A Human Embryo of Carnegie Stage 13

Abstract

A human embryo obtained from a salpinx resected for the treatment of an ectopic gestation was serially sectioned and observed. Four chambers of the heart were well delineated, though not completely separated. The dorsal pancreas was observed while the ventral pancreas was not yet formed. It was hard to clearly demarcate the cecal area because of no obvious dilatation. The septum transversum was nearly completely occupied by the hepatic parenchyme. The gall bladder-cyctic duct primordium was also observed. The intestine distal to the duodenum was attached to the posterior body wall by a prominent dorsal mesentery. The respiratory tree showed primary bronchi, and no mesenchymal differentiation around the tree was achieved yet. The mesonephric system showed variable developmental features depending on their location in the body. The mesonephric duct was already connected to the cloaca, and some localized dilatation of the duct surrounded by mesenchymal condensation, which would become the metanephric blastema, foretold the formation of the ureteric bud. The otocyst had been completely separated from the skin ectoderm and the endolymphatic duct had begun to form. Eye primordium observed was the optic cup. The well established lense placode impended to invaginate. Although this embryo showed a few characteristics of stage 14, it may be reasonable to regard this embryo as an older member of stage 13, considering the overall developmental status.