The interior was designed with two rooms for exhibition. The East Library features triple-tiered bookcases, the upper tiers of which could only be accessed by balconies. On the east wall of the East Library is a fireplace with a tapestry showing the "Triumph of Avarice". Mowbray designed eighteen lunettes and spandrels atop each wall. The figures in the lunettes alternate between allegorical female muses and notable artists, explorers, or teachers. Zodiac symbols are placed on the spandrels, as the signs of the zodiac were particularly important to J. P. Morgan. Particularly prominent are the zodiac signs over the entrance: Aries corresponds to J. P. Morgan's birth on April 17, 1837, and Gemini corresponds to his marriage to Frances Louisa Tracy on May 31, 1865. Two additional spandrels contain allegorical motifs that depict changing seasons.