Fifty human maxillary second molars were injected with china ink, decalcified, cleared, and used in vitro study to determine the number of root canals, the frequency and location of lateral canals, canals per root, and frequency of apical deltas. The results were as follows. 1. The mesiobuccal root was found to contain a single primary canal in 62% of the teeth studied and two canals in 38% of the teeth studied. 2. In mesiobuccal roots with two canals, the seperated apical foramen appeared 24% of the specimens and the common apical foramen 14% of the specimens. 3. Of the 169 canals studied, 23.1% of the canals were found to contain lateral canals and these ramifications were mainly located in the apical third of the root.