Final answer:
The accessory bone at the 5th metatarsal is often known as an os peroneum or an os vesalianum. However, a commonly discussed condition in this area, a Jones fracture, is actually a type of fracture and not an accessory bone.
Step-by-step explanation:
The accessory bone at the 5th metatarsal of the foot is often called an os peroneum or an os vesalianum. This accessory ossicle is usually located within the peroneus longus tendon as it runs under the foot's lateral side. However, the more common variation referred to when discussing injury or pain associated at the base of the fifth metatarsal is known as a Jones fracture, which is not an accessory bone but rather a fracture of the proximal diaphysis that can sometimes be confused with an accessory ossicle.
The 5th metatarsal bone is noteworthy because its base has a large, lateral expansion providing for muscle attachments, and this area is particularly prone to injury. The metatarsal bones, of which the 5th metatarsal is one, form the anterior half of the foot, articulating posteriorly with the tarsal bones and anteriorly with the phalanges of the toes.