AN ATLAS OF HUMAN EMBRYOGENESIS

Day 22
Day 32
Day 42
Day 52
Week 9
Week 30

Index

Embryogenesis
at a
glance

Germ Layer
Derivatives

Signal transmission
in utero

Amnion
enblargement

Method for
measuring
the length
of fetus

Ultrasound
of human
embryo

Pregnant
uterus,
Week 5

Pregnant
uterus,
Week 8

Transfer
across
the placental
membrane

Chorionic villus

Chorionic
villus
sampling

Delivery

Placenta

DAY	PROMINENT FEATURES	CARNEGIE STAGE	ORIENTATION	DRAWINGS	IMAGES	IMAGES
Follicular Development	Development of embryo during the first few days	-			Fertilization	Prenatal development
First two weeks	Development of embryo during the first two weeks	1-6			Development of embryo during the first two weeks
14	Lacunar networks have developed	6	Syncytiotrophoblast Uterine cavity	Blastocyst	Conceptus	Embryo at Carnegie stage 6
18	Exposed by removing the amnion	8	Oropharyngeal Cloacal	Dorsal view	Folding of the neural plate, day 18	Embryonic disc
21	1-3 somites. Flat embryonic disc. Deep neural groove and prominent neural folds. One to three pairs of somites present. Head fold evident.	9	Cranial Caudal	Dorsal view	Folding of the neural plate, day 21	Folding of cranial end, day 21
22	4-12 somites. Embryo straight or slightly curved. Neural tube forming or formed opposite somites, but widely open at rostral and caudal neuropores. First and second pairs of branchial arches visible.	10	Cranial Caudal	Dorsal view	Folding of embryo, day 22	4^th week somite, day 22
24	13-20 somites. Embryo curved owing to head and tail folds. Rostral neuropore closing. Otic placodes present. Optic vesicles formed.	11	Cranial Caudal	Dorsal view	Effect of the head fold, comparison images day 24 resp 26	4^th week somite, comparison images of day 24, 26 resp 28
26	21-29 somites. Upper limb buds appear. Rostral neuropore closed. Caudal neuropore closing. Three pairs of branchial arches visible. Heart prominence distinct. Otic pits. present.	12	Cranial Caudal	Lateral view	Folding of embryo, day 26	Folding of cranial end, day 26
28	30-35 somites. Embryo has C-shaped curve. Caudal neuropore closed. Upper limb buds are flipper-like. Four pairs of branchial arches visible. Lower limb buds appear. Otic vesicles present. Lens placodes distinct. Attenuated tail present.	13	Cranial Caudal	Lateral view	Folding of embryo Sections	Folding the caudal end, 4 ^th week
32 top	Upper limbs are paddle-shaped. Lens pits and nasal pits visible. Optic cups present.	14	Cranial Caudal	Lateral view	Digital rays + Photograph of embryos Lateral view	Craniofacial region, day 32
36	Hand plates formed; digital rays present. Lens visicles present. Nasal pits prominent. Lower limbs are paddle-shaped. Cervical sinuses visible.	15	Cranial Caudal	Lateral view	Digital rays + Photograph of embryos	Head transverse section
40	Foot plates formed. Pigment visible in retina. Auricular hillocks developing.	16	Cranial Caudal	Lateral view
42 top	Digital rays clearly visible in hand plates. Auricular hillocks outline future auricle of external ear. Trunk beginning to straighten. Cerebral vesicles prominent.	17	Cranial Caudal	Lateral view
44	Digital rays clearly visible in foot plates. Elbow region visible. Eyelids forming. Notches between the digital rays in the hands. Nipples visible.	18	Cranial Caudal	Lateral view	Digital rays, day 44
48	Limbs extend ventrally. Trunk elongating and straightening. Midgut herniation prominent.	19	Cranial Caudal	Lateral view	Digital rays, day 48
51	Upper limbs longer and bent at elbows. Fingers distinct but webbed. Notches between the digital rays in the feet. Scalp vascular plexus appears.	20	Cranial Caudal	Lateral view
52 top	Hands and feet approach each other. Fingers are free and longer. Toes distinct but webbed. Stubby tail present.	21	Cranial Caudal	Lateral view
54	Toes free and longer. Eyelids and auricles of external ears more developed.	22	Cranial Caudal	Lateral view
56	Head more rounded and show huamn characteristics. External genitalia still have sexless appearance. Distinct bulge still present in umbilical cord, caused by herniation of intestines. Tail has dissappeared.	23	Cranial Caudal	Lateral view	Digital rays + Photograph of embryos
WEEK top	PROMINENT FEATURES	DAY/MONTH	ORIENTATION	VIEW SORT	IMAGES	IMAGES
9	Growth in body length accelerates rapidly	63/2	Cranial Caudal	Lateral view	Size of fetus, week 9
12	Mature fetal form is established	84/3	Cranial Caudal	Lateral view	Size of fetus, week 12
20	Fetus covered with fine downy hair called lanugo	140/5	Cranial Caudal	Lateral view	Size of fetus, week 20
30 top	The pupillary light reflex of the eyes can be elicited	210/7.5	Cranial Caudal	Lateral view	Size of fetus, week 30
38	Chest is prominent and the breasts protrude slightly in both sexes	266/9.5	Cranial Caudal	Lateral view	Size of fetus, week 38