C

Reasoning: The four dorsal interosseous muscles are numbered from radial to ulnar. The 2nd and 3rd dorsal interossei both insert into the radial and ulnar sides of the middle finger, giving it two separate dorsal interosseous attachments; the index and ring fingers receive only one each, and the little finger has none because it already has its own abductor digiti minimi [von Schroeder & Botte 2001, PMID 11210974; Nayak et al. 2016, PMID 27504270].