The first digit is the thumb, followed by index finger, middle finger, ring finger, and little finger or pinkie. According to different definitions, the thumb can be called a finger, or not. English dictionaries describe finger as meaning either one of the five digits including the thumb, or one of the four excluding the thumb (in which case they are numbered from 1 to 4 starting with the index finger closest to the thumb). Anatomy
Skeleton
The thumb (connected to the trapezium) is located on one of the sides, parallel to the arm. The palm has five bones known as metacarpal bones, one to each of the five digits. Human hands contain fourteen digital bones, also called phalanges, or phalanx bones: two in the thumb (the thumb has no middle phalanx) and three in each of the four fingers. These are the distal phalanx, carrying the nail, the middle phalanx, and the proximal phalanx. Joints are formed wherever two or more of these bones meet. Each of the fingers has three joints:

metacarpophalangeal joint (MCP) – the joint at the base of the finger
proximal interphalangeal joint (PIP) –  the joint in the middle of the finger
distal interphalangeal joint (DIP)  – the joint closest to the fingertip.Sesamoid bones are small ossified nodes embedded in the tendons to provide extra leverage and reduce pressure on the underlying tissue. Many exist around the palm at the bases of the digits; the exact number varies between different people.
Mees lines or Aldrich–Mees lines, also called leukonychia striata, are white lines of discoloration across the nails of the fingers and toes (leukonychia). Presentation
They are typically white bands traversing the width of the nail. As the nail grows they move towards the end, and finally disappear when trimmed. Causes
Mees lines appear after an episode of poisoning with arsenic, thallium or other heavy metals or selenium, opioid MT-45, and can also appear if the subject is suffering from kidney failure. They have been observed in chemotherapy patients. Eponym and history
Although the phenomenon is named after Dutch physician R. A. Mees, who described the abnormality in 1919, earlier descriptions of the same abnormality were made by Englishman E. S. Reynolds in 1901 and by American C. J. Aldrich in 1904. See also
Leukonychia
List of cutaneous conditions
Muehrckes nails – a similar condition, except the lines are underneath the nails and so do not move as the nail grows

References


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