The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.

Terminology

The term "muzzle

Muzzle

A muzzle may be:* the snout of an animal* Muzzle , a device that covers an animal's snout* Muzzle , the mouth of a firearm* Muzzle , a song on The Smashing Pumpkins album Mellon Collie and the Infinite Sadness...

", used as a noun

Noun

In linguistics, a noun is a member of a large, open lexical category whose members can occur as the main word in the subject of a clause, the object of a verb, or the object of a preposition .Lexical categories are defined in terms of how their members combine with other kinds of...

, can be ambiguous. It can refer both to the protruding part of the face itself, and also to a type of apparatus placed over the protruding part to prevent the animal from biting or eating, often used before and after horse races or to control dog

Dog

The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...

s. See animal muzzle for the latter meaning.

The wet, naked surface around the nostrils of the nose is known as the rhinarium

Rhinarium

The rhinarium is the moist, naked surface around the nostrils of the nose in most mammals. In actual scientific usage it is typically called a "wet snout" or "wet nose" from its moist and shiny appearance...

 (colloquially this is the "cold wet nose" of some animals). The rhinarium is often associated with a stronger sense of olfaction

Olfaction

Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...

.

Snout of dogs

The muzzle begins at the stop, just below the eyes, and contains the dog's nose and mouth. In the domestic dog, most of the upper muzzle contains organs for detecting scents. The loose flaps of skin on the sides of the upper muzzle that hang to different lengths over the mouth

Mouth

The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....

 are called flews. The snout is considered a weak point on most animals: because of its structure, an animal can be easily stunned,snapped or even knocked out by applying sufficient force.

It is innervated by one of the twelve pairs of cranial nerves. These nerves start in the brain and emerge through the skull to their target organs. Other destinations of these nerves are eyeballs, teeth and tongue.

The muzzle shape of a domestic dog ranges in shape depending upon the breed

Dog breed

Dog breeds are groups of closely related and visibly similar domestic dogs, which are all of the subspecies Canis lupus familiaris, having characteristic traits that are selected and maintained by humans, bred from a known foundation stock....

, from extremely long and thin (dolichocephalic), as in the Rough Collie

Rough Collie

The Rough Collie is a long coated breed of medium to large size dog that in its original form was a type of collie used and bred for herding in Scotland. Originating in the 1800's, it is now well known through the works of author Albert Payson Terhune, and through the Lassie novel, movies, and...

, to nearly nonexistent because it is so flat (extreme brachycephalic), as in the Pug

Pug

The pug is a "toy" breed of dog with a wrinkly, short-muzzled face, and curled tail. The breed has a fine, glossy coat that comes in a variety of colors, and a compact square body with well-developed muscle. They have been described as multum in parvo , referring to the pug's personality and...

. Some breeds, such as many sled dogs and Spitz

Spitz

Spitz-type dogs are a type of dog, characterized by long, thick, and often white fur, and pointed ears and muzzles...

 types, have muzzles that somewhat resemble the original wolf's in size and shape, and others in the less extreme range have shortened it somewhat (mesocephalic) as in many hounds.

Snout of other mammals

Snouts are found on many other mammals in a variety of shapes. Some animals, including ursines and great cats, have box-like snouts, while others, like shrews, have pointed snouts. Pig snouts are flat and cylindrical.
Despite the opinion of some disreputable horse handlers, horses indeed have snouts. Sometimes a horse's snout can be referred to as it's "muzzle", although snout is the preferred terminology.

Snout of invertebrates

Some freshwater and marine (for example Eustrombus gigas) gastropods have snouts.