What term describes the part that runs straight from the cuticle down the side of the nail to the end of the extension?

The correct term that describes the part running straight from the cuticle down the side of the nail to the end of the extension is the sidewall. The sidewall is the area on either lateral side of the nail plate and plays a crucial role in the structure and aesthetic of the nail. It helps to define the shape and support the nail, and is an important consideration during nail care and extensions, as improper treatment of the sidewalls can lead to lifting or damage to the nail enhancements.

The apex refers to the highest point of the nail arch, contributing to the strength and contour of the nail, but it does not run from the cuticle down the side. The free edge is the part of the nail that extends past the fingertip; it is not connected to the cuticle nor runs down the side. The base refers to the area where the nail meets the skin at the proximal nail fold, which is different from the side structure. Understanding these distinctions helps in accurately describing and caring for the nail structure.