MetacarpalsFive bones of the palm, one behind each finger.
PhalangesFourteen finger bones: two in the thumb, three in each finger.
Cat foreleg 6
HumerusThe one bone of the upper foreleg.
RadiusOne of the two forearm bones, on the thumb side.
UlnaThe second forearm bone. Its end forms the point of the elbow.
CarpalsSeven small wrist bones in two rows.
MetacarpalsFive bones of the paw, numbered from the thumb.
PhalangesThe toe bones. The last one in each toe carries the claw.
Whale flipper 6
HumerusShort and very stout, with a ball-shaped head.
RadiusShort, broad and flat.
UlnaShort, broad and flat, like the radius beside it.
CarpalsMany-sided wrist bones packed side by side.
MetacarpalsOne short bone at the base of each finger.
PhalangesFar more finger bones than in any other mammal.
Bat wing 6
HumerusLong and slender.
RadiusThe main bone of the forearm, and very long.
UlnaOnly a short splint, joined to the radius at the elbow.
CarpalsSmall wrist bones. Some are joined into one.
MetacarpalsVery long in four fingers. They spread the wing.
PhalangesThin bones at the finger ends. The short thumb has a claw.
Bird wing 6
HumerusThe one bone of the upper wing.
RadiusOne of the two bones of the forearm.
UlnaThe other forearm bone, beside the radius.
CarpalsOnly two free wrist bones are left.
CarpometacarpusWrist and palm bones fused into a single bone.
PhalangesThe bones of three short fingers.
How this list was compiled: Each bone on each animal checked on 2026-10-01 in two sources. W. H. Flower, An Introduction to the Osteology of the Mammalia (1885, public domain), https://archive.org/details/introductiontoos1885flow. J. Reighard and H. S. Jennings, Anatomy of the Cat (1901, public domain), https://archive.org/details/anatomyofcat00reig. T. J. Parker and W. A. Haswell, A Text-book of Zoology, volume 2 (1910, public domain), https://archive.org/details/textbookofzoolog02parkuoft. O. Charnock Bradley, The Structure of the Fowl (1915, public domain), https://archive.org/details/structureoffowl00braduoft. Wikipedia: Upper limb, Bat, Bird wing, Homology (biology), https://en.wikipedia.org/wiki/Homology_(biology). University of California Museum of Paleontology, Understanding Evolution, https://evolution.berkeley.edu/evolution-101/the-history-of-life-looking-at-the-patterns/homologies-and-analogies/. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
This comparative anatomy quiz shows five forelimbs, each with its shoulder at the left: a human arm, a cat foreleg, a whale flipper, a bat wing and a bird wing. A ring marks one bone; pick its name from four.
Read the full guide
One plan, five limbs
From the shoulder out, every limb has one upper bone, the humerus; two forearm bones, the radius and the ulna; wrist bones, the carpals; then metacarpals and phalanges. Each bone keeps one tint in all five drawings. Parts built on a shared plan like this are called homologous structures.
What changes from limb to limb
A whale's arm bones are short and flat, and its longest fingers have many more bones than three. A bat's ulna is a short splint, and four of its metacarpals are very long. In a bird the wrist and palm bones are fused into one bone, the carpometacarpus.
Find the radius first. It is on the thumb side, drawn above the ulna in every limb.
Questions and answers
What is comparative anatomy?
The study of how the body structures of different species are alike and how they differ. The bones of the forelimb are its best-known example.
What are homologous structures?
Parts of different animals that are alike because a shared ancestor passed them down, even when they now do different jobs. A human arm, a whale's flipper and the wings of bats and birds are a common example.
Do bats and birds have the same wing bones?
Both have a humerus, a radius and an ulna. A bat's wing is skin stretched between very long finger bones and the arm. A bird's wing is made of feathers along the arm, and its fingers are reduced to three.
Does a whale flipper have finger bones?
Yes. Inside the flipper are a humerus, a radius, an ulna, wrist bones and fingers. In whales a finger can have more than three bones, which is true of no other mammal.