The notochord or chorda dorsalis ends just behind this ventral vesicle. The infundibulum (= derived from the diencephalon) appears as a half circular structure at the ventral side of the caudal part of the forebrain. The sinus rhomboidalis (diamond-shaped) is still present as the only opening of the neural tube and the primitive streak is only rudimentary. The forebrain vesicle or prosencephalon will divide, the midbrain vesicle or mesencephalon remains undivided while the hindbrain vesicle or rhombencephalon will form a series of smaller neuromeres.
At this stage 12 to 13 somites are formed.
The cranial flexure will be visible a few hours later. This region is called the proamnion.Īt about 33 hours after fertilization, the embryo is about 4 mm long and the first flexion of the originally straight embryo starts in the head region. Below the subcephalic space is a region consisting of a layer of ectoderm and a layer of endoderm. This space is called the subcephalic space or pocket. Chick Embryo 48 Hour Serial Frontal Section Prepared Microscope Slide Triarch Incorporated Aves 48 hr chick (24-28 somites) serial frontal section. Lower Cross Section shows the three germ layers formed by the process of. Below the neural folds, a space is evident.Ĭhick Embryo - Primitive Streak Stage. The neural folds will fuse to form the neural tube, the forerunner of the brain and spinal cord. Recall that the neural folds form from a thickened region of dorsal ectoderm by a process called neurulation. 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.
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