When we look at a dog, much of what we see is the result of the growth of the bones, muscles, joints, ligaments and tendons. The bones and muscles give the dog its general conformation or shape. In puppies we frequently use such terms as 'leggy,' meaning the legs appear longer than normal; or 'squatty,' suggesting short legs. The puppy may appear roly-poly or round, or it may appear long and spindly. In any event, these non-scientific terms attempt to describe how the young animal's bones and muscle tone have developed, or how they are developing.
A puppy is born with all the bones, joints, muscles, ligaments and tendons that it will ever have. All growth is due to an increase in size of these tissues, not to an increase in their number.
Bones, muscles, ligaments and tendons compose the bulk of an animal's body mass. Allowing for variations in tail length, there is an average of 319 bones in the dog skeleton.
Bones are complex, rigid, living organs that have their own supply of blood vessels and nerves. They are composed of minerals, primarily calcium and phosphorus. They provide both the framework for the body and protection for many delicate internal organs and structures. For example, the bones of the skull protect the brain and eyes while the breast plate (sternum) and ribs help protect the heart and lungs. Other bones, such as those of the limbs, function to provide support and locomotion. Bones of the internal ear structures function for neither protection nor support, but rather for sound transmission, allowing the dog to hear.
The bones of the legs grow from areas of immature bone located near the ends. These are called the growth plates, epiphyseal plates or simply the epiphysis. Growth plates are soft areas of the young bone that grow and add length to the bones. Growth plates provide growth to the bone until the puppy's bone growth is complete, usually by one year of age. At this time, the growth plates become hard with calcium and minerals and no longer function as areas of growth. This mineralization is referred to as a closing of the growth plates and indicates the end of significant bone growth. The young unmineralized growth plates are a weak area in the puppy's bone and are frequent sites for bone injury or fracture. Epiphyseal fractures are common near the wrist (carpus) and the knee (stifle).
The primary function of muscles is to bring about movement to all or a part of the dog's body. There are two types of muscles, smooth and striated. Smooth muscles are found within the internal organs such as the intestines, stomach, and bladder. These are not subject to voluntary or conscious control by the individual. They function automatically to satisfy the body's needs. Striated muscles are predominately attached to the skeleton. All of their movements are under the conscious control of the individual. They are involved with such things as walking, eating, tail wagging, eye movement, etc.
Muscles are connected to the bones by tough fibrous bands called tendons. Tendons begin on a muscle and end on a bone. A good example is the Achilles tendon, which connects the muscle of the lower rear limb (calf) to the bones forming the ankle.
Ligaments and joints
Ligaments connect bone to bone and are generally found spanning across joints. Joints are places where two bones meet or articulate with their ends covered by a layer of smooth cartilage. A joint consists of bones, muscles, ligaments, cartilage, and a lubricating joint fluid all enclosed by a tough joint capsule.