The elephant appendicular skeleton includes the fore or thoracic limbs and hind or pelvic limbs. The both are arranged in an almost vertical position under the body, similar to apillar or leg of a table rather than being in the angular position seen in many other quadraped mammals The legs are built to support great weight. The marrow cavities are lacking in the elephant long bones but there iss a network of the dense cancellous bone which contain hemopoietic cells responsible for manufacturing blood cells. This structure makes the bones stronger and better able to withstand pressure than if they contained a marrow cavity.. A special structure in the plantar region of the foot to increase support for the massive weight and gaits of the elephant is called the cushion pad. The plantar surface of the elephant foot is covered with thick keratin layer. Elephants can walk, run and swim, however they do not trot, canter, gallop and jump. Normally an elephant gait involves lifing two feet on one side of the body together while the two feet on the other side remain on the ground (a rack gait). .The speed of elephant gaits varies from slow to quite fast, and elephants can outrun most humans.. Elephants can remain standing for long periods because of the position of bones and limbs.
Figure 3. (Left) Elephant carpal bone (modified from Shoshani J., 1992) (Right) Structure of an elephant foot (modified from Redmond I., 1997)
Muscular structures of an elephant are large, including muscle fibers, tendons and ligaments. There are three types of muscle, voluntary (skeletal) and involuntary ( smooth and cardiac), as is the case in all mammals. Their function effects the movements of the bones, when stimulated by signals from nerve fibers. The muscles are nourished by their vascular supply.
The elephant trunk is an interesting organ.It is composed of muscles, vessels, nerves, fat and other connective tissues, and skin. The trunk evolved from fused muscles of nose, upper lip and cheeks. It contains no bone or cartilage, although cartilage is found around the nostrils and at the base of the trunk. The muscles are include superficial and internal muscles. The total number of a muscles is approximately 150,000.. Superficial muscles run longitudinally along the dorsal, ventral and lateral aspects of the trunk. The internal muscles are deep to the superficial mucles and include radial muscles and transverse muscles. The two nostrils are separated by a membranous septum and are connected to openings in the frontal aspect of the cranium. The functions of the trunk include feeding, watering, dusting, smelling, touching, communicating (touch and sound promoter), defense and others. The trunk of an adult Asian elephant can hold about 10 liters of water.
Figure 4. The structure of elephant trunk (modified from Redmond I., 1997)
The skin of elephant is not equally thick at all locations of the body. The thin skin is 1.8 millimeters, found in the ear, around the mouth and anus. The thicker skin is found on the head, back and buttock. This skin can be 2.5-3.5 centimeters or more thick. The skin is a highly sensitive organ with a rich nerve supply. Like other mammals, the skin is composed of two major layers (dermis and epidermis), which include glands and hair follicles. The color of skin is darker (brown or reddish) in African elephants and lighter in Asian elephants (gray). The Asian elephants have localized areas of depigmentation on their forehead, neck, ears and forelimbs. Normally the skin is covered with dust, soil or mud for prevent insect bites, ultraviolet radiation damage and moisture loss.
Hair can found of a body of baby and young elephant, especially on the head and back. Adult elephants, have less hair than young elephants and African elephants have less hair than Asian elephants. Hairs concentrate around eyes, mouth, chin, the ear opening and the end of the tail. Hair color varies from brownish, to brown, black, gray or white. Nail and plantar pad The structure of elephant nails is similar to other mammals. Elephants stand on the plantar surface of their foot with the cushioned pad supporting the heavy weight. The nails grow about 1 centimeter per month. The plantar surface of the foot is covered with keratinized layer, called the keratinized sole, which is approximately 4-12 millimeters thick and grows at a rate of 0.5-1 centimeters per month. Sweat gland The elephants lack of sweat glands over most of their body, and cannot use them for thermoregulation. Some sweat glands may be seen in coronet line of the toenail. The ears are used as the primary means of thermoregulation dispersing heat through radiation and with the assist of flapping the ears to move air to increase the efficiency of the radiator. Temporal or musth gland An adapted sebaceous gland is located midway between eye and ear on the temple on both sides of the head. Its opening or orifice can be visualized with the unaided eye. The glands are covered with skin that is 2 or more cm thick.. The glands produce chemical substances important in elephant reproduction. The secretion is oily and smells foul when secreted through the glands opening. Elephants in musth areaggressive, especially males. Females in musth are normally not aggressive.
Figure 5. (Left) The temporal or musth gland structures(modified from Shoshani J., 1992), and microscopic structure (x 40) (Right) The opening of temporal
The respiratory tract of elephants is comprised of the conducting portion (external nares, nasal tubes, internal nares, pharynx, larynx and trachea) and the respiratory portion (bronchi, bronchioles, alveolar duct and alveolar sac in lung). Sound is produced from larynx. The lungs are attached to the thoracic walls and diaphragm, oblitherating the potential pleural space normally maintained in negative pressure to assist breathing in other mammals. . Unlike most other mammals, elephants rely on intercostals and diaphragmatic muscle movement alone to inflate and deflate the lungs. If there is an impediment in the muscular excersion of the key muscles in respiration for the elephant, the resulting dyspnea is severe. For example, long periods of sternal recumbency increase abdominal pressure thereby limiting diaphragm motion. Elephants poorly tolerate sternal recumbency and assume lateral recumbency when they lay down. This can be observed at times when elephants sleep.