Shatapatha Brahmana 11.4.1.5

11.4.1.5

sa vai gautamasya putra vṛto janaṃ dhāvayet yastaddarśapūrṇamāsayorvidyādyasmādimāḥ prajā adantakā jāyante yasmādāsāṃ jāyante yasmādāsām prabhidyante yasmādāsāṃ saṃstiṣṭhante yasmādāsām punaruttame vayasi sarva eva prabhidyante yasmādadhara evāgre jāyante'thottare yasmādaṇīyāṃsa evādhare prathīyāṃsa uttare yasmāddaṃṣṭrā varṣīyāṃso yasmātsamā eva jambhyāḥ

'He alone, O son of Gautama, may drive about amongst people as chosen (priest), who knows from the Full and New-moon sacrifices whereby it is that creatures here are born toothless, whereby they (the teeth) grow with them, whereby they decay with them, whereby they come to remain permanently with them; whereby, in the last stage of life, they all decay again with them; whereby the lower ones grow first, then the upper ones; whereby the lower ones are smaller, and the upper ones broader; whereby the incisors are larger, and whereby the molars are of equal size.