The American Kennel Club standard for the Chihuahua specifies a "well rounded 'apple dome' skull." While the apple dome skull is the ideal, it's not the only Chihuahua head type. The deer-head Chihuahua doesn't meet the breed standard, but that's not an issue for people who don't show their dogs.
Other than head shape and ear length, deer-head Chihuahuas don't differ from their apple-headed kin. The deer-head Chis have longer noses and sharper muzzles, with sloping foreheads. The ears are longer and head outward. As the name implies, their heads resemble those of deer, or perhaps fawns. Like the apple-head, the deer-head can appear in a variety of colors and have a short or long coat. At maturity, Chis generally weigh between 4 and 6 pounds. Since deer-heads can't show competitively, they might be slightly larger, perhaps 7 or 8 pounds. The AKC doesn't permit Chis over 6 pounds to compete in dog shows.