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G6: Fusion of mandibular arches, second and third arches. Hypopharyngeal eminence. Aortic sac. Truncus arteriosus. Pharynx, initially compressed dorsoventrally then more caudally, compressed mediolaterally in region of dense mass of mesenchyme (cf B6). Narrow oesophagus. Tracheal bifurcation dorsal to sinus venosus. Attachment of pulmonary mesenchyme to septum transversum.
DEVELOPMENT OF THE GUT
G6: Liver. Gall bladder. Cranial limb of midgut loop in mesentery with intervitelline anastomoses. Caudal attachment of mesentery with hindgut inside. Communication of intra- and extra-embryonic coeloms.
DEVELOPMENT OF THE MUSCULOSKELETAL SYSTEM
G6: Cervical region (neural tube cut very obliquely): note the wavy notochord and thin roof and floor plates. Thoracic region: alternating light and dark parts of the sclerotomes (vertebral bodies and I.V. Discs, respectively). Lumbar region: tiny, dorsal segmental branches of dorsal aorta Each little branch is aligned almost parallel to the cranial border of the next caudal dorsal root ganglion (segmented dark masses). Sacral region: oblique section of neural tube, notochord.
