Manava Dharmashastra 2.90

2.90

śrotrādīni prasiddhāni | adhiṣṭhānabhedāccakṣuṣī iti dvivacanam | anyatra tadādhārāyāḥ śakterekatvādekavacanam | upasthaḥ śuknotsarjanaḥ puṃso rajastadādhāraśca striyāḥ |
dvandvanirdiṣṭayoḥ ‘prāṇyaṅgatvādekavadbhāvaḥ’ (pā. sū. 24|12) | vāk tālvādiḥ śabdābhivyañjakaḥ śarīrāvayavanāmanirdeśo'yam |

Medhātithi’s commentary (manubhāṣya):
The Ear and the rest are well known. We have ‘Eyes’ in the Dual, in view of the two different substrata (of the Visual Organ); in other places we have the singular number in view of the fact that the Faculty itself, subsisting in the said substrata, is one only.