protocone

from The Century Dictionary.

• noun The anterior inner cusp in an upper molar, and the anterior outer cusp in an upper premolar, of many mammals, homologous to the single cusp assumed by the tritubercular theory of dental complication to be the primitive reptilian ancestral type from which by progressive complication the teeth of mammalians have been derived. The antero-external cusp in the lower molars and premolars has similar homologies, according to the tritubercular theory, and is termed, for distinction from the upper series, the protoconid.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy A cusp in the corner of an upper molar tooth in mammals