Why don’t dogs draw in their claws like cats do?

In both dogs and cats the claws protect the ends of the toes and they are also used to increase the animal’s grip, for example when running (especially in the dog) and climbing (chiefly in the cat) and for attack and defense (again, mainly in the cat). In the dog the claws are stronger; in the cat they are sharper. It would appear that it is to keep the claws sharp, and to assist in the mechanics of climbing, that the cat is able to retract them into a protective sheath. The dog is unable to do this.

In both species there are four main toes, or digits, on each foot, and each toe consists of three bones (the phalanges) with joints between them. The horny claw (the equivalent of a human fingernail or toenail) is attached to the third of these, the last and smallest bone in the chain. Two strong elastic ligaments run between the second and third bones. In the cat there is a small recess on the outer face of the second bone at its front end so that at rest the third bone is pulled by these ligaments right the way back to lie alongside the second bone; when the bone is in this position the claw is back inside its sheath. In the dog there is no such recess, so the pull of the ligaments does not cause retraction of the claw.

On the underside of each toe runs a strong muscle tendon (the deep flexor tendon) which is attached to the third bone. A pull on the tendon moves this bone forwards and downwards in both species, but in the cat, where much more movement is possible, this results in the claw being unsheathed.

If the tracks of dogs and cats are examined it can be seen that the dog leaves claw marks in front of its digital pads, whereas there are no claw marks left by the cat because its claws are retracted while walking. Incidentally, the tracks of a dog can be distinguished from the similar tracks of a fox because its pads are larger and closer together and because the front edge of the outer pads extends beyond the back edge of the central pads.

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This entry was posted on Wednesday, June 10th, 2009 at 11:17 pm and is filed under Dog Supplies Q&A, Dog Supplies Tips. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.