They are the world’s smallest breed of toy dog. Picture: Pixabay

London - The chihuahua hails from the Mexican state of the same name.

They are the world’s smallest breed of toy dog, weighing in at anything from 2lb (907g) to 6lb (2.7kg) - barely a third of the average cat.

Newborn puppies can fit in the palm of a human hand; litters usually number four.

The dogs have such fragile necks that owners are advised to use harnesses rather than leads to protect them from injury.

Relative to their bodies, chihuahuas have the biggest brains in the canine world.

They were worshipped by the Aztecs and highly prized because of their size and intelligence.

Like human babies, chihuahuas have a soft spot on their heads, which may last for life.