Human Anatomy Part 1 - K. A. Dyubenko, A. K. Kolomiytsev, Y. B. Chaykovsky 2002

Special Part
Splanchnology, splanchnologia [the study of viscera] - Development of the digestive and respiratory systems
Development of the thymus

The Thymus develops primarily from the ventral Regions of the third pharyngeal pouch and, to a lesser extent, the fourth pouch. The thymic rudiments approach each other, fuse, and migrate in a caudal direction. Mesenchymal Cells, followed by lymphocytes whose precursors originate in the Cytology/practical/86.html">Red Bone Marrow, infiltrate the epithelial rudiments of the Thymus gland. The thymic epithelium transforms into reticuloepithelial tissue, which outwardly resembles reticular Connective Tissue. By the end of the third month, the thymic reticuloepithelium becomes populated with lymphocytes.

The Parathyroid glands develop from the dorsal PARTS OF THE third and fourth pharyngeal pouches. They appear as epithelial cords that detach from their site of origin and penetrate the superficial regions of The Thyroid Gland. In mammals, a rudimentary fifth pair of pharyngeal pouches forms from the lining of the pharyngeal gut; these pinch off to become the so-called ultimobranchial bodies (postbranchial bodies). Their cellular elements infiltrate the thyroid gland, giving rise to cells that produce the polypeptide hormone thyrocalcitonin, which acts as an antagonist to the parathyroid hormone (parathyrin).



Last update: 08/08/2026

Editorial and Educational Adaptation: This material has been compiled based on the primary/original source text. The project team performed an editorial review, corrected technical inaccuracies, structured sections, and adapted the content for an educational format.

What was processed:

  • elimination of formatting defects (OCR errors, structural breaks, corrupted characters);
  • editorial organization of content;
  • standardization of terminology in accordance with academic sources;
  • verification of factual statements against the original source text.

All mentions of the author, publication year, and origin of the primary text have been preserved in accordance with the source.