The placenta of the reindeer was examined from an anatomical point of view. The data obtained indicate five, in most cases seven well-developed cotyledons and caruncles, which are found in both horns of the uterus, therefore, the placenta of the reindeer should be classified as oligocotyledonous. Placenta fragments (from 5 mm thick and up to 3 cm2 in area) obtained from domestic reindeer (rangifer tarandus) were fixed in 10% buffered HistoSafe formalin, then dehydrated in an Isoprop solution with a sequential increase in concentration and poured into Histomix paraffin. The calculations were performed in IBM SPSS Statistics 26 and Microsoft Excel programs. For the first time, the ability of mesenchymal stromal cells to exhibit plasticity characteristic of the mesenchymal–epithelial transition has been established in the reindeer (rangifer tarandus). In the last stages of gestation, partial destruction of the epithelium of the amniou with the formation of vacuoles was established. Cytotrophoblast cells have the form of cubic, rounded–oval, flattened and polygonal cells with a sparse and moderate cytoplasm, often including small–droplet vacuoles, as a result of which some cells acquire an enlightened appearance, as well as with small and medium-sized nuclei. Fibroplastic cells of the caruncles of the maternal part of the placenta with moderate and pronounced intracellular voxelization, as a result of which they acquire a ring-shaped and enlightened morphology, which indicates vacuolar dystrophy of the epithelial cells of the choriotalianiosis villi. Fullness of the capillary network, moderate lymphocytic infiltration of the connective tissue of choriotalianiosis villi. In addition, polymorphic infiltration of the connective tissue of the villi and the stroma of the caruncles in the placentomas and pronounced hyperemia of the villi capillaries, as well as voxelization and enlightenment of the epithelial cells of the choriotalianiosis villi were revealed. Thus, the structural features of the placenta of the reindeer observed by us are the result of the adaptation of ruminant mammals to bearing and giving birth to cubs in the extreme climatic conditions of the territory of the Republic (Sakha) Yakutia.