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Preimplantation
The 1st week when fertilization and implantation occur. -
Period: to
9 Months
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2nd Week
During the second week, the blastocyst grows by proliferation. Differentiation also occurs. During this week the placenta also develops. -
3rd Week
During this week the Mesoderm, Endoderm, and Ectoderm are developed. The primitive streak forms and allows symmetry on both the right and left halves. The cephalic end forms the head end of the disk. The caudal end forms the tail end of the disk. During the end of the third week the central nervous system begins to develop. -
4th Week
Embryonic folding occurs during this week. The digestive tract is starting to form and is separated into three parts: foregut, midgut, and hindgut. Cervical development begins in the 4th week and ends in the fetal period. Also during this week the face and neck start to develop.
-Mandibular processes
-Mandibular arch
-Frontonasal process forms eventually forming nasal pits -
5th Week
During the 5th week the intermaxillary segment forms. From the 5th to the 12th week the nasal cavity and septum develop. From the 4th to the 12th week the tongue develops. -
6th Week
During the 6th week, the two palatal shelves fuse together forming the secondary palate. The upper and lower lip develop during this week and this is when a cleft lip can develop. -
12th Week
During the 12th week, there is palate completion. -
Fetal Period
The fetal period begins during the 9th week and continues during the remainder of the pregnancy. The embryo enlarges during this time and becomes a fetus. Fetal heartbeat and movements begin to occur at 16 weeks.