External: Lens vesicles are closed; nasal pits are appearing; hand plates are forming.

Internal: Foramen secundum begins to develop in the heart; a definite intestinal loop and caecum are present; lobar buds appear in the bronchial tree; the pelvis of the ureter develops, and the primary urogenital sinus forms; the future cerebral hemispheres are better delineated, the future paleostriatum and neostriatum become distinguishable, and the primordium of the epiphysis cerebri becomes recognizable; retinal pigment appears.

• Length: 7 - 9 mm
• The lens vesicle is no longer open and closure pores have disappeared.
• Olfactory placodes are beginning to submerge.
• Ventral segment of the hyoid bar shows the first indication of the primordium of the antitragus.
• Arm buds are regionally subdivided into distal hand segment and proximal segment that will form arm and shoulders.
• Leg buds show beginning evidences of regional differentiation.
• Ovulation age: 35 - 38 days

Question: The arm buds are divided into what segments?

Developmental Stages in Human Embryos by Ronan O'Rahilly and Fabiola Müller.  Published by Carnegie Institution of Washington, Publication 637. 1987. Stage 15 (PDF)

Stage 14

Stage 16 Stage 15 Internal