Shiva Purana
नकारश्शिर उच्येत मकारस्तु शिखोच्यते ॥ शिकारः कवचं तद्वद्वकारो नेत्रमुच्यते ॥ ५२ ॥
The syllable n is called the head, and the syllable m is called the head. The hunter is the shield and the vowel is the eye.
english translation
nakArazzira ucyeta makArastu zikhocyate ॥ zikAraH kavacaM tadvadvakAro netramucyate ॥ 52 ॥
hk transliteration by Sanscript