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Early chick embryo

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Whole Mount of Chick Blastoderm

AO = area opaca, AP= area pellucida

P= region of thick

blastoderm thatmarks the futureposterior region of theembryo; area wheregastrulation begins

Arrows= movementof rapidly dividingcells of epiblast layer

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Chick Embryo - Primitive Streak Stage

The primitive streakisthe region where epiblastcells converge (solidarrows) and movethrough a groove into the

blastocoel (dashedarrows). The primitivesteak consists of a lightlystaining groove borderedon each side by darker

staining ridges. Hensen'snode marks the anteriorof the streak and P marksthe posterior.

AO= area opaca,

AP = area pellucida,P= posterior

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Cross sections through Primitive streak

Key to Upper Crosssection:

AO = area opaca

AP= area pellucida

^^= remnants of yolkgranules,

arrows = direction ofingression of embryonic

cells Lower Cross Section

shows the three germlayers formed by theprocess of gastrulation.

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24-hr chick embryo

AIP = anterior

intestinal portal

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Prominent neurocoele (neurocoel)in the

Portions of the notochord arevisible just ventral to the brain andspinal cord.

Foregut (asterisk) is seen as a

cavity extending from the top ofthe head to the anterior intestinalportal.

Between the foregut andsubcephalic pocket is a region ofsplanchnic mesoderm that willform the heart.

Somites are not visible in thissection (the plane of section isbetween the paired rows ofsomites).

A Sagittal Section of a 26 Hour Chick

Embryo

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The 33 Hour Chick Embryo - Whole Mount

AIP = anteriorintestinal portal

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Sagittal Section of a 33 Hour Chick

Embryo

divisions of thedeveloping brain.

neuromeres in therhombencephalon.

Neuromeres aresegmental divisions of thebrain seen in the embryo.

heart forming region isnow seen much moreclearly

portions of the somitesare seen

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Chick embryo 33 hrs serial cross

section

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48 Hour Chick Embryo

Whole Mount

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Details of Head

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48 Hour Chick Embryo

The brain now consists of five parts or"vesicles". The prosencephalon hasdivided into two regions, the telencephalon

and the diencephalon. The region of themesencephalon remains as a single unitand retains its name of mesencephalon.The rhombencephalon has become the

metencephalon and the myelencephalon.Each of these embryonic parts of the brainwill form distinct parts of the adult brain.

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Details of Pharynx

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Details of Heart

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48 Hour Chick

Embryo serial cs

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72 Ho r Chick Embr o

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72 Hour Chick Embryo

Whole Mount

1 = Telencephalon

2 = Diencephalon

3 = Mesencephalon4 = Metencephalon

5 = Myelencephalon

* = Otic capsule

^ = Olfactory pit