Occasionally accessory bones are found in the carpus, but of more than 20 such described bones, only four (the central, styloid, secondary trapezoid, and secondary pisiform bones) are considered to be proven accessory bones. Sometimes the scaphoid, triquetrum, and pisiform bones are divided into two.
perforce definition: by or through necessity; necessarilyOrigin of perforceMiddle English par force from OFr: see per and force...
A membrane is a thin layer that may or may not allow particles to pass through it. Permeable is defined as a membrane that can be crossed by particles, ions, or water.