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.
Developmental Stages in Human Embryos by Ronan O'Rahilly and Fabiola Müller.
Published by Carnegie Institution of Washington, Publication 637. 1987.
Stage 15 (PDF 935 KB)
QUESTION: The arm buds are divided into what segments?