At 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. The cranial flexure will be visible a few hours later. At this stage 12 to 13 somites are formed.

Whole-mount preparation 72 hours after fertilization; Information: 72 Hours after fertilization, the rotation of the embryo to the left is arrived such behind the region of the heart and only the caudal part of the embryo must twist 90 degrees.

The eye vesicles are rather large. 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. The sinus rhomboidalis (diamond-shaped) is still present as the only opening of the neural tube and the primitive streak is only rudimentary.

Budova avtomata ak 47. The infundibulum (= derived from the diencephalon) appears as a half circular structure at the ventral side of the caudal part of the forebrain. The notochord or chorda dorsalis ends just behind this ventral vesicle. Later on, 36 hours after fertilization, the heart, which has a bilateral origin in the mesodermal layer, is a S-shaped tube which protrudes to the right of the embryo (in upper view).

Outside, in the area vasculosa (= forseen of blood vessels) the formation of blood islands continues. The primitive streak can only still be discerned below the sinus rhomboidalis. Early embryonic developmental features that are shown on this page: • Whole mount preparation 33 hours () • Whole mount preparation 36 hours () • Cross sections 36 hrs; formation of eye, heart and intestines ( ) Stage 33 hours Information: At 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 and the cranial flexure will be visible a few hours later. At this stage 12 to 13 somites are formed. The eye vesicles are rather large. 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. The sinus rhomboidalis (diamond-shaped???) is still present as the only opening of the neural tube and the primitive streak is only rudimentary.

The infundibulum (= derived from the diencephalon) appears as a half circular structure at the ventral side of caudal part of the forebrain. The notochord or chorda dorsalis ends just behind this venral vesicle.

Embryology of chicken 33 hours after fertilization: stained whole mout preparation 1 = Proamnion, 2 = Prosencephalon, 3 = Mesencephalon, 4 = Rhombencephalon, 5 = Somite, 6 = Eye vesicle, 7 = Foregut, 8 = Chorda (translucent), 9 = Heart, 10 = Lateral mesoderm, 11 = Spine, 12 = Sinus rhomboidalis, 13 = Primitive streakp, 14 = Blood islands Dorsalview and longitudinalsection at 33 hrs according to Patten Patten, B.M. The Early Embryology of the Chick. Philadelphia: P. Blakiston's Son and Co.