Placentation in rodents (Glires). (A) Hemotrichorial placenta of the lemming, Lemmus lemmus. One layer of cellular trophoblast (T1) and two layers of syncytiotrophoblast (T2–T3) are interposed between the maternal blood space (MBS) and fetal capillaries (FC). (B) Hemomonochorial placenta of the golden-mantled ground squirrel, Spermophilus lateralis. The syncytiotrophoblast (SYN TR) has intrasyncytial bays (ISL). (C) Hemomonochorial placenta of a jumping mouse, Zapus sp. The interhemal membrane includes a single layer of giant trophoblast cells (CYTO TR). (D) Endotheliochorial placenta of a kangaroo rat, Dipodomys sp. The interhemal membrane comprises the endothelium of the maternal capillary (MC), cellular trophoblast (CYTO TR) with lipid inclusions and the endothelium of the fetal capillary (FC).