24-hour chick embryo
24-hour chick embryo
24 hour chick embryo 24 hour chick embryo
through head fold and subcephalic space through head fold and subcephalic space
In this more caudal section, the continuity of the neural folds are evident. The outer layer of the head fold (also called the head In this more caudal section, the continuity of the neural folds are evident. The outer layer of the head fold (also called the head process) is composed of ectoderm. Below the head fold
process) is composed of ectoderm. Below the head fold note the subcephalic space, a lanote the subcephalic space, a la yer of ectoderm, and a layer of yer of ectoderm, and a layer of endoderm.endoderm.
through head fold, foregut, and notochord through head fold, foregut, and notochord At this level, sectioning has now reached the
At this level, sectioning has now reached the notochord. The notochord is evident ventral to the neural notochord. The notochord is evident ventral to the neural folds. Vfolds. Ventral to the notochord,entral to the notochord, the foregut appears as a smile-shaped cavity delimited by thin endodermally derived walls. Note that the mid portion of the floor of the foregut appears as a smile-shaped cavity delimited by thin endodermally derived walls. Note that the mid portion of the floor of the foregut is slightly thickened. Below this region is a region of slightly thickened ectoderm. This region is the oral plate which will the foregut is slightly thickened. Below this region is a region of slightly thickened ectoderm. This region is the oral plate which will become perforated at a later date to form the mouth. Below the head fold is the subcephalic space and extraembryonic germ layers. become perforated at a later date to form the mouth. Below the head fold is the subcephalic space and extraembryonic germ layers. Note the proamnion (ectoderm and endoderm) below the head fold. Lateral to
Note the proamnion (ectoderm and endoderm) below the head fold. Lateral to the proamnion, layers of mesoderm are visible betweenthe proamnion, layers of mesoderm are visible between the ectoderm and endoderm. The cavity that is evident between the
the ectoderm and endoderm. The cavity that is evident between the layers of mesoderm is the coelom.layers of mesoderm is the coelom.
through anterior intestinal portal through anterior intestinal portal
In this section, note that the neural folds have come together to form the neural tube. This section is also at the level of the open In this section, note that the neural folds have come together to form the neural tube. This section is also at the level of the open foregut. Note that the endoderm of the
foregut. Note that the endoderm of the foregut is continuous with the rest of foregut is continuous with the rest of the endoderm. The opening of the closed foregut the endoderm. The opening of the closed foregut is calledis called the anterior intestinal portal. Examine the thickened, splanchnic mesoderm on each side of
the anterior intestinal portal. Examine the thickened, splanchnic mesoderm on each side of the anterior intestinal portal. This region of the anterior intestinal portal. This region of thickened, splanchnic mesoderm is prospective cardiac mesoderm.
thickened, splanchnic mesoderm is prospective cardiac mesoderm.
through somites through somites
In this section through a pair of somites, the neural folds have not yet closed together. The somites developed from dorsal mesoderm In this section through a pair of somites, the neural folds have not yet closed together. The somites developed from dorsal mesoderm (D) and are located on each side of the neural folds and notochord. Lateral and adjacent to the somites is a small region of mesoderm (D) and are located on each side of the neural folds and notochord. Lateral and adjacent to the somites is a small region of mesoderm known as the intermediate mesoderm (I). The intermediate mesoderm will develop into the kidneys. Lateral to the intermediate known as the intermediate mesoderm (I). The intermediate mesoderm will develop into the kidneys. Lateral to the intermediate mesoderm, is the lateral plate mesoderm (L) which will delaminate to form the somatic and
mesoderm, is the lateral plate mesoderm (L) which will delaminate to form the somatic and splanchnic mesodermal layersplanchnic mesodermal layers.s.
through anterior tip of head fold through anterior tip of head fold
In this section, the anterior tip of the head fold can be seen. The portions that are visible at this level are portions of the neural folds. In this section, the anterior tip of the head fold can be seen. The portions that are visible at this level are portions of the neural folds. Recall that the neural folds form from a
Recall that the neural folds form from a thickened region of dorsal ectoderm by a thickened region of dorsal ectoderm by a process called neurulation. The neural folds will fuseprocess called neurulation. The neural folds will fuse to form the neural tube, the forerunner of the brain and
to form the neural tube, the forerunner of the brain and spinal cord. Below the neural folds, a space is evident. This space is called thespinal cord. Below the neural folds, a space is evident. This space is called the subcephalic space or pocket. Below the subcephalic space
subcephalic space or pocket. Below the subcephalic space is a region consisting of is a region consisting of a layer of ectoderm and a layer of ectoderm and a layer of endoderm. Thisa layer of endoderm. This region is called the proamnion.
region is called the proamnion.
through region of Hensen's node through region of Hensen's node
The level of sectioning has now reached Hensen's node, the cephalic end of the primitive streak. Hensen's node is the functional The level of sectioning has now reached Hensen's node, the cephalic end of the primitive streak. Hensen's node is the functional equivalent to the dorsal lip of
equivalent to the dorsal lip of the blastopore in the amphibian embryo.the blastopore in the amphibian embryo.
through primitive streak through primitive streak In the centre of the
In the centre of the photograph, note the primitive streak which consists of the photograph, note the primitive streak which consists of the primitive groove and the two primitive ridges. Note theprimitive groove and the two primitive ridges. Note the ectoderm, mesoderm, and endoderm. This photograph is the last in the series. Note that there are 35 more sections to reach THE ectoderm, mesoderm, and endoderm. This photograph is the last in the series. Note that there are 35 more sections to reach THE CAUDAL END OF THIS EMBRYO.
33 HOUR CHICK EMBRYO
33 HOUR CHICK EMBRYO
through head at level of prosencephalon and optic vesicles through head at level of prosencephalon and optic vesicles
In this more caudal section, the optic vesicles are seen as lateral bulges of the prosencephalon. The optic vesicles are the In this more caudal section, the optic vesicles are seen as lateral bulges of the prosencephalon. The optic vesicles are the forerunners of the retinal portions of the eyes. Note the close proximity of the optic vesicles to the overlying head ectoderm. forerunners of the retinal portions of the eyes. Note the close proximity of the optic vesicles to the overlying head ectoderm. The optic vesicles will i
The optic vesicles will induce this overlying ectoderm to thicken, invaginate, and nduce this overlying ectoderm to thicken, invaginate, and form the lens vesicles.form the lens vesicles.
The extraembryonic germ layers are evident below the developing head. Note that the mesoderm does not extend into the The extraembryonic germ layers are evident below the developing head. Note that the mesoderm does not extend into the region below the head fold. This region, known as the proamnion, consists of a layer of ectoderm underlain with a layer of region below the head fold. This region, known as the proamnion, consists of a layer of ectoderm underlain with a layer of endoderm. The lack of mesoderm at this stage makes this region very pale staining in whole mounts. The proamnion is a endoderm. The lack of mesoderm at this stage makes this region very pale staining in whole mounts. The proamnion is a region that will eventually
region that will eventually be overgrown and disappear.be overgrown and disappear.
through head at level of mesencephalon, notochord, foregut, and oral plate through head at level of mesencephalon, notochord, foregut, and oral plate
At this level, sectioning has now reached the notochord. The notochord is evident ventral to the mesencephalon (midbrain). At this level, sectioning has now reached the notochord. The notochord is evident ventral to the mesencephalon (midbrain). V
Ventral to the notochord, the foregut appears as entral to the notochord, the foregut appears as a smile-shaped cavity delimited by a smile-shaped cavity delimited by thin endodermally derived walls. thin endodermally derived walls. Note thatNote that the mid portion of the floor of the foregut is slightly thickened. Below this region is a region of slightly thickened ectoderm. the mid portion of the floor of the foregut is slightly thickened. Below this region is a region of slightly thickened ectoderm. This region is the oral plate which will become perforated at a later date to form the mouth. Below the head fold is the This region is the oral plate which will become perforated at a later date to form the mouth. Below the head fold is the subcephalic space and extraembryonic germ layers.
subcephalic space and extraembryonic germ layers.
through rhombencephalon, foregut, and heart through rhombencephalon, foregut, and heart
This section is posterior to the head fold. Note the absence of the subcephalic space. The portions of the embryo that will This section is posterior to the head fold. Note the absence of the subcephalic space. The portions of the embryo that will become part of the body of the embryo are continuous with the portions that will form the extraembryonic membranes. Note become part of the body of the embryo are continuous with the portions that will form the extraembryonic membranes. Note the rhombence
the rhombencephalophalon n (hind(hindbrain)brain), , notocnotochord, and hord, and foreforegut. Vegut. Ventral to ntral to the foregutthe foregut, , obserobserve ve the anterior portion of the anterior portion of thethe developing heart.
developing heart.
through rhombencephalon, foregut, and vitelline veins through rhombencephalon, foregut, and vitelline veins
Sectioning has now reached the posterior portion of the heart where the heart bifurcates into the vitelline veins. The vitelline Sectioning has now reached the posterior portion of the heart where the heart bifurcates into the vitelline veins. The vitelline veins (= omphalomesenteric veins) bring blood from the yolk sac to
veins (= omphalomesenteric veins) bring blood from the yolk sac to the posterior portion of the heart.the posterior portion of the heart.
through rhombencephalon, anterior intestinal portal, and vitelline veins through rhombencephalon, anterior intestinal portal, and vitelline veins
This section is posterior to the heart at the level of the anterior intestinal portal. Note that the endoderm of the foregut is This section is posterior to the heart at the level of the anterior intestinal portal. Note that the endoderm of the foregut is continuous with the extraembryonic endoderm. The vitelline veins are located on each
continuous with the extraembryonic endoderm. The vitelline veins are located on each side of the anterior intestinal portal.side of the anterior intestinal portal.
through spinal cord and fourth pair of somites through spinal cord and fourth pair of somites
Recall that somites are discrete blocks of tissue arising from dorsal mesoderm. The somites will develop into the vertebrae and Recall that somites are discrete blocks of tissue arising from dorsal mesoderm. The somites will develop into the vertebrae and body muscles, and will contribute cell
body muscles, and will contribute cells to the dermis of the skin.s to the dermis of the skin.
through neural folds through neural folds
Note the flat appearance of the embryo in this section. At this level, the formation of the neural tube has not been completed Note the flat appearance of the embryo in this section. At this level, the formation of the neural tube has not been completed and the neural folds are evident. Note the
and the neural folds are evident. Note the notochord and the layers of ectoderm, mesoderm, and endoderm.notochord and the layers of ectoderm, mesoderm, and endoderm.
through Hensen's node through Hensen's node
The level of sectioning has now reached Hensen's node, the cephalic (=anterior) end of the primitive streak. Hensen's node is The level of sectioning has now reached Hensen's node, the cephalic (=anterior) end of the primitive streak. Hensen's node is homologous to the dorsal lip of the bl
homologous to the dorsal lip of the blastopore in the amphibian embryo. Review the significance of astopore in the amphibian embryo. Review the significance of these structures.these structures.
through primitive streak through primitive streak
In the centre of the photograph, the primitive streak which consists of the primitive groove bordered on each side by the In the centre of the photograph, the primitive streak which consists of the primitive groove bordered on each side by the primitive ridges is visible. Note the ectoderm, mesoderm, and endoderm. This photograph is the last in the series. Sixty-two primitive ridges is visible. Note the ectoderm, mesoderm, and endoderm. This photograph is the last in the series. Sixty-two more sections were required to reach THE CAUDAL END