1. Gray, G. W. and Wise, C. M. 1934.The Bases of Speech, 357Harpers.
2. A speech mechanism hypothesis
3. Guyer, M. F. 1937.Animal Biology, Revised Ed., 347Harpers.
4. Howell, W. H. 1933.A Text Book of Physiology, 426W. B. Sauuders Co.
5. Robinson, Arthur. 1927.Cunningham's Manual of Practical Anatomy, 8th Ed., Vol. 2, 244–49. William Wood and Co.