SB 10.12.22

āstṛtāyāma-mārgo ’yaṁ
 rasanāṁ pratigarjati
eṣāṁ antar-gataṁ dhvāntam
 etad apy antar-ānanam
Synonyms: 
āstṛta-āyāma — the length and breadth; mārgaḥ ayam — a broad way; rasanām — the tongue; pratigarjati — resembles; eṣām antaḥ-gatam — on the inside of the mountains; dhvāntam — darkness; etat — this; api — indeed; antaḥ-ānanam — the inside of the mouth.
Translation: 
In length and breadth the animal’s tongue resembles a broad traffic-way, and the inside of its mouth is very, very dark, like a cave in a mountain.