consider using numbering system, and axioms to the effect that there is a single middle phalanx per finger in humans. This should perhaps be renamed 'intermediate phalanx', leaving the term middle phalanx open for the specific intermediate phalanx of a 3-phalanx digit

uberon

penultimate phalanx, phalanx II, medial phalanx, phalanx 2

UBERON:0004301

in some groups such as whales, there are multiple intermediate phalanges, Intermediate phalanges are bones found in the limbs of most vertebrates. In humans, they are the bones of the finger and toe which lie in the middle, between the two wrinkly joints. The thumb and big toe do not have intermediate phalanges. In most other vertebrates, they have a corresponding place in their limbs, whether they be paw, wing, hoof or fin

• proximal interphalangeal joint

• distal phalanx