In the dissertation, the chronological sequence of the prenatal morphogenesis and the formation of thyroid and parathyroid glands, cervical parts of trachea and esophagus was investigated using adequate modern morphological research methods. It was determined that at the beginning of the 4th week of embryogenesis (embryos of 4.0-4.3 mm of the parietal-coccygeal length (PCL)) the thyroid primordium appears as an oropharynx epithelial outpouching on the midline between the 1st and 2nd pharyngeal pouches that begins to lose the connection with oropharynx in 5.5-6.0 mm embryos. Later the topographic-anatomical connections of the thyroid primordium and the 4th pharyngeal arteries, the inferior ganglion of the vagus nerves (embryos of 6.0-8.0 mm of the PCL) and the primitive aortic arch (embryos of 8.0-10.0 mm of the PCL) are formed. As a result, the thyroid primordium appears as a groove-like plate. The bilobation of the thyroid primordium starts at the end of the 6th week of embryogenesis (embryos of 11.0-13.0 mm of the PCL). The parathyroid primordia appear during the 5th week of the prenatal development (embryos of 6.0-8.0 mm of the PCL); the superior and inferior parathyroid glands develop from the epithelial outpouchings of the dorsal part of the 3rd and 4th pharyngeal pouches, respectively. The following stages of thyroid organogenesis occur during the pre-fetal period: bilobation; loss of the connection to the aortic arch and development of the close correlative relationship with the laryngeal primordium and vagus nerves which causes the thyroid gland to assume a half-ring shape (pre-fetuses of 14.0-17.0 mm of the PCL); intensive growth of the cricoid arch which results in separation of the isthmus from the lateral lobes of the thyroid gland, change of the gland’s form to H-like and fragmentation of the caudal part of thyroid-lingual cord (pre-fetuses of 18.0-24.0 mm of the PCL); beginning of the folliculogenesis in the pre-fetuses of 29.5-31.0 mm of the PCL and gradual change of the thyroid gland’s shape to the horseshoe form, and setting of the syntopical interrelations with the laryngeal cartilages, trachea, common carotid arteries and vagus nerves (pre-fetuses of 54.0-79.0 mm of the PCL). The critical periods of neck organs morphogenesis in human embryos and pre-fetuses are: the 5th week – intensive formation of thyroid and parathyroid primordia; the 6th week – formation of laryngeal cartilages primordia; the 7th week – esophageal recanalization; the 9th week – laryngeal recanalization. The considerable anatomical variability of the outer form of the thyroid and parathyroid glands in the fetal period of human ontogenesis was detected. The thyroid gland of the 4-5 months fetuses has the form of letter «Н» (45.83%) or the half-moon shape (16.66%), the fetuses at 6-7 months mostly had H-like (21.73%) and butterfly-like asymmetric (17.38%) forms, and by the end of fetal period typical shapes are: butterfly-like (symmetric – 17.86% and asymmetric – 14.29%), H-like (21.43%) and half-moon (14.29%). The rare forms of the thyroid glands are rectangular, five-parted with the shape variability of each of its parts, L-like and V-like, boat-shaped (two isolated asymmetric parts); superior parathyroid glands usually have oval (35.87%), elongated (29.35%) and rounded (17.39%) shapes; inferior parathyroid glands have rounded (42.71%) and lenticular (20.83%) forms. In 42.53% of investigated fetuses the cervical part of trachea was shifted to the right from the median sagittal plane and the cervical part of esophagus was located in the median sagittal plane. In 32.18% of observations the cervical parts of trachea and esophagus were in the median sagittal plane. In 13.8% of fetuses the cervical part of trachea was in the median sagittal plane and the cervical part of esophagus was shifted to the left. In 8.04% of fetuses the cervical part of trachea was shifted to the right and the cervical part of esophagus was shifted to the left from the median sagittal plane. In 3.45% of cases the cervical parts of trachea and esophagus were shifted to the left from the median sagittal plane. The intensive development of the cervical part of trachea goes on the 6th, 7th and 9th months of the prenatal growth and the cervical part of esophagus – in the fetuses at 5th, 7th and 10th months of development. Key words: cervical region, thyroid gland, trachea, esophagus, prenatal morphogenesis, anatomical variability, human being. Branch-Medicine.
