The skin is formed by two main layers: epidermis and dermis.
At glands located in the dermis (sebaceous - lubricate and waterproof the fur and produce odorous substances used in communication between animals, sweat - aid in temperature regulation and salt excretion, and mammary - usually more numerous than the average number of pups per litter) are one of the most striking aspects of mammalian lining.
The dog, cat and mouse do not have sweat glands. The dog's panting breath and the cat's licks on itself help cool the body.
Below the dermis, with the blood vessels that feed the epidermis and sensory nerves, there is a layer of subcutaneous fat, depending on the animal's habitat.
The set of hairs is called coatwhere each one grows from a follicle, such as bird feathers or reptilian scales. The fur is a succession of cells fortified with keratin. The coat is always composed of two types of hair: one inner, soft and insulating, and the other outer, thicker, which protects the body and gives color, allowing camouflage.
Some species have reduced hair coverage, but they are always changed periodically (each hair is changed individually, forming a new one from the same follicle).
Other structures are produced by the epidermis, such as claws, nails and hooves (which grow permanently from the base to compensate for wear), as well as horns and horns (with bone center and perms) and frames (fall annually).
The rhinoceros horn is a particular case of these structures, for although it does not fall annually it is composed of a dense tangle of hair.
The skeleton is fully ossified, with cartilage remaining only in the joint areas.
Horns and horns of various ungulate mammals
The muzzle is usually narrow. The trunk has ribs attached to the sternum, forming a rib cage very efficient in breathing movements.
Mammals typically have four legs (except cetaceans, where there are no hind limbs) with 5 fingers (or less) with fleshy claws, nails, hooves or pads, and are adapted to variously to walk, run, climb, dig, swim or fly.
Skeleton of a dog
The four-legged gait is the most common, but there are many bipedal species, such as kangaroos or humans.
Associated with the mode of travel is the form of paw contact with the ground: the animals plantigrades (bears, for example) rest the heel, metapode, and toes on the floor, while the digitigrades (canids, for example) only support their fingers.
The ungulates (horses, for example) only support the tip of one or two fingers. In marsupials the second and third fingers of the hind limbs are fused, giving rise to a single digit with two claws.
A) Plantigrade B) Digitigrade C) Ungulate.
The extremities are located below the body rather than sideways as in reptiles, which not only better supports the body weight but also allows for greater speed and reflexes.
Speed is also associated with the flexibility of the spine (cheetah, for example, adds about 30 km / h to its maximum speed due to the spring effect of its spine) and the increase in the length of the lower limbs (gazelles, for example). example).
The sense organs and the brain are very developed.
Some mammals have more developed senses than others.
The bat, for example, has great hearing; the jaguar has a keen sense of smell and the cat has excellent eyesight. Tactile information comes not only from the surface of the body, but also from whiskers. In language are located receptors of taste in specialized papillae.
Mammals are considered intelligent animals, although intelligence is difficult to define. Intelligence is generally considered to be the learning ability associated with behavioral flexibility. These capabilities allow you to solve problems related to invasion of new habitats and prey capture, for example.