placodes, lens pit, otocyst, nasal pits moved ventrally, fourth ventricle of brain Mesoderm: heart prominence, ossification continues Head: forebrain, eye, external acoustic meatus hearing - otic capsule connected with the basal plate and with the future exoccipitals. Tip of the cochlea is elongated and curled. Tensor tympani and stapedius present. Stage 21: c. 51days Ectoderm: sensory placodes, nasal pits moved ventrally, fourth ventricle of brain Mesoderm: heart prominence, ossification continues Head: nose, eye, external acoustic meatus Body: straightening of trunk, heart, liver, umbilical cord Limb: upper limbs longer and bent at elbow, foot plate with digital rays begin to separate, wrist, hand plate with webbed digits Stage 22: c. 53 days Mesoderm: heart prominence, ossification continues Head: nose, eye, external acoustic meatus Body: straightening of trunk, heart, liver, umbilical cord Limb: upper limbs longer and bent at elbow, foot plate with webbed digits, wrist, hand plate with separated digits Stage 23: c. 56 days final embryonic stage, after this development is described as "fetal" through the entire second and third trimester. Mesoderm: ossification continues Head: eyelids, external ears, rounded head Body: straightening of trunk, intestines herniated at umbilicus Limbs: hands and feet turned inward See also Mammalian embryogenesis External links UNSW Embryology - Carnegie Stages Overview at umich.edu Details on stages at lsuhsc.edu List of structures by week, at mrc.ac.uk Diagrams at actual size at Visible Embryo Virtual human embryo detailing stages References Hill, M.A. (2016) Embryology Carnegie Stages. Retrieved August 19, 2016, from https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_Stages Embryology