vault length is more rapid and
extends over a longer period of time than does the increase
in vault width. By the 30th day of life, therefore, the head
becomes markedly elongated. As growth continues from the
30th to the 60th day of life, further elongation occurs (fig. 3).
After the 60th day of life when the period of generalized
ectocranial growth is completed, growth is confined to only
a few localized areas. The most prominent site of red staining
after 60 days is over the frontal sinuses. These areas correspond to the supraorbital ridges of the anthropoids and
apparently serve the same purpose -to permit enlargement
of the frontal sinuses by resorption from within. I n addition,
the areas of muscular attachments continue to grow during
the period of localized growth. The temporal crest becomes
prominent after 60 days of age and continues to grow throughout the normal life-span of the animal. This growth is more
prominent and rapid in the male than in the female.
G R O W T H O F CKhNIAL VAULT O F BAT
97
The growth of the snout at the frontonasal suture contributes markedly to the changes i n proportions that characterize maturity. From a round-headed, small-snouted animal
at birth, the r a t becomes a mesoceplialic animal, with a medium-sized snout. By the 60th day the snout hegins to assume
major proportions. It continues to increase in relative size
after the 60th day, whereas the cranium remains static. BP
the 100th day of life, the r a t head assiimes the proportions
and shape of a tennis racket. Growth of the snout in the male
is more vigorous and contiiiues for a longer period than in
the female.
Modes of growth
Bone growtli at the ectocranial and endocranial surfaces
(inner and outer tables) occurred by simple, surface deposition of bone, one layer upon the other. This mode of grow&
produced a compact type of bone composed of circumferential
lamellae. The diploe (spongy bone) were formed by concomitant resorptions from within, as were the frontal sinuses.
The intersutural growth of bone was very interesting
from many aspects. A given sutural line began (before
birth) as the smooth periphery of a bone. As growth continued
at the free margin of the bone, it made contact with the
periphery of the adjacent bone and thereafter these margins
became serrated and interdigitated.
It is well establsished that under the influence of tension,
a given osteogenic layer will deposit a trabecular type of
bone instead of simple circumferential lamella. This modc
of bone growth is well8illustrated in the alveolar process of the
erupting tooth. A gomphosis type of attachment similar to that
present around tlie tooth root exists at the actively growing
suture. The two ends of the hones are joined together hy the
peg arid hole arrangement of the bony trabecnlae and thc
whole held firmly in place by strands of fibrous connective
tissue. The osteogenic layer upon the endo- and ectocranial
surfaces is continued between the sutures. This arrangement
9s
MATTRY ML4SSLElt AND ISA4AC SCHOUR
permits slight mobility at the sutural junction and rapid
deposition of bone at the same time.
The rapidly expanding brain encased within the cranial
vault exerts a definite internal pressure upon the bones of
the vault. This pressure is translated into a tension force
upon the intersutural periosteum. The intersutural ostegenic
layers under the influence of this tension form ft trabecular
type of bone instead of the simple circumferential layers of
bone seen upon the ecto- and endocranial surfaaes. As growth
continues at the free margins uiider such tension, the trabecnlations become more and more apparent and gross (fig. 3 ) .
TABLE 3
Correlation between the height of sirtural serrations and the chronology of growth
at that suture i n the albino rat
AGE 4T W H I C H
GROWTH CEASES
1. Internasal siitnre
2. Metopic suture
3. Sagittal suture
4. Interoccipital suture
5 . Posterior lanibdoidal suture
6. Anterior lambcloidal suture
7. Coronal suture
8. Cireumtemporal suture
9. Frontonasal suture
-
Circa
3
10
20
Circa 20
25-30
3040
30
Actire a t 300
Active a t 300
days
days
days
days
days
claps
days
days
days
HEIGHT O F SIRRATTONS
IN ADULT MALES
AGE 2 2 0 DAYS
0.0 mm
0.0 mm
0.0-0.3 nini
0.0-0.2 m m
0.0-0.6 111111
0.4-0.7 111111
0.8-1.2 min
(overlapped)
1.0-2.0 nun
The serrations which characterize the sutures are therefore
gross manifestations of this mode of tralnecular growth.
This postulate is supported by the work of Troitzky ('32).
When complete or partial ablation of a given suture was
performed so that there could be no intersutural tension,
the free margin of the parietal bone grew as a smooth line.
When the bone again made fibrous contact with its neighboring bones a i d was once more under a tension force, serrations and interdigitations again blecarne manifest.
Examination of the serratioiis at the different sutures
further supports this hypothesis. Sutures which closed early
G R O W T H O F CRANIAL VAULT O F RAT
99
were not serrated, while those a t which grou7th occurred for
a longer period of time were highly serrated (table 3). The
correlation between the age at which growth ceases at a
given suture and the height of the serrations was good
(table 3).
SUMMARY
The growth pattern of the cranial vault was investigated
by means of vital staining with alizariiie red “ S ” in 113
rats from birth to 300 days of age.
1. There a r e two periods of growth in the skeletal system
of the rat. I n the first, there is a rapid deposition of bone
upon all bony surfaces. I n the second period (aft,er 60 days
of age), growth is localized to certain definite sites.
2. The growth of the cranial vault occuix primarily by
a rapid deposition of bone at the approximating margins
of the bones which comprise the various cranial sutures. Tho
mode of growth (by trabeculation) and the rapid rate a r e
apparently a response to the rapidly expanding encased brain.
Sutural serrations are a gross manifestation of the mode
of trabecular growth.
3. The sutures a r e so arranged in relation to one another
as to perinit each group to contribute to the increase in skull
width, skull length and cranial height. The sites concerned
with growth in each dimension a r e tabulated in table 1.
4. Deposition of bone also occurs upon the endo- and ectocranial surfaces to increase the thickness of the vault bone.
Concomitant internal resorptions form the diploe and frontal
sinn ses.
5. The changes in the proportions of tlie cranial vault
and snout are determined by ( a ) the number of growth sites
in a given direction, ( b ) tlie rate of bone deposition at a
given site and ( c ) the length of time over which growth at
that site is actiye. Skull length increases inore rapidly than
~1;ullwidth hecause a11 three factors are greater in the direction of length over width.
100
MA4CC’RYMASSLER AND ISAAC SCHOUR
The sites of growth and their chronology as well as the
rates of growth at each site for the different ages are indicated in table 1.
6. The order in which growth ceases at the various sutures
and the re1,ation to the height of the suture serrations are
indicated in table 3.
Ririasal width is completed by the 3rd day; minimal bifrontal width by the 10th day; maximal cranial width is
attained by the 20th day. Increase in vault length is virtuallv
completed by the 40th day, while snout length continues to
increase to (and possibly beyond) 3 0 days.
7. The female cranial vault grows at a slcightly slower
rate at the various growth sites than does the male, giving
to the female skull the appearance of a less mature male
skull. It is not known whether this is due to a smaller growth
potential or a greater gradient of growth.
REFERENCES
BRASH,J. C. 1934 Some problems on the growth and developmental mechanics
of bone. Edinburgh Medical J., 41: N. S. IV.
GRERNE,E. 1935 Anatomy of the rat. Trans. h i . Phil. Soc., 97, new series.
H B N D E L S Y A N , 31. B., A N D E. F. GORDON 1930 Growth and bone changes in
rats injer,ted with anterior pituitarF extract. J. Pharmacol. and
Exp. Therap., 38: 349-362.
HATAI,S. 1907 Studies on the variation and correlation of skull measurements
in both sexes of mature albino rats. Am. J. Anat., Y : 423-442.
K R W M S N , W. M. 1930 The problem of growth changes in the face and skull
as viewed from a comparative study of anthropoids and man. Dental
Cosmos, 76: 624-630.
SCIIOT~R,
I. 1936 Measurements of bone growth by alizarine injections. Pror.
Soc. Exp. Biol. and Med., 3 4 : 140-141.
SCEOUR,
I., M. M. HOFFMAN
AND B. G. SARNAT
1941 Vital staining of growing
bones and teeth with alizarine red “ S.” J. Den. Res. 20 ( 5 ) : 411-418.
SCIEOUR,
I., AND M. MASSTAIR 1940 Postnatal craniofacial and skeletal dereloprnent in the albino rat and the Mararus rhesus monkey a s demonstrated
by vital in,jections of aliznrine red “8.”
Anat. Rec., 76: no. 2, suppl.
no. 2, Feb. 24, 984.
TODD,T. W., ..“D D. Mr. LYONS 1924 Endocranial suture closure: I. Adult
males of white stock. Am. J. Phys. Anthrop., 7: 325-384.
1925 Ectocranial suture closure: IT. Adult males of white stock.
Ibid., 8: 2 3 4 6 .
G R O W T H O F CBANIAL VAULT O F RAT
TROITZKY,
101
VON WL. 1932 Zur F r a g e der Formbildung ded Sehadeldaches
(Experimentelle Unterscburig der Schadeldathnlhte und der damit
verbundenen Erscheinungen) Zeits. f . iMorphol. and Anthropol., SO :
504-530.
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