1. Arey L. B.(1937) “Developmental Anatomy” 3rd Edition:142.
2. Section of Dermatology
3. Boyd W.(1947) “Textbook of Pathology” 5th Edition:307.
4. Clark W. E. Le Gros(1946) “Tissues of the Body” 2nd Edition:276.
5. Cunningham D. J.(1947) “Textbook of Anatomy” 8th Edition:406.