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Patten BM. Embryology of the Pig. (1951) The Blakiston Company, Toronto.
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This historic 1951 embryology of the pig textbook by Patten was designed as an introduction to the topic. Currently only the text has been made available online, figures will be added at a later date. My thanks to the Internet Archive for making the original scanned book available.
Patten BM. Developmental defects at the foramen ovale. (1938) Am J Pathol. 14(2):135-162. PMID 19970381
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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History | Historic Embryology Papers) |
Embryology of the Pig
Frontispiece
Reconstruction (X 17.5) showing the organ systems of a 9.4 mm. pig embryo. For explanation see figures 60 and 66.
By BRADLEY M. PATTEN
Professor of Anatomy in the University of Michigan Medical School
THIRD EDITION
WITH COLORED FRONTISPIECE
AND 186 ILLUSTRATIONS IN THE TEXT (CONTAINING 412 FIGURES) OF WHICH 6 ARE IN COLOR
Philadelphia : THE BLAKISTON COMPANY : Toronto
Third Edition
Copyright, October 1948, by The Blakiston Company
BY P. Blakiston ’s Son & Co.
Copyright, 1951, by P Blakiston’s Son & Co , Inc.
Preface to Third Edition
In making the revision for a new edition of this book it did not
seem desirable essentially to change its form or scope. Effort has been
concentrated on improving the presentation of the original subject
matter and bringing it up to date, rather than on its expansion. The
entire book has been reset to a greater page width which has permitted enlarging certain of the illustrations that, in earlier editions,
had proved to be too greatly reduced. With the generous cooperation
of the publishers several of the important plates on the cardiovascular
system have been remade to a larger scale and with color. A number
of new illustrations have been drawn for sections where experience
has shown that students needed additional graphic assistance in
interpreting their laboratory material. It is hoped that these changes
will all contribute toward making the book as a whole more serviceable.
Bradley M. Patten
August 1048
Preface to First Edition
This book represents an endeavor to set forth in brief and simple
form the fundamental facts of mammalian development. The thread
of the story and the illustrations have been based on pig embryos
because of their value and availability as laboratory material. But
special stress has been laid on the embryological phenomena involved
instead of on the details of specific conditions existing in the pig.
Throughout the book, every efTort has been made to present developmental processes as dynamic events with emphasis on their sequence
and significance, rather than as a series of still pictures of selected
stages.
Obviously no book can deal fully with all phases of development, even in a single form, and still remain serviceable as a text. As this book is for the student, it has seemed expedient, for the sake of clearness and simplicity, to omit many things which I should like to have included. My primary aim has been to write an account in which the essentials stand out adequately interpreted and unobscured by a multiplicity of details — to lay a foundation which can be further built upon in accordance with special needs or individual desires.
Bradley M. Patten
January 1927
Acknowledgment
The pleasantest thing about working on this book has been the generous aid I have received from many sources. Throughout the preparation of the initial edition the encouragement, criticism, and suggestions of my colleagues, Dr. F. C. Waite and Dr. S. W. Chase, were of the greatest help. In the preparation of material and in making the illustrations for the first edition the beautifully accurate work of Miss Kathryn Toulmin was of inestimable value. In making the new drawings added in the third edition I was fortunate in securing the unusually able assistance of Mrs. Dorothy Van Eck.
Dr. G. L. Streeter and Dr. C. H. Heuser of the Carnegie Institute allowed me free use of their extensive collection of young embryos and generously gave me many photographs made from their material. To Mrs. Charles S, Minot I am indebted for permission to use several figures from the late Professor Minot’s works. The accrediting in the figure legends of these and other borrowed illustrations by no means covers my obligation to other writers. Practically the entire bibliography is a statement of indebtedness for information and ideas.
I wish I might acknowledge individually the helpful services rendered by many of my students, but they are too numerous. Several reconstructions which I have used directly or indirectly have been largely their work. Of even greater assistance have been their suggestions during the shaping of the work — suggestions of especial value because they were made from a point of view difficult for an instructor to appreciate without such aid.
To The Blakiston Company, I am indebted for much helpful cooperation and especially for their liberality with regard to the number and quality of the illustrations.
No person other than my wife could have deciphered and put into usable form manuscript of the character I frequently turned over to her for revision and typing. Without her generous help the preparation of the text would have been much more arduous and long delayed.
Bradley M. Patten
Chapter 12
Tke Histogenesis of Bone and tlie Development of tke Skeletal System
I. Histogenesis of Bone
Histologically bone belongs to the group of tissues known as the connective and supporting tissues. In spite of their widely varying adult conditions these.tissues are all similar in that the secreted parts, rather than the cells themselves, carry out the functional role characteristic of the tissues. It is the secreted, fibrous portion of the binding connective tissues which ties together various other tissues and organs ; it is the secreted matrix of cartilage and of bone which affords rigid support and protection to soft parts and furnishes a lever system on which the muscles may be brought into play.
The cellular elements of these tissues must not be overlooked, however, in emphasizing the functional importance of the cell products. The cells are, so to speak, the power behind, in that they extract the appropriate raw materials from the circulation, elaborate them within their cytoplasm, and deposit the characteristic secretion as an end-product. Moreover after the fiber is formed or the matrix is laid down, it is dependent on the cells for maintenance in a healthy active conditidn.
Embryologically the entire connective-tissue group arises from mesenchymal cells. It is not surprising, in view of their closely related functions and their derivation from a common type of ancestral cell, that one type of connective tissue may be converted into or replaced by another. This facility for changing the type of specialization is sometimes referred to as plasticity.
The plasticity of the connective-tissue series is well exemplified in the development of bone. Bone does not form in vacant spaces. It is always laid down in an area already occupied by some less highly specialized member of the connective-tissue family. The formation of some bones begins in areas already occupied by connective tissue — such bones are said to be intramembranous in origin, or are spoken
271
272 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
of as membrane bones. Other bones are laid down in areas already
occupied by cartilage. In this case they are said to be pndochondral in
origin, or, are called cartilage bones. It should be clearly borne in mind
that these terms apply solely to the method by which a bone develops
and do not imply any differences in histological structure, once the
bone is fully formed.
Likewise we should know at the outset what histologists mean when they speak of cancellous bone and compact bone. These terms refer not to the method of origin of the bone but to its density when fully formed. Developmen tally all bone goes through the spongy or cancellous stage. Some bones later become compact, others remain cancellous. Most bones are compact in some areas and cancellous in others.
The subject of bone development can be presented more simply if we take up first the formation of primary cancellous bone intramembranously ; then the method by which this same type of spongy bone is formed within cartilage, and finally the changes by which cancellous bone, formed in either of the above ways, may become secondarily compact.
Intramembranous Formation of Primary Cancellous Bone. In
an area where intramembranous bone formation is about to begin we find an abundance of mesenchymal cells congregated and numerous small blood vessels present. The mesenchymal cells soon exhibit a tendency to cluster together in more or less elongated groups here and there throughout the area. If we study a group of this type which has been aggregated for a short time we can make out the beginning of a definite plan of organization. Near the axis of the cord delicate fibers appear, produced by the secretory activity of the cells. As this fibrous strand becomes more definite, the cells tend to become ranged against it (Fig. 151, A). In so doing they retract the cytoplasmic processes which are so characteristic of undifferentiated mesenchymal cells and become rounded. In this stage we have essentially a connective tissue in which the fibrous strands are for the most part rather widely separated from one another, and in which each strand has, lined up against it^ the cells responsible for its production.
The actual deposition of bone matrix begins very soon after the establishment of these primordial strands of mesenchymal cells and fibers. In fact one usually finds the formation of bone beginning on the older part of a strand while the strand itself is still being extended at one end by the aggregation of more mesenchymal cells (Fig. 151,
HISTOGENESIS OF BONE
273
I'k;. 151, Formation of trabeculae of membrane bone. Projection drawings from the mandible of a pig embryo 130 mm. in length (cf. Fig. 182).
Abbreviations: Matrix cal., ossein matrix impregnated with calcium salts; Matrix oss., ossein matrix not yet impregnated with calcium salts.
A). When the mesenchymal cells ranged against the fibrous axis of such a strand become active in the secretion of calcareous material they are spoken of as osteoblasts. We should not lose sight of the fact that they are the same cells which formed the fibrous axis of the original strands, given a new name in deference to their further specialization and altered internal chemistry.
In studying the deposition of bone matrix one must bear in mind its dual nature. The matrix consists of an organic fibrous framework which is impregnated by a subsequent deposit of inorganic calcium compounds. We may liken the matrix of bone to reinforced concrete* In the making of a road or a wall, a meshwork of steel is first placed in the forms and concrete is then poured in. The steel gives the finished structure tensile strength and a certain amount of elasticity, the concrete gives form and hardness. So in bone the organic fibers {ossein fibers) impart strength and resilience, while the calcium salts whh which the fibers are impregnated give to the completed matrix body and rigidity.
274 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
The two steps in the deposition of bone matrix may be demonstrated readily in areas where active bone forma^tion is going on,
owing to the fact that the presence of calcium compounds- in a tissue
markedly increases its affinity for stains. Even after most of the calcium salts have been removed from the ossein framework by treatment
of the tissue with acids (decalcification) to permit the making of
sections, the staining reaction is still apparent. This indicates that
the ossein fibers in which calcium has once been deposited are more
or less permanently changed chemically even though all the calcium
possible is subsequently removed.
If we look at a strand on which the osteoblasts have been active for a time (Fig. 151, B) we see, next to the osteoblasts, a zone of bone matrix which takes very little stain. This is the newly deposited organic portion of the matrix as yet unimpregnated with calcium salts. It consists of a feltwork of minute fibers so delicate and so closely matted together that it is very difficult in ordinary preparations to see the individual fibers at all. Slightly farther from the osteoblasts the matrix is densely stained (Fig. 151, B). This part of the matrix has been impregnated with calcium salts, chiefly phosphates and carbonates, and has thereby been converted into true bone matrix. The calcium utilized by the osteoblasts in this process is brought to them by the blood stream where it is carried in soluble form, probably in organic linkage. It is interesting to note in this connection that the presence of calcium and of phosphates in the blood is not in itself all that is necessary for this process. There must be present also sufficient vitamin D, which in some way facilitates the extraction by the osteoblasts of these raw materials from the blood and their deposition in insoluble form as part of the bone matrix. The absence of vitamin D from the system results in the formation of bone matrix deficient in calcium salts and therefore lacking in rigidity — a cohdition not infrequent in pigs. Stock raisers have miscalled this condition rheumatism but it is really the same condition known medically as rickets.
In the deposition of the matrix, the fibrous core of the original strand serves as a sort of axis on which the first matrix is laid down. When such a strand is completely invested by bone matrix, it is called a trabecula (little beam). As the osteoblasts continue to secrete and thereby thicken the trabecula, the accumulation of their own product forces them farther and farther away from the axial strand about which the first of the matrix was formed. The new matrix added is not laid down uniformly. It is possible to make out in it markings
HISTOGENESIS OF BONE
275
which are suggestive of the growth rings of a tree. Apparently the
osteoblasts work more or less in cycles, depositing a succession of thin
layers of matrix. Each of these layers of the matrix is called a lamella
(Fig. 152). As the row of osteoblasts is forced back with the deposit of
each succeeding lamella, not all the cells free themselves from their
secretion. Here and there a cell is left behind. As its former fellows
Erythroblast extruding nucleus
Reticular connective-tissue cell j Erythroblast in mitosis Young erythroblast
Normoblast Blood vessel .
Fat cell --tHemocytoblast —
Granuloblast - Hemocytoblast in mitosis
Polykaryocyte.
Osteoblast ^ t
I
Bone cell
Bone
lamella
Fio. 152. A small area of bone and adjacent marrow
as seen in highly magnified decalcified sections. The
drawing has been schematized somewhat to emphasize
the relations of the cytoplasmic processes of the osteoblasts* and the bone cells so important in nutrition. In
the adjacent marrow developmental stages of various
types ofiiiijioQd cells, have been
continue to pile up new matrix, it becomes completely buried (Fig,
151, B). An osteoblast so caught and buried is called a bone cell
{osteocyte)^ and the space in the matrix which it occupies is called a
lacuna. The bone cells, thus entrapped, of necessity cease to be active
bone formers, but they play a vital part in the maintenance of the
bone already formed. They have delicate cytoplasmic processes
radiating into the surrounding matrix through minute canalidhli.
The processes of one cell come into communication with the processes
of its neighbors (Fig. 152). Thus the bone cells nearer to blood vessels
276 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
Fig. 153. Diagrams showing stages in establishing of a characteristic area
of primary cancellous bone by extension and coalescence of originally
separate trabeculae.
absorb and hand on materials to their more remote fellows which in turn utilize these materials in maintaining a healthy condition in the organic part of the bone matrix. It is the senescence of these cells with the consequent lowering of their efficiency and the resultant deterioration of the ossein component of the matrix which is in part responsible for the decreased resiliency of the bones in advanced age.
As the various trabeculae in an area of developing bone grow, they inevitably come in contact with each other and fuse. Thus trabeculae, at first isolated, soon come to constitute a continuous system (Fig. 153). Because of its resemblance to a latticework (Latin — cancellus), bone in thb condition, where the trabeculae are slender and the spaces between them extensive, is known as cancellous bone. The spaces between the trabeculae are known as marrpw spaces.
Endochondral Bone Formation. As the term implies, endochondral bone formation goes on within cartilage. It cannot be stated too strongly that cartilage does not, in this process, become converted int# bone. Cartilage is destroyed and bone is formed where the cartilage used to be. The actual bone formation is essentially the same as in the case of membrane bone. The phenomena of special
mSTCXJENESIS OF BONE
277
interest in connection with this type of bone development are those
involved in the destruction of the cartilage preliminary to the formation of bone.
Cartilage Formation. To trace the process logically we must start back with the formation of cartilage. The first indication of impending chondrogenesis is the aggregation of an exceedingly dense mass of mesenchymal cells. This cell mass gradually takes on the shape of the cartilage to be formed. The histogenetic changes involved are not at first conspicuous. During the period of preliminary massing the cells have been migrating in from surrounding regions and also increasing the local congestion by rapid proliferation. As they are packed in together they lose their processes and become rounded (Fig. 154, A, 1). When it seems as if no more cells could possibly be crowded in, the course of events changes. The cells begin to separate from one another. This is due to the fact that they have become active in
Fig. 154. Photomicrographs of developing cartilage. The areas photographed were from the margins of the paranasal cartilage of pig embryos between 25 and 30 mm. in length. For location of cartilage in head see figure 175.
A, Early stage showing: at (1) the massing of mesenchymal cells which were about to be incorporated in the growing margin of the cartilage; and at (2) an area where matrix formation is already beginning.
B, Slightly more advanced stage of the same cartilage showing: at (1) increase in the amount and density of the matrix in the center of the growing cartilage; at (2) concentration of the surrounding mesenchyme to form tire perichondrium; and at (3) the addition of new cartilage matrix peripherally*
278 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
secreting. It is the accumulation of the secretion of the cells which
gradually forces them farther and farther apart unti^ they come to lie
isolated from one another in the matrix they have produced (Fig. 1 54,
A, 2). Such a method of increase in m^ss, where there are many
scattered growth centers contributing independently to the increase
in bulk of the whole, is known as interstitial growth. This interstitial
growth of young cartilage stands in sharp contrast to the appositional
growth of such rigid substances as bone or dentine or enamel where
the matrix is laid down in successive layers one upon another. Obviously interstitial growth implies plasticity of the substance produced.
Were the substance produced unyielding, the very activity of a number of growth centers within it would soon crowd those growth centers
to obliteration.
As the cartilage matrix is increased in amount its affinity for basic stains becomes more marked, due probably to increase in concentration of the characteristic substance in it known chemically as chondrin. At the same time the matrix becomes more rigid with a resultant checking of interstitial growth. The cells continue to secrete to a certain extent, however, as evidenced by the fact that in mature cartilage the matrix immediately surrounding the cells becomes more dense than the rest of the matrix. This area of denser matrix around the lacuna in which the cell lies is known as the capsule. As the cartilage grows older the capsules become more conspicuous and many of them come to contain more than one cell. These nests of cells in a common capsule are the result of cell divisions, following which the daughter cells are held imprisoned in the original capsule of the mother cell — further evidence of the loss of plasticity in the matrix.
The formation of a matrix so rigid that interstitial growth is checked, takes place first centrally in an area of developing cartilage. When the center has become too rigid for interstitial growth to continue, appositional growth begins to take place peripherally. While the cartilage has been increasing in mass it has been acquiring a peripheral investment of compacted mesenchyme. This investing layer of mesenchyme soon becomes specialized into a connectivetissue covering called the perichondrium. The layer of the perichondrium next to the cartilage is less fibrous than the outer layer and the cells in it continue to proliferate rapidly and become active in the secretion of cartilage matrix. For this reason it is known as the chondrogenetic layer of the perichondrium. It is through the activity (rf the chondrogenetic layer that the cartilage continues to grow
Cartilage
ceil
Cart. trab. 1
Osteoblast
— Bone
ntotrix
Bone trabecula
Periosteum
Fig. 155. Drawing showing periosteal bud and an area of endochondral
bone formation from the radius of a 125 mm. sheep embryo. The small sketch
indicates the location of the area drawn in detail.
Abbreviations: Cart, eros., area from which cartilage has recently been eroded; Cart, pre-eros., area with cartilage cells enlarged and arranged in rows presaging erosion; Cart, trab,, remnant of cartilage matrix which has become calcified and serves as an axis or core about which bone lamellae are deposited to form a bone trabecula; Mes., mesenchymal cell.
279
280 HISTOGENESIS OF BONE AND DEVEI.OPMENT OF SKELETAL SYSTEM
peripherally, by apposition, long after interstitial growth has ceased
in the matrix first formed. ^
Cartilage Erosion. When a mass of cartilage is about to be replaced by bone, very striking changes in its structure take place. The cells which have hitherto been secreting cartilage matrix begin to destroy the matrix. The lacunae become enlarged and a curious arrangement of the cartilage cells becomes evident. The cells erode the cartilage in such a manner that they become lined up in rows (Fig. 155). This process of destruction continues until the cartilage is extensively honeycombed. Meanwhile the tissue of the perichondrium overlying the area of cartilage erosion becomes exceedingly active. There is rapid cell proliferation and the new cells, carrying blood vessels with them, begin to invade the honeycombed cartilage (Fig. 155).
The Deposition of Bone. It is a striking fact that during its growth cartilage is devoid of blood vessels, the nearest vessels to it being those in the perichondrium. The invasion of cartilage by blood vessels definitely determines its disintegration as cartilage, and at the same time is the initial step in the formation of bone. For this reason the enveloping layer of connective tissue, up to this time called perichondrium because of its relation to the cartilage, is now called periosteum because of the relations it will directly acquire to the bone about to be formed. This change will not be confusing if we stop to think that both these terms are merely ones of relation, which translated mean, respectively, that tissue which surrounds cartilage, and that tissue which surrounds bone. The important fact to bear in mind is that this enveloping layer of tissue is of mesenchymal origin and therefore contains cells of the stock that may develop into any of the connectivetissue family to which bone as well as cartilage belongs. When, therefore, a mass of periosteal tissue {periosteal bud, Fig. 155) grows into an area of honeycombed cartilage it carries in potentially boneforming cells. These cells come to lie along the strand-like remnants of cartilage, just as in membrane bone formation osteoblasts ranged themselves along fibrous strands. The actual deposition of bone proceeds in the same manner endochondrally as it does intramembranously. The only difference is that in one case a strand-like remnant of cartilage serves as an axis for the trabecula, whereas in the other case deposition begins on a fibrous strand. Extensions and fusions of the growing trabeculae soon result in the establishment of typical cancellous bone similar to that formed intramembranously.
HISTOGENESIS OF BONE
281
The Formation of G)mpact Bone from Primary Cancellous
Bone. The difference between cancellous bone and compact bone is
architectural rather than histological. The fundamental composition
of the bone matrix, its lamellation, and the relations of the bone cells to
the matrix, are the same in both cases. It is the way in which the
lamellae are arranged that distinguishes these two types of bone from
each other. In cancellous bone the disposition of lamellae is such that
it leaves large marrow spaces between the trabeculae. In compact
bone there has been a secondary deposit of concentrically arranged
lamellae in the marrow spaces which greatly increases the density of
the bone as a whole.
The essential differences between the two, and the way in which cancellous bone may become converted into compact bone, can be illustrated by a simple schematic diagram. Figure 156, 1, shows the arrangement of lamellae and marrow spaces in primary cancellous bone. The osteoblasts which have formed the trabeculae still lie along them on the surface toward the marrow cavity. If such an area is to IxTome compact, these osteoblasts enter on a period of renewed activity and deposit a series of concentric lamellae in the marrow cavity. Frequently if the marrow spaces are irregular there is a preliminary rounding out of them by local resorption of the bone already formed (Fig. 156, 2). This is then followed by the deposition
Fig. 156. Diagram showing transformation of cancellous to compact bone. The solid lines indicate the lamellae of primary cancellous bone; the dotted lines show the subsequently added concentric (Haversian) lamellae which nearly obliterate the marrow spaces of cancellous bone. The sequence of events is indicated by the numbers. Note that irregularly shaped spaces in the cancellous bone may be rounded out by absorption before the concentric lamellae are laid down.
282 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
of the concentrically arranged lamellae, sometimes called Haversian
lamellae after the man who first described them in detail (Fig. 156, 3 ).
In this process the original marrow spaces are reduced to small canals
{Haversian canals^ into which have been crowded the blood vessels
which formerly lay in the marrow cavities (Fig. 156, 4 ). These canals
maintain intercommunication with each other in the substance of the
bone, constituting a network of pathways over which the bone receives
its vascular supply. As compared with the marrow spaces of cancellous
bone, however, they are very small; and the gross appearance of a
bone which has undergone this secondary deposit of concentric
lamellae amply justifies characterizing it as ‘'compact.’’
II. The Development of the Skeletal System
In dealing with the development of the skeletal system we must recognize at the outset that the subject is far too extensive to be covered here with anything like completeness. It is not difficult, however, to become acquainted with the outstanding features in the development of two or three characteristic bones, as, for example: the sequence of events in the formation of a flat bone; the steps involved in the establishment and growth of a long bone; the way separate ossification centers appear in a common primordial cartilage mass and give rise to the various parts of a vertebra. Familiarity with such type processes gives one an understanding of the factors operative in the development of the skeleton as a whole and a background sufficient to permit ready and intelligent following up of developmental details in specific bones in which one may become interested.
Development of Flat Bones. The flat bones, such as the bones of the cranium and face, are for the most part of intramembranous origin. We are, therefore, already familiar with the early steps in their development from our study of the histogenesis of membrane bone (Figs. 151 and 153). After a mass of primary cancellous bone has been laid down in a configuration which suggests that of the adult bone being formed, there appears about this mass a peripheral concentration of mesenchyme (Fig. 157, A). This periosteal concentration of mesenchymal tissue contains potentially bone-forming cells which soon become active and lay down a dense layer of parallel lamellae about the spongy center of the growing bone (Fig. 157, B). Anatomically this dense peripheral portion is known as the outer table of the bone. The inner portion, which in the flat bones usually remains cancellous, is called the diploii. The original mesenchymal tissue which
THE DEVELOPMENT OF THE SKELETAL SYSTEM
283
Periosteum
Marrow space
l^one trabeculae
A
Subperiosteal bone lamellae
Bone trabeculae
Marrow space
Periosteum
Fig. 157. Diagrams showing the manner in which the dense peripheral
layer of a flat bone is formed by the deposition of subperiosteal lamellae about
an area of primary cancellous bone.
I
remains in the marrow spaces of the diploe develops into characteristic “red bone marrow†rich in blood-forming elements (Fig. 152).
The story of the growth of the mandible, a membrane bone which starts after the manner of flat bones but which later takes on a very elaborate shape and finally becomes largely compact, can be gleaned by a comparative study of figures 178, 180, and 184.
Development of Long Bones. The long bones are characteristically of endochondral origin. The cartilage in which they are performed is a tempiorary miniature of the adult bone. Ordinarily there are several ossification centers involved in the formation of long bones. The first one to appiear is that in the shaft or diaphysis. The location of this center is shown schematically in figure 158, A, Such
B
284 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
b
A
Fig. 158, Diagrams showing liie progress of ossification in a long bone.
The stippled areas represent cartilage; the black areas indicate bone.
A, Primary ossification center in shaft. B, Primary center plus shell of subperiosteal bone. C, Entire shaft ossified. D, Ossification centers have appeared in the epiphyses. E, Entire bone ossified except for the epiphyseal cartilage plates.
details as the cartilage erosion which preceded its appearance and the manner in which the deposit of bone was initiated have already been considered (Fig. 155). Our interest now is in the relation of such an endochondral ossification center to other centers, and to the bone as a whole.
Almost coincidently with the beginning of bone formation within the cartilage the overlying periosteum begins to add bone externally (Fig. 158, B). In view of the fact that the bone-forming tissue carried into the eroded cartilage arose from the periosteum, this activity of the periosteum itself is not surprising. Moreover we have already encountered this same phenomenon of periosteal bone formation in the outer table of flat bones.
The formation of bone which starts at about the middle of the shaft soon extends toward either end until the entire shaft is involved (Fig. 158, C), leaving the two ends {epiphyses) still cartilage. Toward the end of fetal life ossification centers appear in the epiphyses. The number and location of these epiphyseal centers vary in different long bones. There is always at least one center in each epiphysis and there may be two or more. Not uncommonly there are two centers in one epiphysis and one in the other, as illustrated in figure 158, D.
Between the bone fojcmed in the diaphysis and that formed in the epiphysis there persists a mass of cartilage known as the epiphyseal plaie which is of vital importance in the growth in length of the bone.
THE DEVELOPMENT OF THE SKELETAL SYSTEM
285
We should expect from the rigidity of bone matrix that interstitial
growth could not account for its increase in length. This was long ago
demonstrated experimentally by exposing a developing bone and
driving into it three small silver pegs, two in the shaft and one in the
epiphysis. The distance between the pegs being recorded, the incision
was closed and development allowed to proceed until a marked
increase had occurred in the length of the bone. On again exposing
the pegs, the two in the shaft were found to be exactly the same
distance apart as when they were driven in, but the distance between
the pins in the shaft and that in the epiphysis had increased by an
amount corresponding to the increase in length of the bone. This
indicates clearly that the epiphyseal plates constitute a sort of temporary, plastic union between the parts of the growing bone. Continued
increase in the length of the shaft is accomplished by the addition of
new bone at the cartilage plate. These epiphyseal plates persist during
the entire postnatal growth period. Only when the skeleton has
acquired its adult size do they finally become eroded and replaced
by bone which joins the epiphyses permanently to the diaphysis.
As the bone increases in length there is a corresponding increase in its diameter. The manner in which this takes place is also susceptible of experimental demonstration. If madder leaves, or some of the alizarin compounds extracted from them, be fed to a growing animal, the bone formed during the time the feeding is continued is colored red. If the madder is discontinued, bone of normal color is again formed ; but the color still remains in the bone laid down while madder was being added to the diet. Thus it is possible, by keeping a record of alternate f>eriods of feeding and withholding madder and comparing these records with the resulting zones of coloration in a bone, to obtain very accurate information on the progress of bone growth and resorption. Applied to the development of long bones this method shows their increase in diameter to be due to continued appositional growth beneath the periosteum. As the bone is added to peripherally there is a corresponding resorption centrally. This central resorption results in the formation of a cavity in the axis of the long bone which is called the marrow canal (Fig. 158, C). With the further increase in the diameter of a bone, its marrow canal becomes correspondingly enlarged. A significant mechanical fact might be cited in this connection. 'Engineers have determined that the strongest rod which can be made from a given weight of steel is obtained by molding it into tubular form. The development of an essentially tubular shaft by
286 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
progressive increase in the size of the marrow cavity gjivcs a long bone
maximum strength with minimum weight.
The Formation of the Vertebrae. The development of the vertebrae is of interest to the student primarily because it exemplifies so excellently a fundamental embryological phenomenon — the origin of separate parts from an undifferentiated primordial tissue mass, and the subsequent association of these parts to form an organized structure. In studying young embryos we traced the history of the mesodermic somites through their early differentiation. It will be recalled that from the ventro-mesial face of each somite there arises a group of mesenchymal cells called collectively a sclerotome (Fig. 42). These cells migrate from either side toward the mid-line and become aggregated about the notochord. From these masses of cells the entire vertebral column is destined to arise.
The first significant change which takes place in these primordial masses is the clustering of sclerotomal cells derived in part from each of the two adjacent somites into groups which are located opposite the intervals between the myotomes. In studying series of transverse sections this arrangement is easy to overlook unless the density of the cells about the notochord is carefully noted in passing from section to section. It shows very clearly, however, in frontal sections (Fig. 159). Each of these cell clusters is the primordium of the centrum of a vertebra. Once formed they rapidly become more dense and more definitely circumscribed (Fig. 160). Soon after the centrum takes shape, paired mesenchymal concentrations extending dorsally and laterally from the centrum establish the primordia of the neural arches and of the ribs (Fig. 161).
Fig. 159. Semi-schematic coronal sections through the dorsal region of young embryos to show how the vertebrae became intermyotomal in position. Note that the primordium of a centrum is formed by cells originating from the sclerotomes of both the adjacent pairs of somites.
THE DEVELOPMENT OF THE SKELETAL SYSTEM
287
Fig. 160. Transverse section from pig cm])ryo of 17 mm. cut at the level of the lungs to show the structures in the dorsal body-wall. (After Minot.)
mantle layer ependymal
marginal layer
of eord
neural arch
of cord
layer
eympathetic ganghon
anterior cardinal vein
left left duct erihre fetdium vt Ctteter
Fig. 161 . Transverse section of 20 mm. pig embryo cut at the level of the lungs
to show the developing vertebra and ribs. (After Minot.)
288 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
Fig. 162. Transverse section from 40 mm. pig embryo cut at the level of the lungs to show the developing vertebra and ribs.
The Stage in w^hich the various parts of the vertebrae arc sketched
in mesenchymal concentrations, is frequently spoken of as the blastemal stage. It is rapidly followed by th^ cartilage stage. Conversion to
cartilage begins in the blastemal mass first in the region of the centrum
and then chondrification centers appear in each neural and each
costal process (Fig. 161). These spread rapidly until all the centers
fuse and the entire mass is involved (Fig. 162). The cartilage miniature of the vertebra thus formed is at first a single piece showing no
lines of demarcation where the original centers of cartilage formation
became confluent, and no foreshadowing of the separate parts of
which it will be made up after the cartilage has been replaced by
bone. Shortly before ossification begins the rib cartilage becomes
separated from the vertebra, but the vertebra itself remains in one
piece throughout the cartilage stage (Fig. 162).
The locations of the endochondral ossification centers which appear in a vertebral cartilage are indicated schematically in figure 163. It readily can be seen how the spreading of these centers of bone formation will establish the conditions which exist in an adult vertebra. The median ossification center gives rise to the centrum. The centers in the neural processes extend dorsally to complete the neural arch. The spinous process in most of the vertebrae is formed by a prolongation of these same centers to meet dorsal to the neural canal.
Fig. 164. Diagram of four types of vertebrae indicating the parts derived
from the different ossification centers shown in figure 163. The part formed by
the median center in centrum is cdncentrically ringed; the parts arising from
the costal centers are stippled; parts derived from the lateral centers in the
neural arches are indicated in line-shading,
289
290 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
In forms such as the pig the spinous processes of tl>e more anterior
thoracic vertebrae are very long. In these vertebrae additional ossification centers appear in the spinous process and fuse with those in the
Scapula Humerus
Radius Mandible
& ulna
Fig. 165. Photograph (X 1/^ showing the
ossification centers which have appeared in pig
embryos of 35 mm. This and the two following
figures were made by photographing in transmitted light embryos in which all the uncalcified
tissues had been rendered transparent by treatment with potassium hydroxide and glycerine.
neural processes. The transverse processes with which the tubercles of the ribs articulate are formed by the lateral extension of the primary ossification centers in the neural processes. These same centers extend ventrally also, and meet the centrum (cf. Figs. 163 and 164).
Scapula
/ Humerus
Fic. 166. Photograph (X IM) showing the progress of ossification in the skeleton of a 65 mm. pig embryo.
Fig. 167. Photograph {X showing the extent of ossification in the skeleton of a 90 nun. pig embryo.
292 HISTOGENESIS OF BONE AND DEVELOPMENT OF SKELETAL SYSTEM
The shaft of the rib is formed by extension of its primary ossification center (Fig. 163). After birth, secondary epiphyseal centers
appear in the tubercle and head of the rib. These centers are separated from the shaft by persistent cartilage plates in the manner
described in discussing the development of long bones. Fusion of the
secondary epiphyseal centers with the shaft of the rib does not take
place until the skeleton has acquired its adult dimensions.
The foregoing discussion has been based on a thoracic vertebra in which the relations of the rib to the vertebra show most clearly. All the vertebrae have the costal element represented, although it is greatly reduced and modified in other regions than the thoracic. A study of figure 164, in which the components of vertebrae from the cervical, thoracic, lumbar, and sacral regions are schematically indicated, will make the homologies apparent. With these homologies in mind it is sufficiently evident, without going into further detail, how all these vertebrae arise by a process similar to that described for the thoracic vertebrae.
The Progress of Ossification in the Skeleton as a Whole. It
would carry us beyond the scope of this book to take up the development of specific bones. Each has its own story involving the formation of the connective tissue or the cartilage mass which precedes it ; local erosion centers if it be preformed in cartilage; number, location, and time of appearance of ossification centers; growth in length and diameter; development of epiphyses; time of fusion of epiphyses and diaphysis; and finally the development of muscle ridges and articular facets. Without entering into a discussion of details of this sort, it is possible nevertheless to follow the general progress of ossification in the skeletal system as a whole. Embryos which have been treated with potassium hydroxide and then cleared in glycerine clearly show the various ossification centers. In such preparations the areas where calcium salts have been deposited stand out white in reflected light and opaque in transmitted light. ^Figures 165-167, which are photographs of preparations of this type, can be used to trace the history of the more important bones. It should perhaps be stated explicitly that these figures arc included primarily to give a general view of the progress of ossification and secondarily to afford a readily available source of reference for following up points of interest that may arise. It is not a profitable use of the student’s time to attempt to memorize the ossification centers which have appeared in embryos of any given age.
Chapter 13
Tke Development of tke Face and Jaws and tke Teetk
I. The Face and Jaws
The Stomodaeum. In studying the early development of the digestive tract we saw that the primitive gut first appeared as a cavity which was blind at both its anterior and posterior ends (Fig. 37). Its opening in the future oral region is established by the meeting of an ectodermal depression, the stomodaeum, with the cephalically growing anterior end of the gut. The stomodaeal depression, even as late as the time the oral plate ruptures and establishes communication between the anterior end of the gut and the outside world, is very shallow (Fig. 40). The deep oral cavity characteristic of the adult is formed by the forward growth of structures about the margins of the stomodaeum. Some idea of the extent of this forward growth can be gained from the fact that the tonsillar region of the adult is at about the level occupied by the stomodaeal plate when it ruptures. The growth of the structures bordering the stomodaeum, then, not only gives rise to the superficial parts of the face and jaws, but actually builds out the walls of the oral cavity itself.
The Jaws. Because the face of a young embryo is pressed against the thorax it is difficult to study unless the entire head is cut off and mounted separately. Preparations of this kind observed under a dissecting microscope by strong reflected light show the surface configuration of the facial region very clearly. The most conspicuous landmarks are the stomodaeal depression, which in view of its fate we may now call the oral cavity, and the olfactory pits. In embryos as small as 7 mm. most of the structures which take part in the formation of the face and jaws are already clearly distinguishable (Fig. 168). In the mid-line cephalic to the oral cavity is a rounded overhanging prominence known as the Jrontal process. On either side of the frontal process are horseshoe-shaped elevations surrounding the olfactory pits. The
293
294
DEVELOPMENT OF FACE, JAWS AND TEETH
median limbs of these elevations are known as the nap-medial processes
and the lateral limbs are called the naso-lateral processes.
Growing toward the mid-line from the cephalo-lateral angles of the oral cavity are the maxillary processes. In lateral views of the head (Figs. 31 and 32) it will be seen that the maxillary processes and the mandibular arch merge with each other at the angles of the mouth. Thus the structures which border the oral cavity cephalically are: the unpaired frontal process in the mid-line, the paired nasal processes on either side of the frontal, and the paired maxillary
Fig. 168. Face of 7 mm. pig embryo photographed X 15. Note especially the unmistakably paired character of the thickenings which later fuse in the mid-line to complete the mandibular arch.
processes at the extreme lateral angles. From these primitive tissue
masses the upper jaw and the nose are derived.
The caudal boundary of the oral cavity is less complex, being constituted by the mandibular arch alone. In very young embryos (Fig. 168) the origin of the mandibular arch from paired primordia is still clearly evident. Appearing first on either side of the mid-line are marked local thickenings due to the rapid proliferation of mesenchymal tissue. Until these thickenings have extended from either side to meet in the mid-line there remains a conspicuous mesial notch. With their fusion, the arch of the lower jaw is completed (Figs. 1 69172).
THE FACE AND JAWS
295
In 10-12 mm. embryos (Fig. 169) very marked progress can be
seen in the development of the facial region. The maxillary processes
are much more prominent and have grown toward the mid-line,
crowding the nasal processes closer to each other. The nasal processes
have grown so extensively that the frontal process between them is
completely overshadowed (cf. Figs. 168 and 169). The growth of the
Fig. 169. Face of 11 ,5 mm. pig embryo photographed X 12. Fusion of the right and left components of the mandibular arch is practically complete. Both the medial and lateral limbs of the horseshoe-shaped nasal processes have undergone conspicuous enlargement. Note especially the approximation of each naso-medial process to the maxillary process of the same side.
medial limbs of the nasal processes has been especially marked and
they appear almost in contact with the maxillary processes on either
side.
The groundwork for the formation of the upper jaw is now well laid down. Its arch is completed by the fusion of the two nasomedial processes with each other in the mid-line, and with the maxillary processes laterally (Fig. 170), The premaxillary bones carrying the incisor teeth are formed, later, in the part of the upper jaw which is of naso-medial origin. The maxillary bones, carrying all
296
DEVELOPMENT OF FACE, JAWS AND TEETH
the upper teeth posterior to the incisors, are developed in the part of
the arch arising from the maxillary processes.
Nasal Chambers. The olfactory pits have by this time become much deepened, not only by the growth of the nasal processes about them, but also by extension of the original pits themselves which soon break through into the oral cavity (Figs. 93 and 97, C). We may now
lateral
process
naso*‘ medial process
tojngue
hyomandibular
cleft
hyoid arch
Fig. 170. Face of 16 mm. pig embryo photographed X 10. The
naso-medial processes have fused with the maxillary processes on
either side, and with each other in the mid-line, thus completing
the arch of the upper jaw.
speak of the external openings of the nasal pits as the nostrils {external nares) and their new openings into the oral cavity as posterior nares or nasal choanae. The septum of the nose is formed by fusion in the midline of the original naso-medial processes'; the upper part of the bridge of the nose is derived from the frontal process; and the alae of the nose arise from the naso-lateral processes (Fig. 172).
Naao-Iacrimal Duct. Where the naso-lateral process and the maxillary process meet each other there is formed iot a time a well
THE FACE AND JAWS
297
Fir;. 171. Face of 17.5 mm. pig embryo photographed X 10. The originally separate processes have now largely lost their identity in the series of fusions which have taken place in the formation of the face.
marked groove, which extends to the mesial angle of the eye (Fig. 169).
This is known as the naso4acrimal groove. It soon closes over superficially (Fig. 171), and it is usually stated that the deep portion of the
original groove is converted into a tube, the naso-lacrimal duct^ or
tear duct, wjhich drains the fluid from the conjunctival sac of the eye
into the nose. Recently Politzer has maintained that the nasolacrimal duct arises as an independent epithelial downgrowth from
the conjunctival sac which follows closely along the line of closure of
the old naso-optic furrow.
Tongue. While these changes are going on externally, the tongue is being formed in the floor of the mouth. Anatomically the tongue is usually described as consisting of a freely movable part called its body, and a less freely movable portion, called its root, by which it is attached in the oro-pharyngeal floor. The body of the tongue arises from a small median elevation, the tuberculum impar^ and paired lateral lingual primordia. These elevations appear very early in development on the inner face of the first branchial (mandibular) arch (Fig. 173, B). The tuberculum impar grows slowly and is soon crowded in on
298
DEVELOPMENT OF FACE, JAWS AND TEETH
by the more rapidly growing lateral lingual primordia which form
the great bulk of the body of the tongue (Fig. 173, c5.
Fig. 172. Face of 21.5 rum. pig embryo photographed X 10. The characteristic features of the adult face are even at this early stage clearly recognizable. The regions of the upper jaw and nose which have arisen from originally distinct primordia are differentiated by shading. Vertical hatching indicates origin from frontal process; stippling, from naso-lateral processes; small crosses, from naso-medial processes; horizontal hatching, from maxillary processes. The entire lower jaw is derived from the mandibular arch.
Arising in the pharyngeal floor at the bases of the second and
third branchial arches is an elevation known as the copula (i.e., yoke)
THE FACE AND JAWS
299
because of the way it joins these arches together (Fig. 173, B). The
copula, supplemented by some tissue from the adjacent basal portions of branchial arches 2, 3, and 4, gives rise to the root of the
tongue.
All the various elevations which thus take part in the formation
- Branchial arch i
-Branchial arch 2
'Branchial arch 3 .Branchial arch 4 -Glottis
Lateral lingual anlagt
Copula
Epiglottis
Glottis
Branchial arch i
Lateral lingual anlage
Branchial arch $
Branchial arch 4
Arytenoid ridge
c
Fio. 173. Dissections of pig embryos made to expose the floor of the mouth and show the development of the tongue. (After Prentiss.) A, 7 mm.; B, 9 mm.; C, 13 mm. (All figures X 12.)
B
Tuherculum impof
Branchial arch 2
Epiglottis
Glottis
Lateral lingual anlage
Tuherculum impar
Epiglottis Arytenoid ridge
Branchial arch i
Tuherculum impar
Branchial arch 2
Branchial arch 3 Branchial arch 4
Arytenoid ridge
300
DEVELOPMENT OF FACE, JAWS AND TEETH
THE FACE AND JAWS
301
of the tongue must be thought of as composed of an outer covering
and the underlying mesodermal tissue which causes the covering to
bulge into the lumen. The covering tissue arises in situ from the lining
of the branchial arches involved. The sensory innervation of the surface of the tongue is, therefore, just what one would expect from the
basic relations of the cranial nerves to the branchial arches. The
epithelium of the body of the tongue gets its sensory supply from the
lingual branch of the mandibular division of the trigeminal (V) nerve
(Fig. 97, A, B), and from the chorda tympani branch of the seventh
nerve. The root of the longue receives its sensory fibers from the glossopharyngeal (Fig. 94) and vagus nerves.
The skeletal muscle that makes up the main mass of the tongue beneath the mucosal covering is derived from mesodermal cell masses that are believed to migrate into the pharyngeal floor from the myotomes of the occipital somites. Ontogenetically, in mammalian embryos this migration is exceedingly difficult to trace, for the cells of myotomal origin early mingle indistinguishably with the local mesenchymal cells. Nevertheless the way the hypoglossal nerve (XII), which is the cranial nerve arising at the level of these occipital myotonies, grows in with the developing lingual muscles (Figs. 93, 94, and 97, A, B) and innervates them, furnishes strong circumstantial evidence for this interpretation of tongue muscle origin and migration.
Palate. Coincidently also the palatal shelf is being formed in the upper jaw and separating off the more cephalic portion of the original stomodaeal chamber. Since it is into this cephalic portion of the cavity that the nasal pits break through (Figs. 93 and 97, C), the formation of the palatal shelf in effect prolongs the nasal chambers backwards so they open eventually into the region where the oral cavity becomes continuous with the pharynx.
The palate as well as the arch of the upper jaw is contributed to by both the naso-medial processes and the maxillary processes. From the premaxillary region a small triangular median portion of the palate is formed (Fig. 174). The main portion of the palate is derived from the maxillary processes. From them shelf-like outgrowths arise
Fig. 1 74. Photographs (X 6) of dissections of pig embryos made to expose the roof of the mouth and show the development of the palate. A, 20.5 mm.; B, 25 mm.; C, 26.5 mm.; D, 29.5 mm.
The diagrams of transverse sections are set in to show the relations before (E) and after (F) the retraction of the tongue from between the palatine processes.
302
DEVELOPMENT OF FACE, JAWS AND TEETH
on either side and extend toward the mid-line (Fig. 174, A— G). When
these palatal shelves first start to develop, the tongue lies between
them (Fig. 174, E). As development progresses the tongue drops down
(Fig. 174, F); the palatal shelves are extended toward the mid -line
and finally fuse with each other medially and with the premaxillary
process anteriorly to complete the palate (Fig. 174, D). At the same
time the nasal septum grows toward the palate and becomes fused
to its cephalic face (Figs. 174, F, and 178). Thus the separation of
Fig. 175. Transverse section of snout of 28 mm. pig
embryo (X 12). The area included in the rectangle is
shown in detail in the following figure.
right and left nasal chambers from each other is accomplished at the
same time that the nasal region as a whole is separated from the oral.
II. The Development of the Teeth
The Dental Ledge. Local changes leading toward tooth formation can be made out in the jaws of embryos as small as 1 5 mm. or even less. By the time a size of 28-30 mm. has been attained, a definite thickening of the oral epithelium can readily be seen on both the upper and the lower jaw. This band of epithelial cells which pushes into the underlying mesenchyme around the entire arc of each jaw is known as the labi<Hlental ledge {labio-dental lamina) (Figs. 175 and 176). Shortly after its first appearance, cross-sections show this ledge
THE DEVELOPMENT OF THE TEETH
303
of epithelial cells to be differentiating into two parts, a more distal
part which by its ingrowth marks off the elevation which is to become
Fig. 176. Drawing (X 130) showing labio-dental ledge of 28 mm. pig embryo. For location of area represented see preceding figure.
Fig. 177. Drawing (X 130) showing differentiation of the labio-dental ledge into labio-gingival lamina and dental ledge.
The ingrowth of the labio-gingival lamina initiates the separation of the lip from the gum (gingiva). From the dental ledge a series of local bud-like outgrowths are formed, each of which gives rise to the enamel cap of a tooth.
The region shown is the same as that in the preceding figure but from a slightly older (37 mm.) embryo.
the lip from that which is to become the gum, and a more proximal part which is destined to grow into the gum and give rise to the enamel-forming organs of the teeth. The part of the original labio
304
DEVELOPMENT OF FACE, JAWS AND TEETH
dental ledge which separates the lip from the gum (gingiva) is known
as the labio-gingival lamina^ and the part of the original ledge which is
to take part in tooth formation is known as the denial ledge or dental
lamina (Fig. 177).
Enamel Organs. Soon after the dental ledge is established, local buds arise from it at each point where a tooth is destined to be formed. Since these cell masses give rise to the enamel crown of the tooth they are termed enamel organs. As would be expected, the enamel organs
nasal bone
cartilage of
nasal septum
nasal
chamber
nasal process
of premaxilla
dental papilla enamel organ
labiogingival
lamina
Meckel’s cartilage
tooth germ
mandible
Fig. 178. Drawing (X 10)tDf a transverse .section of the snout
of a 71 mm. pig embryo. The area included in the rectangle is
shown in detail in the following figure.
for the milk teeth are budded off from the dental ledge first, but the
cell clusters which later give rise to the enamel of the permanent teeth
are formed at a surprisingly early time (Fig. 180). They remain
dormant, however, during the growth period of the milk teeth and
begin to develop actively only after the jaws have enlarged sufficiently
to accommodate the permanent dentition.
The histogenetic processes involved in the formation of milk teeth and permanent teeth are essentially the same. It is, therefore, sufficient to trace them in the case of the milk teeth only, keeping in mind that the same process is repeated later in life in the formation of the permanent teeth.
In a section of the developing mandible which cuts the dental ledge
THE DEVELOPMENT OF THE TEETH
305
at a point where an enamel organ is being formed, the shape of the
enamel organ suggests that of an irregularly shaped, inverted goblet,
the section of the dental ledge appearing somewhat like a distorted
stem (Fig. 178). The epithelial cells lining the inside of the goblet early
take on a columnar shape. Because they constitute the layer which
secretes the enamel cap of the tooth, they are called ameloblasts (enamel
formers) (Fig. 179). The outer layer of the enamel organ is made up of closely packed cells which are at first polyhedral in shape but which soon, with the rapid growth of the enamel organ, become flattened. They constitute the so-called outer epithelium of the enamel organ (Fig. 179). Between the outer epithelium and the ameloblast layer is a loosely aggregated mass of ceils called collectively, because of their characteristic appearance, the enamel pulp or the stellate reticulum (Fig. 179).
306
DEVELOPMENT OF FACE, JAWS AND TEETH
Fig. 180. Developing tooth from lower jaw of a 120 mm. pig embryo (X 14). The small sketch including half of the tongue (left) and part of the lip (right) gives the relations of the region drawn. The area in the rectangle is shown in detail in the following figure.
Fig, 181. Projection drawing (X 350) of segment of enamel organ and adjacent pulp from a 120 mm. pig embryo to show ameloblast and odontoblast layers. For location of area represented see preceding figure.
THE DEVELOPMENT OF THE TEETH
307
The Dental Papilla. Inside the goblet-shaped enamel organ
there is caught a mass of mesenchymal cells which are said to constitute the dental papilla (Fig. 179). The cells of the dental papilla
proliferate rapidly and soon form a very dense aggregation. The outer
cells of this mass are destined to secrete the dentine of the tooth and
the inner cells to give rise to the pulp of the tooth.
A little later in development the enamel organ begins to assume the shape characteristic of the crown of the tooth it is to lay down (Fig. 180). At the same time the outer cells of the dental papilla take on a columnar form similar to that of the ameloblasts (Fig. 181). They are now called odontoblasts (dentine formers) because they are about to become active in secreting the dentine of the tooth.
In the central portion of the dental papilla vessels and nerves arc beginning to make their appearance so that the picture is already suggestive of the condition seen in the pulp of an adult tooth. Meanwhile the growth of the dental papilla toward the gum has crowded the stellate reticulum of the enamel organ in the crown region so it is nearly obliterated (Fig. 180). This brings the ameloblasts of this region much closer to the many small blood vessels which lie in the surrounding mesenchyme. The approach of the ameloblasts to the neighboring vascular supply would appear to be significant, since it is precisely here at the tip of the crown where the ameloblasts first begin to secrete enamel (Fig. 182).
By the time the enamel organ has been well established the dental ledge has lost its connection with the oral epithelium, although traces of it can still be identified in the mesenchyme at the lingual side of the tooth germ (Fig. 180). The cluster of cells which is destined to give rise to the enamel organ of the permanent tooth of this level can be seen budding off from the ledge close to the point from which the enamel organ of ffie milk tooth arose (Figi >^).
Formation of Dentine. With these preparatory developments complete, the tooth-forming structures are, so to speak, ready to go about the fabrication of dentine and enamel. As is the case with bone, enamel and dentine are both composed of an organic basis in which inorganic compounds are deposited. We may use the same comparison that was used in describing bone : that of the familiar use in construction operations of a steel meshwork into which concrete is poured, the steel giving the finished structure some degree of elasticity and increasing the tensile strength while the concrete gives body and solidity. In the case of such hard structures in the body as bone, dentine, and
308
DEVELOPMENT OF FACE, JAWS AND lEETH
pr^ordiutn enamel organ
' permanent tooth
odontoblast layer
pulp of tooth
enamel pulp (stellate reticulum) periosteum of alveolar socket outer epithelium of enamel organ
Fig. 182. Developing tooth from lower jaw of a 130 mm. pig embryo
(X 30). The small sketch gives the relations of the regions drawn. The area
in the rectangle is shown in detail in the following figure.
blood vessel dentine enamel blood vessel in
1 i, 1 mesenchyme
fiber lirocess of enamel organ
Fio, 183. Projection drawing (X 350) of small segment of developing
THE DEVELOPMENT OF THE TEETH
309
enamel, these interlacing organic strands in the matrix give the tissue
its resilience and tensile strength, and the calcareous compounds
deposited in the organic framework give form and hardness.
Although bone, dentine, and enamel are similar in having both organic and inorganic constituents in their matrix they are quite different in detail, both as to composition and microscopical structure. Bone has approximately 45 per cent of organic material while dentine has but 30 per cent and adult enamel 5 per cent or less. There is also considerable difference in the kind and proportion of inorganic compounds present in each. Structurally they are totally unlike. Bone matrix is formed in lamellae and has cells scattered through it. Dentine is formed without lam^llation and has its cellular elements lying against one face and sending long processes into tubules in the matrix. Enamel is prismatic in structure and the cells which form it lie against its outer surface while it is being deposited, but are destroyed in the eruption of the tooth.
The first dentine is deposited against the inner face of the enamel organ, the odontoblasts drawing their raw materials from the small vessels in the pulp and secreting their finished product toward the enamel organ. It is significant in this connection that in an active odontoblast the nucleus, which is the metabolic center of the cell, has gravitated toward the source of supplies and come to lie in the extreme pulpal end of the cell (Fig, 183). Also, the end of the odontoblast toward the enamel organ, where the elaborated product of the cell is being accumulated preparatory to its extrusion, can be seen to take the stain especially intensely. Although our knowledge of intracellular chemistry is as yet exceedingly fragmentary and we do not know the exact chemical nature of the product in this stage, the staining reaction is clearly indicative of the presence of calcium compounds of some sort.
If attention is turned now to the recently formed dentine, two zones distinctly different in staining reaction can be seen. The zone nearer the cells is pale, taking but little stain (Fig. 183). This zone consists of the recently deposited organic part of the matrix not as yet impregnated with calcareous material. The zone nearer the enamel organ will be found, by contrast, very intensely stained. This is the older part of the dentine matrix which has had the organic framework impregnated with calcareous material.
As the odontoblasts continue to secrete additional dentine matrix the accumulation of their own product inevitably forces the cell
310
DEVELOPMENT OF FACE, JAWS AND TEETH
layer back, away from the material previously deposited. Apparently
strands of their cytoplasm become embedded in the material first laid
down and are then pulled out to form the characteristic processes of
the odontoblasts known as the dentinal fibers (Fig. 183). As the layer
of secreted material becomes thicker and the cells are forced farther
from the material first deposited, these dentinal fibers become progressively longer. Even in adult teeth where the dentine may be as much
as 2 mm. in thickness they extend from the odontoblasts which line
the pulp chamber to the very outer part of the dentine. These dentinal
fibers are believed to be concerned with maintaining the organic
portion of the dentine matrix in a healthy condition. When the pulp
is removed from a tooth, taking with it the odontoblasts, we know
that the dentine undergoes degenerative changes which involve,
among other things, increase in brittleness. This would seem to be
attributable to the degeneration of the organic framework of a matrix
no longer nourished by the odontoblasts.
Formation of Enamel. While the dentine is being laid down by the cells of the odontoblast layer, the enamel cap of the tooth is being formed by the ameloblast layer of the enamel organ. As was the case with the odontoblasts, the active cells of the ameloblast layer are columnar in shape and their nuclei, too, lie in the ends of the cells toward the source of supplies, in this case the small vessels in the adjacent mesenchyme (Fig. 183). The amount of organic material laid down as the framework of enamel is much less than is the case with either bone or dentine, and it is therefore more difficult to make out its precise character and arrangement. It is, nevertheless, possible to see in decalcified sections, delicate fibrous strands projecting from the tips of the ameloblasts into the areas of newly formed enamel (Fig. 183). It seems probable that these strands {Tomes processes) are in some way involved in the formation of the organic matrix of enamel. The problem of tracing the relations of Tomes’ processes to the organic framework of enamel is greatly complicated by the fact that where the ameloblasts have deposited calcium compounds the calcium has rendered the organic part of the matrix so avid in its affinity for stains that it is not possible to discern fine structural details because of the very density of the resulting coloration (Fig. 183). This reaction of the tissue to stains persists even after the inorganic calcium compounds have been removed by decalcification, indicating that the organic framework itself has been chemically altered by the calcium deposited in it.
THE DEVELOPMENT OF THE TEETH
311
In spite -of these difficulties in getting at the exact nature and
arrangement of the organic matrix of enamel, it is quite possible to
see the genesis of its fundamental prismatic structure. Each amcloblasl
builds up beneath itself a minute rod or prism of calcareous material.
These prisms are placed with their long axes approximately at right
angles to the dento-enamel junction. Collectively these enamel prisms
form an exceedingly hard cap over the crown of the tooth which in
its structural arrangement suggests a paving of polygonal bricks laid
on end. There is sufficient difference in the rate at which the different
growth lines
in enamel
pulp chamber
growth lines in dentine
root canal
cementum
oral epithelium
osteolilasts
of periosteum of alveolus
connective
tissue ftbers
cementoblasts
( from
dental sac)
blood vessels
and nerves to pulp
Fig. 184. Schematic diagram showing the topography of a tooth and its
relations to the bone of the jaw. The numbered zones indicate empirically
the sequence of deposition of the dentine and enamel. The so-called growth
lines in the dentine and enamel follow the general contours indicated by
the dotted lines in the figure but arc much more numerous.
312
DEVELOPMENT OF FACE, JAWS AND TEETH
ameloblasts work so that in actively growing enamel the surface is
jagged and irregular due to the varying extent to ^<^hich the different
prismatic elements have been calcified (Fig. 183).
Both enamel formation and dentine formation begin at the tip of the crown and progress toward the root of the tooth (Figs. 182 and 184). But the entire crown is well formed before the root is much more than begun. The progressive increase in the length of the root is an important factor in the eruption of the tooth, for as the root increases in length the previously formed crown must move closer to the surface of the gum. Even when the crown of the tooth begins to erupt the root is still incomplete, and it does not acquire its full length until the crown has entirely emerged.
The Formation of Cementum. The so-called cementum of the tooth is virtually a bone encrustation of its root. No cementum is formed until the tooth has acquired nearly its full growth and its definitive position in the jaw. But the first indications of specialization in the tissue destined to give rise to it can be seen long before the cementum itself appears.
Outside the entire tooth germ, between it and the developing bone of the jaw, there occurs a definite concentration of mesenchyme. The concentration becomes evident first at the base of the dental papilla and extends thence crownwards about the developing tooth, which it eventually completely surrounds.
This mesenchymal investment is known as the dental sac (Fig. 182). In the eruption of the tooth the portion of the dental sac over the crown is destroyed, but the deeper portion of the sac persists and becomes closely applied to the growing root. At about the time the tooth has acquired its final position in the jaw, the cells of the dental sac begin to form the cementum. Histologically and chemically cementum is practically identical with subperiosteal bone. When we consider the manner of origin of the dental sac and of the periosteum of the bone socket (alveolar socket) in which the root of the tooth lies, and see how they arise side by side from the same sort of tissue, this seems biit natural. The dental sac is essentially a layer of periosteal tissue facing the root of the tooth and back to back with the periosteal tissue of the alveolar socket (Fig. 182).
The Attachment of Tooth in the Jaw. The attachment of the tooth in its socket is brought about by the development, between the dental sac and the periosteum of the tooth socket, of an exceedingly tough fibrous connective tissue. As the periosteum of the alveolus
THE DEVELOPMENT OF THE TEETH
313
adds new lamellae of bone to the jaw on the one side, and the dental
sac adds lamellae of cementum to the root of the tooth on the other,
the fibers of this connective tissue are caught in the new lamellae.
Thus the tooth comes to be supported by fibers which are literally
calcified into the cementum of the tooth at one end and into the bone
of the jaw at the other (Fig. 184). The mechanism involved is precisely
the same as that which occurs in the burying of tendon fibers in a
growing bone, where the buried ends of the fibers are known as the
penetrating fibers of Sharpey.
Replacement of Deciduous Teeth by Permanent Teeth. The
replacement of the temporary or “milk†(deciduous) dentition by the permanent teeth is a process which varies in detail for each tooth. The general course of events is, however, essentially similar in all cases. The enamel organ of the permanent tooth arises from the dental ledge near the point of origin of the corresponding deciduous tooth (Fig. 180). With the disappearance of the dental ledge, the permanent tooth germ comes to lie in a depression of the alveolar socket on the lingual side of the developing deciduous tooth (Fig. 185).
When the jaws approach their adult size the hitherto latent primordia of the permanent teeth b<-gin to go through the same histo
Fio. 185. Photomicrograph (X 5) of upper jaw of 160 mm. pig embryo
showing the milk cuspids just breaking through the gum.
314
DEVELOPMENT OF FACE, JAWS AND TEETH
Fig. 186. Photomicrograph (X 6) of section through the jaw of a puppy showing a deciduous tooth nearly ready to drop out and the developing permanent tooth deeply embedded in the jaw below it. The space about the crown of the permanent tooth was occupied in the living condition by enamel. Fully formed enamel, being approximately 97 per cent inorganic in composition, is almost completely destroyed by the decalcification with acids which must be carried out before such material can be sectioned. (From a preparation loaned by Dr* S. W. Chase.)
THE DEVELOPMENT OF THE TEETH
315
genetic changes we have already traced in the case of the temporary
teeth. As the permanent tooth increases in size, the root of the deciduous tooth is resorbed and the permanent tooth comes to lie underneath
its remaining portion (Fig. 186). Eventually nearly the entire root
of the deciduous tooth- is destroyed and its loosened crown drops out,
making way for the eruption of the corresponding permanent tooth.
BiLlio grapky
Although this docs not purport to be a complete bibliography
on the development of the pig, I have tried to make it comprehensive.
At least one reference has been included on every phase of the subject
concerning which I could find published information. Under each
of the main subject headings some of the articles referred to have
extensive bibliographies of the literature in their special field. But,
with the exception of a few outstanding contributions, no papers have
been included which are merely of historical interest. For such articles
reference should be made to the exhaustive bibliographies compiled
by Minot (1893) and by Keibel (1897). Furthermore, the list is largely
restricted to contributions based directly on pig embryos. Exception
to this rule has been made in favor of a few general articles which
are of especial assistance in acquiring a perspective on some phase of
the subject. Also, a number of articles based on other forms have been
included when no work appeared to have been done on corresponding
phases of development in the pig. It is hoped that such a list of
selected references will furnish a starting point for following up any
desired line of inquiry without involving one in a discouraging
multiplicity of titles.
Texts and Manuals
Arey^ L. i?., 19^6. Developmental Anatomy. Saunders, Philadelphia, 5th Ed., ix &
616 pp.
Baumgartner, W, J,, 1924, Laboratory Manual of the Foetal Pig, Macmillan, New York, vii & 57 pp.
Boyden, E. A., 1936. A Laboratory Atlas of the 13-mm. Pig Embryo. (Prefaced by younger stages of the chick embryo.) The Wistar Institute Press, Philadelphia, iv & 104 pp.
Hamilton, W. J., Boyd, J. D., and Mossman, H. W., 1945. Human Embryology.
Williams and Wilkins, Baltimore, viii & 366 pp.
Hertwig, O., 1901-07. Handbuch der Vergleichenden und experimentellen Entwicklungslehre der Wirbeltiere. (Edited by Dr. Oskar Hertwig and written by numerous collaborators.) Fischer, Jena.
Huettner, A, F., 1941. Fundamentals of Comparative Embryology of the Vertebrates. Macmillan, New York, xiv & 416 pp,
Jordan, H. E,, and Kindred, J. E., 1948. A Textbook of Embryology. Appleton, New York, 5th Ed., xiv & 613 pp.
317
318
BIBLIOGRAPHY
Keihel^ F., 1897. Normentafeln zur Entwicklungsgeschichte der Wirbelthiere. I. Des
Schweines. Fischer, Jena, 114 S.
Martin^ P., 1912. Lehrbuch der Anatomic der Haustiere. ^chickhard & Ebner, Stuttgart. (Bd. 1, Allgemeine und vergleichende Anatomic mit Entwicklungsgeschichte, xii & 811 S.)
Minot ^ C, S., 1893. A Bibliography of Vertebrate Embryology. Memoirs, Boston Soc. Nat. History, Vol. 4, pp. 487-614.
Mtnot, C, S., 1911. A Laboratory Textbook of Embryology. The Blakiston Company, Philadelphia, 2nd Ed., xii & 402 pp.
Needham^ J'., 1931. Chemical Embryology. Macmillan, New York, xxii & 2021 pp.
Patten^ B. A/., 1929. Early Embryology of the Chick. The Blakiston Company, Philadelphia, 3rd Ed., xiii & 228 pp.
Patten, B. M., 1946. Human Embryology. The Blakiston Company, Philadelphia, XV & 776 pp.
Stssori, S., 1921. The Anatomy of the Domestic Animals. Saunders, Philadelphia, 2nd Ed., 930 pp.
Wetss, P.y 1939. Principles of Development. A Text in Experimental Embryology. Holt, New York, xix & 601 pp.
IVieman, H. L., 1930. An Introduction to Vertebrate Embryology. McGraw-Hill, New York, xi & 411 pp,
Windle, W, F., 1940. Physiology of the Fetus. Saunders, Philadelphia, xiii & 249 pp.
Zeitzschmann, 0,, 1923-24. Lehrbuch dcr Entwicklungsgeschichte der Haustiere. R. Schoetz, Berlin, 542 S,
General Articles and Articles of Significance for the Interpretation of Developmental Processes
Alexander, J., 1944. The Gene — A Structure of Colloidal Dimensions. Chapt. 37, pp. 808-819, in “Colloid Chemistry,†Vol. V, edited by Jerome Alexander, Reinhold Publishing Corp., New York.
Allen, W. F., 1918. Advantages of sagittal sections of pig embryos for a medical embryology course. Anat. Rec., Vol. 14, pp. 183-191.
Barth, L. G., 1944. Colloid Chemistry in Embryonic Development. Chapt. 39, pp. 851-859, in “Colloid Chemistry,†Vol. V, edited by Jerome Alexander, Reinhold Publishing Corp., New York.
Chambers, R., 1944. Some Physical Properties of Protoplasm. Chapt. 41, pp. 864-875, in “Colloid Chemistry,†Vol. V, edited by Jerome Alexander, Reinhold Publishing Corp., New York.
Conklin, E, G., 1914. The cellular basis of heredity and development. Pop. Sci. Monthly, Vol. 85, pp. 105-133. '
Hartman, C. G., 1 931 . Development of the egg as seen by the physiologist. Sci. Monthly, Vol, 33, pp, 17-28.
Medley, 0. F., 1926. Quantitative study of growth of certain organs in pig fetus. Bull. Med. Coll. Va., Vol. 23, pp. 19-36.
Holtfreter, J., 1947. Changes of structure and the kinetics of differentiating embryonic cells. Jour. Morph., Vol. 80, pp. 57-92.
Holtfreter, J., 1947. Observations on the migration, aggregation and phagocytosis of embryonic cells. Jour. Morph., Vol. 80, pp. 93-111.
THE SEX ORGANS AND GAMETOGENESIS
319
Kingsbury, B. F,, 1926. On the so-called law of anteroposterior development. Anat.
Rec., Vol. 33, pp. 73-87.
Lewis, W, H., 1947. Mechanics of invagination. Anat. Rec., Vol. 97, pp. 139-156.
Spemann, H., 1927. Organizers in animal development. Proc. Roy. Soc. London, Ser. B, Vol. 102, pp. 177-187.
Spemann, H., 1938. Embryonic Development and Induction. Yale Univ. Press, New Haven, xii & 401 pp.
The Sex Organs and Gametogenesis
Allen, E., 1923. Ovogenesis during sexual maturity. Am. Jour. Anat., Vol. 31, pp. 439-481.
Allen, E., Kountz, IV. B., and Francis, B. F., 1925. Selective elimination of ova in the adult ovary. Am. Jour. Anat., Vol. 34, pp. 445-468.
Bascom, K. F., 1925. Quantitative studies of the testis. I. Some observations on the cryptorchid testes of sheep and swine. Anat. Rec., Vol. 30, pp. 225-241.
Bascom, K. F., and Ouerud, H. L., 1925. Quantitative studies of the testicle. II. Pattern and total tubule length in the testicles of certain common mammals. Anat. Rec., Vol. 31, pp. 159-169.
Blandau, R. J., 1945. The first maturation division of the rat ovum. Anat. Rec., Vol. 92, pp. 449-457.
Corner, G. W., 1917. Maturation of the ovum in swine. Anat. Rec., Vol. 13, pp. 109 112 .
Comer, G. IV., 1919. On the origin of the corpus luteum of the sow from both granulosa and theca interna. Am. Jour. Anat., Vol. 26, pp. 117-183.
Evans, H. M., and Swezv, 0., 1929. Ovogenesis and the normal follicular cycle in adult mammalia. Mem. LTniv. Cal., Vol. 9, pp. 119-224.
Everett, N. B., 1945. The present status of the germ-cell problem in vertebrates. Biol. Rev., Vol. 20, pp. 45-55.
Gould, H. N., 1923. Observations on the genital organs of a sex intergrade hog. Anat. Rec., Vol. 26, pp, 241-261.
Hargitt, G. T., 1925-30, The formation of the sex glands and germ cells of mammals. Jour. Morph. & Physiol., Vols. 40, 41, 42, 49.
Hartman, C. G., 1926. Polynuclear ova and polyovular follicles in the opossum and other mammals, with special reference to the problem of fecundity. Am. Jour. Anat., Vol. 37, pp. 1-52.
Hill, R. T., Allen, E., and Kramer, T. C., 1935. Cinemicrographic studies of rabbit ovulation. Anat. Rec., Vol. 63, pp. 239-245.
Kellicott, W. E,, 1913. A Textbook of General Embryology. Holt, New York, v & 376 pp.
Kiipfer, M., 1920. Beitrage zur Morphologic der weiblichen Geschlechtsorgane bei den Saugetieren. Ueber das Auftreten gelber Korper am Ovarium des domestizierten Rindes und Schweines. Vierteljahrsschrift d. Naturf. Gesellsch., Zurich, Bd. 65, S. 377-433.
Latta, J, S., and Pederson, E. S,, 1944. The origin of ova and follicle cells from the germinal epithelium of the ovary of the albino rat as demonstrated by selective intravital staining with India ink. Anat. Rec., Vol. 90, pp. 23-35,
320
BIBLIOGRAPHY
Morgan^ T. H.j 1926. The Theory of the (iene. Yale Univ. Press, New Haven, xvi &
343 pp.
Fainter, T. S,, 1922. Studies in mammalian spermatogenesis. J(/Ur. Exp. Zodl., Vols. 35, 37, 39. Jour. Morph. & Physiol., Vol. 43.
Parker, G. H., and Bullard, C., 1913. On the size of litters and the number of nipples in swine. Proc, Am. Acad. Arts & Sciences, Vol. 49, pp. 399-426.
Patten, W., 1925. Life, evolution and heredity. Sci. Monthly, Vol. 21, pp. 122-134.
Pincus, G., and Enzrnann, K. V,, 1937. The growth, maturation and atresia of ovarian eggs in the rabbit. Jour. Morph., Vol. 61, pp. 351-383.
Pltske, E. C., 1940. Studies on the influence of the zona pellucida in atresia. Jour. Morph., Vol. 67, pp 321-349.
Schmaltz-, B., 1911. Die Slrucktur der Ge.schlechtsorgane der ITaussaugetiere. P. Parey, Berlin, xii & 388 S.
Smith, J, T., and Kettcrmgharn, R. C., 1937-38. Rupture of the graafian follicles. Part I. Am. Jour. Obs. & Gyn., Vol. 33, pp. 820-827. Part IT Am. Join. Obs. & Gyn., Vol. 36, pp. 45.3-460.
Stein, K. F., and Allen, E., 1942. Attempts to stimulate proliferaticm of the germinal epithelium of the ovary. Anat. Rec., Vol. 82, pp. 1 -9.
Thanhoffer, L. de, 1934. The structure of the graafian follicle as revealed by microdissection. Zeilschr. f. Anat. u. Entwg., Bd. 102, S. 402-408.
Warwick, B. L., 1925. The eflect of vasectomy on swine. Anat. Rec., Vol. 31, pp. 19-21.
Wihon, E. B., 1925. The Cell in Development and Heredity. Macmillan, New York, 3rd Ed., ix & 1232 pp.
Young, W. C , 1929. A study of the function of the epididymis. I. Is the attainment of full spermatcjzoon maturity attributable to some specific action of the epididymal secretion? Jour. Morph. & Physiol., Vol. 47, pp. 479-495.
Young, W. C., 1929. A study of the function of the epididymis. II. The importance of an aging process in sperm for the length of the period during which fertilizing capacity is retained by sperm isolated in the epididymis of the guinea-pig. Jour. Morph. & Physiol., Vol. 48, pp. 475-491.
Young, W. C., 1931. A study of the function cT the epididymis. III. Functional changes undergone by spermatozoa during their passage through the epididvmis and vas deferens in the guinea-pig. Jour. Exp. Biol., Vol. 8, pp. 151-162.
The Sexual Cycle, Fertilization, Sex Determination
Allen, E., 1926. The ovarian follicular hormone: a study of variation in pig, cow, and human ovaries. Proc. Soc. Exp. Biol. & Med., Vol. 23, pp. 383-387.
Allen, E,, Danforth, C. H., and Daisy, ErA,, 1939. Sex and Internal Secretions. Williams and Wilkins, Baltimore, 2nd Ed., xxxvi & 1346 pp.
Allen, E., and Daisy, E. A., 1927. Ovarian and placental hormones. Physiol. Reviews, Vol. 7, pp. 600-650.
Ampolsky, Z)., 1928. Cyclic changes in size of muscle fibers of the fallopian tube of the sow. Am. Jour. Anat., Vol. 40, pp. 459-469.
Blandau, R., and Money, W. L., 1944. Observations on the rate of transport of spermatozoa in the female genital tract of the rat. Anat. Rec., Vol. 90, pp. 25.5-260.
THE SEXUAI, CYCLE, FERTILIZATION, SEX DETERMINATION 321
Burns, R. K., Jr., 1938. Hormonal control of sex differentiation. Am. Nat., Vol. 72,
pp. 207-227.
Comstock, R. E., 1939. A study of the mammalian sperm cell. I. Variations in the glycolytic power of spermatozoa and their relation to motility and its duration. Jour. Exp. Zool., Vol. 81, pp. 147—164.
Corner, G. W., 1915. The corpus luteum of pregnancy as it is in swine. Carnegie Inst., Contrib. to E-mbryoL, Vol. 2, pp. 69-94.
Corner, G. W., 1917. Variations in the amount of phosphatids in the corpus luteum of the sow during pregnancy. Jour. Biol. Chem., Vol. 29, pp. 141-143.
Corner, G. W , 1919. On the origin of the corpus luteum of the sow from both granulosa and theca interna. Am. Jour. Anal., Vol. 26, pp. 117-183.
Cornet, G. W., 1921. Cyclic changes in the ewaries and uterus of swine, and their relations to the mechanism of implantaticm. Carnegie Inst., Contrib. to Embryol., Vol. 13, pp. 117-146.
Corner, G. IT., 1923. Cyclic variation in uterine and tubal contraction waves. Am. Jour. Anat., Vol. 32, pp. 345-351.
Corner, G IT., 1928. Physiolcjgy of the corpus luteum. I. The efTect of \Try early ablation of the corpus lutcnun upon embryos and uterus. Am. Jour. Physiol., Vol. 86, pp. 74-81.
Coiner, G IV., 1942. The Hormones in Human Reproduction. Princeton Univ. Press, Princeton, xix & 265 pp.
Corner, G. IT., and Allen, IT, M., 1929. Physiology of the corpus luteum. II. Production (3f a special uterine reac tion (progestational proliferation) by extracts of the cwpus luteum. Am. Jour. Physiol., Vol. 88, pp. 326-339.
Coinn, G. IT., and Allen, IT. A/., 1929. Physiology of the corpus luteum. III. Normal growth and implantation of embryos after very earlv ablation of the ovaries, under the influence of extracts of the corpus luteum. Am. lour. Physiol., Vol. 88, pp. 340-346.
Cornn, G. IT, and Amsbaugh, A. E., 1917. Oestrus and ovulation in swine. Anat. Rec., Vol. 12, pp. 287-291.
Corner, G. IT., and Snyder, F. F., 1922. Observations on the structure and function of the uterine ciliated epithelium in the pig, with reference to certain clinical hypothesep. Am. Jour. Obs. & Gyn., VcjI. 3, pp. 358-366.
Crew, F. A. E., 1925. Prenatal death in the pig and its effect upon the sex-ratio. Proc. Roy. Soc. Edinburgh, V^ol. 46, pp. 9-14.
Hammond, J., 1934. The fertilisation of rabbit ova in relation to time: A method of controlling the litter size, the duration of pregnancy and the weight of the young at birth. Jour. Exp. Biol., Vol. 11, pp. 140-161.
Hartman, C. G., 1929. The homology of menstruation. J. A. M. A., Vol. 92, pp. 19921995.
Hartman, C. G., and Squier, R. R., 1931. The follicle-stimulating effect of pig anterior lobe on the monkey ovary. Anat. Rec., Vol. 50, pp. 267-273.
Keye, J. D., 1923. Periodic variations in spontaneous contractions of uterine muscle in relation to the oestrous cycle and early pregnancy. Bull. Johns Hopkins Hosp., Vol. 34, pp. 60-63.
Lewis, L. L., 1911. The vitality of reproductive cells. Agric. Exp. Sta. Oklahoma, Bull. No. 96.
322
BIBLIOGRAPHY
Lillie^ F. /?., 1919. Problems of Fertilization. Univ. Chicago Press, xii & 278 pp.
Loeb^ Z.., 1923. The mechanism of the sexual cycle, with special reference to the corpus luteum. Am. Jour. Anat., Vol. 32, pp. 305-343. ^
Markee, J. E., Pasqualetti^ R. A., and Hinsey, J. C., 1936. Growth of intraocular endometrial transplants in spinal rabbits. Anat. R^c., Vol. 64, pp. 247-253.
Marshall^ F, H. A., 1922. The Physiology of Reproduction. Longmans, Green & Co., London, 2nd Ed., xvi & 770 pp.
McKenzie^ F. F, 1926. The normal oestrous cycle in the sow. Univ. Missouri Coll. Agric. Exp. Sta. Res. Bull., Vol. 86, pp. .S-41.
Papanicolaou^ G. A'"., 1923. Oestrus in mammals from a comparative point of view. Am. Jour. Anat., Vol. 32, pp. 285-292.
Parker^ G. IL, 1931. Passage of sperms and of eggs through oviducts in terrestrial vertebrates. Phil. Trans. Roy. Soc. London, Ser. B, Vol. 219, pp. 381-419.
Phillips, R. W., and Andrews, F, j\., 1937. The speed oi travel of ram spermatozoa. Anat. Rec., Vol. 68, pp. 127-132.
Pincus, G., 1936. The Eggs of Mammals. Macmillan, New York, ix & 160 pp.
Schott, R. G., and Phillips, R. W., 1941. Rate of sperm travel and time of ovulation in sheep. Anal. Rec,, Vol. 79, pp. 531-540.
Secktnger, D, L., 1923. Spontaneous contractions of the Fallopian tube of the domestic pig with reference to the oestrous cycle. Bull. Johns Hopkins Hosp., Vol. 34, pp. 236-239.
Snyder, F. F., 1923. Changes in the Fallopian tube during the ovulation cycle and early pregnancy. Bull. Johns Hopkins Hosp., Vol. 34, pp. 121-125.
Soderwall, A, L., and Blandau, R. J., 1941. The duration of the fertilizing capacity of spermatozoa in the female genital tract of the rat. Jour. Exp. Zool , Vol. 88, pp. 55-64.
Stockard, C. /?., 1923. The general morphological and physiological importance of the oestrous problem. Am. Jour. Anat., Vol. 32, pp. 277-283.
Surface, F. M., 1908, Fecundity of swine. Biometrika, Vol. 6, pp. 433-436.
Swingle, W, W., 1926. The determination of sex in animals. Physiol. Rev., Vol. 6,
pp. 28-61.
Toothill, M. C., and Toung, W. C.,\93\. The time consumed by spermatozoa in passing through the ductus epididymidis of the guinea-pig as determined by means of India-ink injections. Anat. Rec., Vol. 50, pp. 95-107.
Wilson, K. M., 1926. Histological changes in the vaginal mucosa of the sow in relation to the oestrous cycle. Am. Jour. Anat., Vol. 37, pp. 417-432.
Witschi, E., 1932. Physiology of embryonic sex differentiation. Am. Nat., Vol. 66, pp. 108-117.
Cleavage, Germ Layer Formation^ and the Structure of Young
Embryos
Assheton, R., 1899. The development of the pig during the first ten days. Quart. Jour. Micr. Sci., Vol. 41, pp. 329-359.
Clark, R, T,, 1934. Studies on the physiology of reproduction in the sheep. II. The cleavage stages of the ovum. Anat. Rec., Vol. 60, pp. 135-159.
Conklin, E, G., 1909. The application of expieriment to the study of the organization and early differentiation of the egg. Anat. Rec., Vol. 3, pp. 149-154.
CI.EAVAGE, GERM LAYERS, YOUNG EMBRYOS
323
Defrise^ A.^ 1933. Some observations on living eggs and blastulae of the albino rat.
Anat. Rec., Vol. 57, pp. 239-250.
Green^ W, W., and Winters, L. Af., 1946. Cleavage and attachment stages of the pig. Jour. Morph., Vol. 78, pp. 305-316.
Heuser, C\ H., and Streeter, G. L., 1 929. Early stages in the development of pig embryos, from the period of initial cleavage to the time of the appearance of limb-buds. Carnegie Inst., Contrib. to Embryol., Vol. 20, pp. 1-29.
Keibel, F., 1891. Uebcr die Entwicklungsgeschichte des Schweines. Anat. Anz., Bd. 6, S. 193-198.
Keibel, F., 1894. Studien zur Entwicklungsgeschichte des Schweines (Sus scrofa domesticus). I. Morph. Arbeiten, Bd. 3, S. 1-139.
Keibel, F., 1895. Ueber einige Plattenmodelle junger Schwein-embryonen. Verhandlungen d. Anat. Ges., Erganzungsheft Bd. 10, Anat. Anz., S. 199-201. Keibel, F., 1896. Studien zur Entwicklungsgeschichte des Schweines (Sus scrofa domesticus). II. Morph. Arbeiten, Bd. 5, S. 17-168.
Kingsbury, B, F., 1920. I'he developmental origin of the notochord. Science, N. S., Vol. 51, pp. 190-193.
Kingsbury, B. F., 1924a. The developmental significance of the notochord (Chorda dorsalis). Zeitschr. f. Morphologic u. Anthropologic, Vol. 24, pp. 59-74. Kingsbury, B. F,, 1924b. The significance of the so-called law of cephalocaudal differential growth. Anat. Rec., Vol. 27, pp. 305-321.
Kingsbury, B, F., 1926. On the so-called law of antero-posterior development. Anat. Rec., Vol. 33, pp. 73-87.
Lewis, F. T., 1902. The gross anatomy of a 12-mm. pig. Am. Jour. Anat., Vol. 2,
pp. 211-226.
Lewis, W, H,, and Gregory, P. W,, 1929. Cinematographs of living developing rabbiteggs. Science, Vol. 69, pp. 226-229.
Lewis, W. H., and Hartman, C, G., 1933. Early cleavage stages of the egg of the monkey (Macacus rhesus). Carnegie Inst., Contrib. to Embryol., Vol. 24, pp. 187-201. Lewis, W. PL, and Wright, E, S,, 1935. On the early development of the mouse egg.
Carnegie Inst., Contrib. to Embryol., Vol. 25, pp. 113-144.
Macdonald, E., and Long, J, A., 1934. Some features of cleavage in the living egg of the rat.^Am. Jour. Anat., Vol. 55, pp. 343-361.
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The Ductless Glands
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Connective Tissues, Skeletal, and Muscular Systems
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Teeth, Hair, and Hoofs
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Twins, Double Monsters, Anomalies
Baumgartner, W, J,, 1928. A double monster pig — Cephalothoracopagus monosymmetros. Anat. Rec., Vol. 37, pp. 303-316.
Berge, S,, 1941. The inheritance of paralysed hind legs, scrotal hernia and atresia ani in pigs. Jour. Heredity, Vol. 32, pp. 271-274.
340
BIBLIOGRAPHY
Bishopy Af., 1921. The nervous system of a two-headed pig embryo. Jour. Comp.
Neur., Vol. 32, pp. 379-428.
Bishops M., 1923. The arterial system of a two-headed pig embfyo. Anat. Rec., Vol. 26, pp. 205-222.
Carey, E,, 1917. The anatomy of a double pig, Syncephalus thoracopagus, with especial consideration of the genetic significance of the circulatory apparatus. Anat. Rec., Vol. 12, pp. 177-192.
Chidester, F. /?., 1914. Cyclopia in mammals. Anal. Rec., Vol. 8, pp. 355-366.
Cornel, G, W., 1921. Abnormalities of the mammalian embryo occurring before implantation. Carnegie Inst., Contrib. to Embryol., Vol. 13, pp. 61-66.
Corner, G. W., 1922. The morphological theory of monochorionic twins as illustrated by a series of supposed early twin embryos of the pig. Bull. Johns Hopkins Hosp., Vol. 33, pp. 389-392.
Corner, G. W., 1923. The problem of embryonic pathology of mammals with observations upon intra-uterine mortality in the pig. Am. Jour. Anat., Vol. 31, pp. 523-545.
Denison, H., 1908. Notes on pathological changes found in the embryo pig and its membranes. Anat. Rec., Vol. 2, pp. 253-256.
Dutta, S. K., 1930. Notes on the cyclopian eye and other deformities of the head in a pig. (Sus cristatus Wagn.) Allahabad Univ. Studies, Sci. Sec., Vol. 7, pp. 53-103.
Fitzpatrick, F, L,, 1928. The dissection of an abnormally developed foetal pig, with notes on the possible origins of such “freaks.†Proc. Iowa Acad. Sci., Vol. 35, pp. 319-325.
Hughes, W., 1927. Sex-intergrades in foetal pigs. Biol. Bull., Vol. 52, pp. 121-136.
Jordan, H. E., Davis, J. S., and Blackford, S. D., 1923. The operation of a factor of spatial relationship in mammalian development, as illustrated by a case of quadruplex larynx and triplicate mandible in a duplicate pig monster. Anat. Rec., Vol. 26, pp. 311-318.
Kingsbury, B, F., 1909. Report of a case of hermaphroditism (H. Verus lateralis) in Sus scrofa. Anat. Rec., pp. 278-281.
Nordby, J. E., 1929. Congenitad skin, ear, and skull defects in a pig. Anat. Rec., Vol. 42, pp. 267-280.
Poklman, A, G., 1919. Double ureters in human and pig embryos. Anat. Rec., Vol. 15, pp. 369-373.
Schwalbe, E., 1906-1913. Die Morphologic dcr Missbildungen des Menschen und der Tiere. Fischer, Jena, Vol. 1, xvi & 230 pp., Vol. 2, xx & 410 pp., Vol. 3, Abt. 1, 270 pp., Abt. 2, 858 pp., Anhang, 266 pp.
Streeter, G. L., 1924. Single-ovum twins in the pig. Am. Jour. Anat., Vol. 34, pp. 183-194.
Thuringer, J, M,, 1919. The anatomy of a diccphalic pig (Monosomus diprosopus). Anat. Rec., Vol. 15, pp. 359-367.
JVarkany, J., and Roth, C, B., 1948. Congenital malformations induced in rats by maternal vitamin A deficiency. II. Effect of varying the preparatory diet upon the yield of abnormal young. Jour. Nutrition, Vol. 35, pp* 1-11.
Williams, S. R., and Rauch, R. W., 1917. The anatomy of a double pig (Syncephalus thoracopagus). Anat. Rec., Vol. 13, pp. 273-280.
Index
To facilitate the use of this book in connection with otheis in which the terminology
may differ somewhat, many synonyms which were not used in the text have been put into
the index and cross-referenced to the alternative terms used in this book; for example,
Wolffian body, a teim not used in this text, is frequently applied to the mesonephros. It
appears m the index thus: Wolffian body (= mesonephros, q.v.).
Both figure and page references are given in the index. The figure references arc preceded by the letter /.
Abdominal pregnancy, 217
Abducens nerve, 169
Accessory nerve, 172
Acoustic ganglion, /92, 117, 169
Acoustico-facialis ganglion ( = early undifferentiated condition of ganglia of
7th and 8th cranial nerves), 169
Action system, 141
Adrenal, /1 00, /106, /1 27, /1 28, /1 38, 223 After-birth, 105 Alae of nose, 296 Alar plate of neural tube, 1 57 Allantois, circulation of, /45,/51, 99 formation of,/30,/37, 99 function of, 106 relations of,/49,/55, 103 Alveolar periosteum, 312 Ameloblasts,/179-183, 305, 310 Amnion, formation of,/25,/37,/50, 97 function ofi 96 relations of,/49, 97 Amniotes, 96 Amniotic folds, 97 Ampulla of ductus deferens, /3, 8 Anal plate ( = cloacal plate, q.v.) Anamniotes, 96 Angioblast, 87 footnote Animad pole, 37
Anterior intestinal portal, /37, 74 Anterior neuropore, /29, 71 Anus,/118,/132, 210, 225 Aorta, see arteries Aortic arches, sec arteries Aortic bulb, 256 Aortic chromaffin body, 223 Appendage buds, /3 1-34, 65, 109
Appendix, of epididymis, /1 24, 213
of testis, /1 24, 217
Appositional growth, 278
Aqueduct of Sylvius, 158
Archenteron, 43
Areola, 105
Arterial circle (of Willis), 131 Arteries, allantoic, /45,/51, 89, 132, 240 aorta, dorsal, /67, /1 33-1 37, 88, 131, 235, 240
aoita, ventral, /45, /1 33, 88, 235 aortic arches, /45, /1 33-1 37, 88, 129,
233
basilar, /66, /67, /133, /137, 131, 238 brarhio-cephalic,/133, 234 carotid, common, /1 33, /1 37, 234 carotid, external, /67, /1 33, /1 37, 130,
234
carotid, internal, /66, /133, /137, 130, 234, 238 caudal, 240
cervical, intersegmental,/66,/133,/l37, 130, 235
coeIiac,/67,/lll, 132, 240 ductus arteriosus /1 33, /ISO, 235, 262, 268
hypogastric, 240, 270 iliacs,/66, /150, 240 innominate, 234 internal mammary, 238 interscgmcntal,/67,/133, 130, 235 mesenteric, ant., /67, /1 11, 132, 238 mesenteric, post»,/lll, 238 omphalomesenteric, /45, 89, 131, 238 pulmonary, /67, /1 33-1 37, 130, 234, 267
341
342
INDEX
Arteries — {Continued)
renal, /1 27, /1 28, 240 speimatic, /1 27-1 30
subclavian, /67, /133-135, 131, 234, 235
umbilical (allantoic), /66, /1 50, 89, 132, 240
vertebral,/66,/67,/137, 131, 237 vitelline, /45, 89, 132 Arytenoid process of larynx, /1 38 Astrocytes, 150 Atresia of ovarian follicles, 20 Atrio-ventricular canal, 126, 256 Atrium, 126, 254
Auditory, ganglion, see acoustic nerve, 1 69 vesicle, /36,/61, 117, 169
Basal plate of neural tube,/91, 157 Belly-stalk, /49, 97 Bicornate uterus, 216 Bile duct, common, 185 Bladder (urinary), /118, /124, /125, /130, 209
Blastocoele, j\S, 41 Blastocyst, /1 7, 41
elongation of, /1 8, 45 riastodermic vesicle ( == blastocyst, q.v.) Blastodisc ( — embryonic disc, q.v.) Blastorneie, 38 Blastula, 41
Blood cells, formation of,/48,/152, 90, 251 Blood islands, /48, 89, 251 Blood vessels, formation of, /48, 87 see also arteries and veins Body axis, 60 Body cavity, see coelom Body folds, /38, 72 Body-stalk, sec belly-stalk Bone, cancellous, 272 cells, /1 51, /1 52, 275 compact, 272 endochondral, 272 histogenesis of, 271 intramembranous, 272 lacuna, 275 lamellae, /1 51, 275 marrow, /1 52, 251 matrix, /1 51, 273 trabeculae, /1 51, /1 53, 274 Bone, formation of,
compact from cancellous, 281
Bone — '{Continued)
endochondral, /1 55, 276 flat, /1 57, 282 '
intramem branous, /1 5 1 , /1 53, 272 long, /1 58, 283
primary cancellous, /1 51, /153, 272, 281
Bowman’s capsule, /1 16, 203 Brachial plexus, 116 Brain, formation of, /36, 69 neuromeric structure of, 69 regional differentiation of,/87, 1 S4 ventricles of, /88, 156, 160 3-vesicle stage, /36, 70 5-vesicle stage, /60, 110 Branchial arches (= gill arches, q.v.)
Bridge of nose, 296
Broad ligaments of uterus, 222
Bronchi, 189
Bulbo-urethral gland, /3, /1 24, 9, 213
Clalcification
of bone, 274 of teeth, 309
Calyces of renal pelvis, /1 19 Canal, atrio-ventncular, 126 Haversian, /1 56, 282 inguinal, /1 29, 222 of Gartner, 217 pleural,/! 10 pleuro- peritoneal, 195 semicircular, 169 Canalicuii, /152 Cancellous bone, /1 53, 276 Capsule, glomerular, /1 21, 203 of Bowman, /1 21 , 203 of cartilage cells, 278 Cardiac loop, /1 42, 125, 254 Cardinal vessels, see veins “Cartilage bone,†272 Cartilage, erosion, /1 55, 280 formation, /1 54, 277 matrix, 278 Caval plica, /1 40, 245 Cecum, /102, 122, 182 Cementoblasts, /1 84 Cemcntum,/184, 312 Central canal of spinal cord,/86, 151 Centrum, see vertebrae Cephalic region, differentiation of, 61 mesoderm of, 1 91
INDEX
343
Cephalic region — (Continued)
precocity of, 54
Cerebellar peduncles, 157
Cerebellum, /80,/87, 157
Cerebral aqueduct, 158
Cerebral cortex, 145, 162
Cerebral ganglia, see ganglia, cranial
Cerebral hemispheres, /87, 162
Cerebral peduncles, /1 00, 158
Cerebro-spinal paths, 142
Cervical flexure, 66
Cervical sinus, /32, /1 69, 109
Cervix of uterus, 216
Choanae, of nose, 296
Chondrin, 278
Chondrogenesis, 276
Chondrogenctic layer, 278
Chorda dorsalis ( = notochord, q.v.)
Chorion, /55-57, 103 Chorionic vesicle, /54, 103 Chorionic villi, /57 Choroid fissure, of eye,/39, 117 Choroid plexus, anterior (of 3rd ventricle), /106, 158, 162
lateral (of 1st and 2nd ventricles), /1 00.
162
posterior (of 4th ventricle), /65, /99, /1 38, 156
Chromaffin tissue, 223 Chromosomes, sex, 23 species number of, 21 Circle of Willis, /1 33, 131 Circulation, changes in at birth, 268 early embryonic, /45,/51, 92 hepatic portal, 241 interpreta^tion of embryonic, 227 placental,/45,/51,/55, 93, 263 pulmonary, 262, 267 vitelline, /45, /1 41, 93, 249 Circulatory arcs, 92 Cleavage, /1 2, /1 3, /1 4, 37 Cleavage cavity, see blastococle aitoris,/132, 225 Cloaca, /65, /1 18, 120, 209 Cloacal plate (membrane), /37, 209 Cochlea, 169 Coelom, /1 09
abdominal, /1 11, 194 diflferentiation of, /1 08, 193 formation of,y20, f22,/108, 51, 120, 189 intra- and extra-embryonic, 52, 190
Coelom — (Continued)
partitioning of, /1 11-1 13, 194 pericardial, /26, /44, /1 09, /1 10, /111, 53, 87, 195 peritoneal, /1 10, 189 pleural,/! 11, /1 13, 194 thoracic, 194
Colliculi, inferior, suptTior (lobes of corpora quadngemma), /80, /87, 157, 167 Colon (large intestine), /1 02, 182 Columns of spinal cord, /8 6, 154 Commissural ganglion, /92, 172 Components of spinal nerve, 151 Concrescence, /20, 46 Coordinating centers, 145 Copula, /41 Cord, spinal, 71, 115
and reflexes, /80, 142 histogenesis of, /8 1-8 3, 147 white and grey matter of,/86, 151 Cord, umbilical, 250 Corona radiata, 18 Coronary sinus, sec veins Corpora quadrigemma, /87, 157 Corpus albicans, 27 Corpus hacmorrhagicurn, 26 Corpus luteum, formation of,/6, 24 in pregnancy, /1 0, 26 significance of, 33 Corpus striatum, 1 63
Cowper’s gland (= bulbo-urethral gland, q.v.)
Cranial flexure, 66
Cranial ganglia, see ganglia
Cranial nerves, see nerves
Crura cerebri (= cerebral peduncles, q.v.)
Cumulus oophorus, 19
Cutis plate, see dermatome
Cystic duct,/104,/105, 184
Decalcification, 274 Deciduous placenta, 103 Deitcr’s nucleus, /80, 144 Dental ledge, /1 75-1 80, 302 Dental papilla, 307 Dental sac, /1 82, 312 Dentinal fiber /1 83, 310 Dentine, /1 83, 307 Dermatome, /42, 81
Deutoplasm, effect of on cleavage, /1 2, 37 in pig ovum, 39
344
INDEX
Diaphragm, /1 00, /1 12, 194
Diaphragmatic ligament of mesonephros,
/1 23, 218
Diaphysis, of long bone, 283 Dicnccphalon, /60, 110, 158 Diestrum, 29
Diocoele ( =« lumen of diencephalon) Dio-mesencephalic boundary, 110 Dio-telcncephalic boundary, 110 Diploe, of bone, 282 Diploid number of chromosomes, 22 Dorsal, aorta, see arteries flexure, 66
mesentery, /1 08, /1 11, 192 mesocardium,/43,/144, 87, 254 nerve roots, see nerves, spinal root ganglia, see ganglia, spinal Duct of, Cuvier ( = common cardinal vein, q.v.)
Santorini, 186 Wirsung, 186
Ductus, arteriosus, /1 33, /1 38, /1 50, 235, 262, 268
choledochus ( = common bile duct, q.v.) deferens, /3, /1 18, /1 24, 9, 213 endolymphaticus, 117 venosus, see veins Duodenum, /1 00, /1 02, 184
Ear, external, /33,/34, 62 internal, 62, 117, 169 middle, 118, 170 Ectoderm, 59, 98
derivatives of,/27 Efferent ductules, 213 Egg nests, 1 5
Ejaculatory duct, /3, /1 24, 9, 213 Embryonic disk, /1 6, /1 9, 45, 60 Enamel, /183, 310 Enamel organ, /1 79-1 82, 303 Enamel prisms, 311
Endocardial cushion of A-V. canal, /39, /147,/148, 126, 256 Endocardial cushion tissue, 256 Endocardial primordia,/43,/44, 85 Endocardium, 85 Endolymphatic duct, 117 Endothelium, origin of vascular, /48, 87 Entoderm, 59
derivatives of, /27 formation of, /1 6, 43
Eparterial bronchus, /1 07
Ep>endymal cells, 150
Ependymal layer of c^d,/81, 147
Epicardium, 85
Epididymis, /3, /1 24, /1 29, 213
Epi-myocardium,/43,/44, 85
Epiphyseal cartilage plates, 284
Epiphyseal ossification centers, 284
Epiphyses of long bones, /1 58, 284
Epiphysis, of diencephalon, /1 06, 110, 158
Epiploic foramen, 181
Epo6phoron,/125, 217
Equation division, 22
Erythroblasts, /1 52
Esophagus, /64,/72, 80, 119, 179
Estrus, 29
Estrus cycle, /9, 29
Eustachian tube, 118, 175
Evolution, 198, 229
Exocoelom, 52
Extra-embryonic coelom, see coelom Extra-embryonic membranes, /49, 94 Eye, 63, 116, 167
Face, development of, /1 68-1 72, 293 Facial nerve, /92, 169 Falciform ligament, /1 1 1 , 193 Fallopian tube (= uterine tube, q.v.) Fasciculi, see columns of spinal cord Fertilization, /1 1, 34 Flexion, 65, 107 Floor plate of neural tube, 156 Fetal membranes, see extra-embryonic membranes
Follicle, ovarian, /6,/7, 17 Foramen, ovale, 260, 267, 268 see also interatrial
Foramen of Monro, /88, /1 38, 160 Foramen of Winslow, 181 Fore-brain, see prosencephalon Fore-gut, /26,/37, 74 Fossa ovalis, 269
Fovea cardiaca (= ant. intestinal portal, q.v.)
Frontal lobe, 163
Frontal process, /1 68-1 72, 293
Froriep’s ganglion, /92, 172
Gall-bladder, /46, /103-105, /1 40, 80, 119, 184
Gametes, /8, 9, 12, 15
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