UNSW Embryology Early Human Carnegie Stages	Embryology Homepage
Stages Homepage Species Stage Comparisons Stage Sequence Embryo Growth Movie Back to Human Homepage

Stage	Days (approx)	Size (mm)	Images (not to scale, click image to see original)	Somite Number	Events
1	1 (week 1)	0.1-0.15			fertilized oocyte
2	2 - 3	0.1-0.2			inner and outer cell mass
3	4 - 5	0.1-0.2			free blastocyst
4	5 - 6	0.1-0.2			attaching blastocyst
5	7 - 12 (week 2)	0.1-0.2			implantation
6	13 - 15	0.2			extraembryonic mesoderm, primitive streak
7	15 - 17 (week 3)	0.4			gastrulation, notochordal process
8	17 - 19	1.0 - 1.5			primitive pit, notochordal canal
9	19 - 21	1.5 - 2.5		1 - 3	neural folds, cardiac primordium, head fold
10	22 - 23 (week 4)	2 - 3.5		4 - 12	neural fold fuses
11	23 - 26	2.5 - 4.5		13 - 20	rostral neuropore closes
12	26 - 30	3 - 5		21 - 29	caudal neuropore closes
13	28 - 32 (week 4)	4 - 6		30	leg buds, lens placode
14	31 - 35	5 - 7			lens pit, optic cup
15	35 - 38	7 - 9			lens vesicle, nasal pit, hand plate
16	37 - 42 (week 6)	8 - 11			nasal pits moved ventrally, auricular hillocks, foot plate
17	42 - 44	11 - 14			finger rays
18	44 - 48 (week 7)	13 - 17			ossification commences
19	48 - 51	16 - 18			straightening of trunk
20	51 - 53 (week 8)	18 - 22			upper limbs longer and bent at elbow
21	53 - 54	22 - 24			hands and feet turned inward
22	54 - 56	23 - 28			eyelids, external ears
23	56 - 60	27 - 31			rounded head, body and limbs	Approximate stage of human serial series in Embryology Program

[Source: Rothenburger and Gay, 1995. and others]