1. Streeter GL. Developmental horizons in human embryos. Description of age group XI, 13 to 20 somites, and age group XII, 21 to 29 somites. Contrib Embryol. 1942;30:211–245.
2. Streeter GL. Developmental horizons in human embryos. Description of age group XIII, embryos about 4 or 5 millimeters long, and age group XIV, period of indentation of the lens vescicle. Contrib Embryol. 1945;31:27–63.
3. Streeter GL. Developmental horizons in human embryos. Description of age groups XV, XVI, XVII, and XVIII, being the third issue of a survey of the Carnegie Collection. Contrib Embryol. 1948;32:133–203.
4. Streeter GL. Developmental horizons in human embryos. Description of age groups IX, XX, XXI, XXII, and XIII, being the fifth issue of a survey of the Carnegie Collection (prepared for publication by C.H. Heuser and G.W. Corner). Contrib Embryol. 1951;34:165–196.
5. Heuser CH, Corner GW.Developmental horizons in human embryos. Description of age group X, 4-12 somites. Contrib Embryol. 1957;36:31–39.