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| median and horizontal plane folding resulting from growth of embryo in brain and spinal cord. side growth slower than than long axis causing folding. |
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| folding ventrally produces head and tail folds that result in cranial and caudal regions move ventrally as the embryo elongates cranially and caudally. |
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| beginning fourth week the neural fold thicken to form primordium of brain. initially projects dorsally into amniotic cavity. |
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| during longitudinal folding, part of the endoderm of the yolk sac is incorporated into the embryo as the foregut. between brain and heart. |
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| results primarily from growth of the distal part of the neural tube, the primordium of the spinal cord. |
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| part of the endodermal germ layer is incorporated into the embryo as the hindgut(primordium of the descending colon). |
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| terminal part of the hindgut dilates forming this. Primordium of the urinary bladder and rectum. |
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| primordium of the umbilical cord becomes attached to ventral surface of embryo at tail fold event |
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Definition
| diverticulum of the yolk sac becomes partially incorporated into the embryo during the tail fold. |
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Definition
| as abdominal walls form during tail fold the endoderm germ layer is incorporated into the embryo as the midgut. |
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Definition
| major changes in body form occur during the fourth week. by 24th day pharyngial arches are visible and first arch gives rise to mandibule. Upper limb buds become recognizable by day 26/27.otic pits, lens placods, ectodermal thickenings. |
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Definition
| enlargement of the head is caused mainly by the rapid development of brain and facial prominences. hyoid pharyngeal arch, upper limb buds, lower limb buds, mesonephric ridges indicate site of mesonephric kidney. |
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Term
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Definition
| upper limb begin to show regional differentiation as elbows and large hand plates develop. digital rays. auricular hillocks (future external acoustic meatus.) |
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Definition
| notches between digital rays. intestines enter exrraembryonic coelom in proximal part. |
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Definition
| scalp vascular plexus appear and form characteristic band around head. all regions of limbs apparent. ossification begins in lower limb. neck region established eyelids more obvious. |
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