ANATOMY/DENTAL STUDENT/ EMBRYONIC FOLDING

19. Somites
• Somites are bilaterally paired blocks of paraxial mesoderm that form
in the embryonic stage
• 40-44 in number
• Develop cranio caudally
• Divided into ventromedial and dorsolateral parts
• The ventromedial parts of a pair of somites fuse to form a vertebra
• The dorsolateral parts form the muscles, ligaments attached to the
vertebrae and the dermis of the skin covering the vertebrae

21. ECTODERMAL DERIVATIVES
• central nervous system (the brain and spinal cord);
• the peripheral nervous system;
• the sensory epithelia of the eye, ear, and nose;
• the epidermis and its appendages (the nails and hair);
• the mammary glands;
• the hypophysis;
• the subcutaneous glands;
• and the enamel of the teeth

22. MESODERMAL DERIVATIVES
• connective tissue,
• cartilage,
• and bone;
• striated and smooth muscles;
• the heart, blood and lymph vessels and cells;
• the kidneys; the gonads (ovaries and testes) and genital ducts;
• the serous membranes lining the body cavities;
• the spleen;
• the suprarenal (adrenal) cortices

23. ENDODERMAL DERIVATIVES
• the epithelial lining of the gastrointestinal and respiratory tracts;
• the epithelial lining of the urinary bladder and urethra;
• the pancreas
• liver
• the parenchyma of the tonsils
• the thymus,
• the thyroid,
• the parathyroids,
• the epithelial lining of the tympanic cavity, tympanic antrum, and auditory
tube