1. A Site of midbrain 1st, 2nd, 3rd, and 4th pharyngeal (branchial) arches Left atrial prominence of heart Upper limb bud Somites Actual size 4.5 mm Mesonephric prominence Site of lens placode Umbilical cord Tail Lower limb bud Site of nasal placode Left ventricular prominence of heart

2. 1st pharyngeal groove (cleft) B Fourth ventricle of brain Midbrain Cervical sinus Heart prominence Upper limb bud Mesonephric ridge Somites Actual size 4.0 mm 1st, 2nd, and 3rd pharyngeal (branchial) arches Lens pit Nasal placode Umbilical cord Tail Lower limb bud

3. Week 5 32 days Flipperlike upper limb bud

4. Week 5 35 days Hand plate formed

5. Week 6 44 days Digital rays appear in hand plate Digital ray Notch between digital rays

6. Week 7 48 days Upper limbs bend at elbow; fingers are short and webbed

7. Week 8 56 days Fingers and toes are distinct and separated

8. A B

9. C D

10. A B

11. A C D B Loose mesenchyme Condensed mesenchyme Ectoderm Mesenchymal primordia of forearm bones Apical ectodermal ridge Carpal bone Carpus Radius Scapula Humerus Ulna Metacarpals Phalanges Cartilage Ectoderm Humerus

25. Progress zone??