A 68-year-old woman from Mumbai presents with progressive weakness and atrophy of the intrinsic muscles of her right hand over the past 3 months. She reports numbness and tingling in the medial 1.5 fingers (ring and little fingers) and the medial aspect of the palm. On examination, there is marked wasting of the hypothenar eminence and interossei. Grip strength is severely reduced. What is the most likely nerve root and dermatome involved?