The phalanges or finger bones are fourteen in number; three for each finger, and two for the thumb. They are named numerically in order from the proximal towards the distal ends of the fingers i.e. the most proximal is the first phalanx and the most distal is the third phalanx.
The first phalanx (Phalanx Prima):
The first phalanx is the longest and stoutest of the three. It has a semi-cylindrical body which is curved slightly forwards. The anterior surface is flat and bounded on either side by two sharp borders to which the fibrous sheath of the flexor tendons is attached. The posterior surface is convex from side to side and is overlain by the extensor tendons. The proximal end, considerably enlarged, has a simple oval concave surface, which rests on the head of its corresponding metacarpal bone.
The second phalanx (Phalanx Secunda):
The second phalanx resembles the first in general form, but is of smaller size. It differs, however, in the form of its proximal articular surface, which is not a simple oval concavity, but is an oval area divided into two small, nearly circular concavities by a central ridge passing from anterior to posterior edge. These concavities articulate with the condylar surfaces of the proximal phalanx.
The third phalanx (Phalanx Tertia):
The third or terminal phalanx is the smallest of the three. It is easily recognized by the spatula-shaped surface on its distal extremity which supports the nail. The articular surface on its proximal end resembles that on the proximal end of the second phalanx, but is smaller.
Phalanges of thumb:
The phalanges of the thumb resemble in the arrangement of their parts to the first and third phalanges of the fingers.
Ossification of Phalanges:
The phalanges are ossified from primary and secondary centers. The primary center appears as early as the ninth week of fetal life, and the body and distal ends are developed from it. The secondary center begins to appear at about the third year and forms the proximal epiphyses which later unites with the body.