The secretory cells of the mammary gland are very diverse in their size, shape, and structure. These are highly specialized cells adapted to the synthesis, accumulation, storage, and excretion of milk. The main feature of glandular cells is the presence of secreted substances. Electron microscopy shows that substances of different secretory cells types have various electron densities. Occasionally, two or more types of secretory granules differing in size and composition can be found in one cell. The material for the morphological study was small (2‐4 mm) tissue samples of goat lactating mammary glands. Pieces were taken from deeper areas of the breast parenchyma. Ultrathin sections with a 50‐70 nm thickness were obtained for electron microscopic analysis using Leica UC7 ultramicrotome. Electron microscopy was performed using a JEOL JEM 1011 microscope. Micrographs were obtained using a Morada camera (Digital Imaging Solutions Inc.). The secretion of the mammary gland occurs according to the apocrine type. Picture of the lactocytes' cytoplasm apical part separation into the lumen of the alveoli is often observed on semi‐thin sections. Thus, numerous droplets of material secreted by lactocytes are found in the lumen of the alveoli. The shape of lactocytes in the lactating mammary gland is close to cubic. The height of the epithelial layer, generally, is 10‐12 microns (µm). The milk ducts, like the alveoli, are dilated. Most of them contain a significant amount of osmiophilic material secreted by the cells of the mammary alveoli. The cells of the epithelium of the single‐layered ducts have a flattened or cuboidal shape. The diameter of the ducts varies noticeably depending on location in the gland parenchyma. The intralobular milk ducts are 10‐20 µm in diameter. At the same time, the larger interlobular ducts reach a diameter of 40‐50 microns and are located in groups in the connective tissue stroma of the mammary gland. Notably, an increase in the mammary alveoli mass in the lactating gland is associated with a decrease in connective tissue volume and the almost complete disappearance of fat cells groups from it. The milk ducts of the teat zone in the lactating gland are strongly expanded, round, or slightly oval‐shaped in cross‐section with a diameter of 30‐60 microns. In contrast to the deeper zones of the mammary gland, we were unable to detect secreted substances in the dilated milk ducts near the teat area. The milk ducts we studied are located close to the most terminal sections of the mammary gland excretory system (gland cistern and teat canal). The milk is inevitably washed out from the ducts during chemical fixation and subsequent stages of objects preparation for histological analysis.

The ductus venosus is a physiological vascular shunt to the umbilical and caudal vena cava in the fetus. The umbilical vein (vena umbilicalis) leaves the placenta, enters the fetus through the foramen umbilical, and goes to the liver hilum. It carries oxygenated and nutrient‐rich blood from the placenta to the fetus. Part of the blood enters the liver through the umbilical vein, through the shunt ‐ the ductus vein enters the central venous line ‐ the caudal vena cava. This mechanism of blood redistribution is necessary for feeding the fetal brain with blood that is more saturated with oxygen. Given the scarce data on the topography, shape, and morphometric parameters of the venous duct in animals, we set the goal of revealing the methods used for its postmortem study. For a complete and comprehensive study of the topography of the venous duct, it is necessary to use a set of anatomical methods: thin anatomical preparation, vasoradiography, production of corrosive preparations, and morphometry. When conducting vasoradiography, a mass for injection prepared according to the recipe was used as a radio‐opaque mass: 45% ‐ lead white, 45% ‐ gum turpentine, 10% ‐ medical gypsum powder (M.V. Shchipakina, A.V. Prusakova, D.S. Bylinskaya, S.A. Kuga, 2013). In the manufacture of corrosive preparations, self‐hardening dental plastic was used. It belongs to the acrylic group of cold curing plastics and consists of powder and solvent components. In both cases, the injection of these substances was carried out through the umbilical vein, without opening the abdominal cavity, by accessing through the umbilical cord. After introducing the X‐ray contrast mass, the objects of study were placed in a fixing solution (10% formalin solution) and left in it for up to 5 days. Subsequently, thin anatomical preparation and photography, as well as radiography, were performed. After introducing a plastic solution, the objects were placed in chambers with a temperature of +4°C for two days. Subsequently, corrosion treatment was carried out in an aqueous potassium hydroxide solution for 4 ‐ 5 days. The morphometry of the venous duct in the study of vaso‐radiographs was carried out in the RadiAnt computer program, in the study of a corrosive preparation ‐ using an electronic caliper (Stainless hardened). On vaso‐radiographs, the ductus venous is identified as a sizeable cone‐shaped vessel located in the area of the liver hilum. The ductus venosus is identified as a craniodorsal blood vessel that flows into the caudal vena cava on the casts of the vascular bed. The proposed methods for studying the ductus venosus make it possible to accurately anatomically describe the position, shape, and size of the ductus venosus in fetuses.