Embryogenesis

PLEASE note that the black-and-white photographs shown here were assembled by the Carnegie Embryology Institute over several decades, beginning in 1914, as part of a national effort to identify, describe, and standardize the stages of human embryological and fetal development. The photographs are of embryos that were the result of spontaneous miscarriages or that were discovered during a necessary hysterectomy. In other words, these are not photographs of intentionally-aborted embryos.



WEEK 3



STAGE 11; 23 - 26 Days; 2.5 - 4.5 mm;; Somite Number 13 - 20; rostral neuropore closes; Carnegie Stage 11; Features: rostral neuropore closing, forebrain, neural tube in region of developing spinal cord, somites, caudal neuropore, connecting stalk, amnion



WEEK 4



STAGE 12; 26 - 30 Days; 3 - 5 mm;; Somite Number 21 - 29; caudal neuropore closes; Features: day 26, 27 somites, forebrain, site of lens placode, site of otic placode , stomodeum, 1st pharyngeal arch, 2nd pharyngeal arch, 3rdpharyngeal arch, heart prominence, somite



WEEK 5



STAGE 13; 28 - 32 Days; (week 5); 4 - 6 mm;; Somite Number 30; leg buds, lens placode, pharyngeal arches; Features: site of midbrain, lens placode, site of nasal placode, 1,2,3 pharyngeal arches, L. ventricular prominence of heart, L. atrial prominence of heart, umbilical cord, lower limb bud, mesonephric prominence, upper limb bud;
STAGE 14; 31 - 35 Days; 5 - 7 mm;; lens pit, optic cup; Day 32 Features: midbrain, nasal placode, lens pit, 1,2,3 pharyngeal arches, fourth ventricle of brain, 1st pharyngeal groove, heart prominence, cervical sinus, upper limb bud, mesonephric ridge, lower limb bud, umbilical cord
STAGE 15; 35 - 38 Days; 7 - 9 mm;; lens vesicle, nasal pit, hand plate



WEEK 6



STAGE 16; 37 - 42 Days; (week 6); 8 - 11 mm; nasal pits moved ventrally, auricular hillocks, foot plate; (day 40); Features: eye showing retinal pigment, nasolacrimal groove, nasal pit, fourth ventricle of brain, umbilical cord, 1st and 2nd pharyngeal arches, cervical sinus, heart, developing arm with hand plate, foot plate
STAGE 17; 42 - 44 Days; 11 - 14 mm;; finger rays; day 42); Features: pigmented eye, nasal pit, nasolacrimal groove, external acoustic meatus, auricular hillock, heart, digital rays, liver pronminance, thigh, ankle, foot plate, umbilical cord



WEEK 7



STAGE 18; 44 - 48 Days; (WEEK 7); 13 - 17 mm;; ossification commences
STAGE 19; 48 - 51 Days; 16 - 18 mm;; straightening of trunk; day 48) Features: eyelid, eye, external acoustic meatus, auricle of external ear, digital ray, wrist, liver prominence
STAGE 20; 51 - 53 Days; (week 8); 18 - 22 mm; upper limbs longer and bent at elbow day 51); Features: scalp vascular plexus, eylid, eye, nose, external acoustic meatus, auricle of external ear, arm, elbow, wrist, liver prominence, digital rays
STAGE 21; 53 - 54 Days; 22 - 24 mm; hands and feet turned inward; day 52); Features: scalp vascular plexus, eylid, eye, nose, auricle of external ear, arm, elbow, wrist, knee, notch between digital rays, umbilical cord;



WEEK 8



STAGE 22; 54 - 56 Days; 23 - 28 mm;; eyelids, external ears
STAGE 23; 56 - 60 Days; 27 - 31 mm;; rounded head, body and limbs; Features: scalp vascular plexus, eylid, eye, nose, auricle of external ear, mouth, sholder, arm, elbow, wrist, toes separated, sole of foot, umbilical cord