A back vowel is a sound where the back of the tongue approaches the palate.

Back vowels are vowels that are pronounced using the back of the tongue.

A central vowel is a vowel that is pronounced in the central part of the tongue.

The central vowels in Japanese are 'a', 'e', 'o'.

Front vowels are pronounced using the front part of the tongue.

A front vowel is a vowel that is articulated with the front part of the tongue.

He is doing exercises to strengthen his genioglossus muscle.

The hyoid muscle is an important muscle that connects the larynx and the tongue.

I owe him a great obligation.

The greenhouse effect is causing the earth's temperature to rise.