Poultry and mammals: structure of the dog

Mammals are highly organised warm-blooded animals: the body is covered with hair, there are an outer ear, milk and sweat glands, they feed young on milk, most give birth to live young, and the brain cortex has developed folds. Their structure is studied on the dog. The dog’s legs are under the body, so the body is raised from the ground; it walks on its toes. The head is joined by a movable neck, the third eyelid is small and hidden in the inner corner of the eye, and the outer ear is movable. The coat has two layers: a top layer of long, coarse guard hairs and an under layer of soft, short hairs; the under hairs trap air and keep heat. There are also long sensory whiskers. Most mammals have sweat glands: sweat cools the body and removes excess salts. The dog has few sweat glands (mostly on the paws), so in hot weather it cools by panting with its mouth open. The tips of the toes bear horny claws or hooves. The skeleton consists of skull, vertebral column, rib cage, limbs and girdles; the braincase is large. The column has neck (7 vertebrae), chest (12–15), lumbar (6 in the dog), sacral (3–4, fused to the pelvis) and tail parts. The lumbar vertebrae are movable, so the body bends at the loin. The dog’s collarbone is not developed. The teeth are of different kinds: wedge-shaped incisors, large cone-shaped canines and flat cheek teeth; on each side of each jaw one cheek tooth has become a carnassial tooth. The jaw muscles are very strong. Safety: do not approach unfamiliar dogs, do not put your hand to a dog’s mouth; if a dog bites, wash the wound with soap and water and go to a doctor at once (rabies vaccination may be needed).