A typical animal carcass is composed of:

Muscle
Epithelial Tissue
Nervous Tissue
Connective Tissue
Adipose Tissue
Cartilage
Bone
Blood and Lymph

Muscle

There are three types of muscle found in an animal carcass: skeletal muscle, smooth muscle, and cardiac muscle. Skeletal muscle (also known as voluntary muscle) makes up 35 to 65 percent of the carcass weight of a typical animal. These are the muscles which allow an animal to move its body at will. They can be attached to bones, ligaments, fascia, cartilage, or skin. Each long, thin, highly specialized muscle cell is called a muscle fiber. Although a muscle fiber may be several centimeters in length, they are extremely thin with diameters ranging from 10 micrometers to 100 micrometers. Skeletal muscle has a microscopic transverse banding pattern and is sometimes referred to as striated muscle.

There are two types of muscle fibers: red and white. While most muscles are composed of both red and white fibers, the intensity of the muscle color is due to the proportion of red fibers to white fibers. Muscles which appear red (such as the leg muscles of chicken and turkeys) have a higher proportion of red fibers than muscles which appear white (such as the breast muscles of chicken and turkey). Red muscle fibers have a higher myoglobin content which gives them their red color.

Smooth muscle is much less abundant. It is primarily found in the walls of arteries, lymph vessels, and in the gastrointestinal and reproductive tracts.

Cardiac muscle is found in the heart of the animal. It has the unique ability to contract rhythmically from early embryonic life until death. Like the skeletal muscle, it has microscopic banding (striations).

Epithelial Tissue

Relative to the other tissue types, there is very little epithelial tissue in the animal body. It forms the linings of external and internal surfaces of the body and some of the organ systems. Much of it is removed during slaughter and processing. The epithelial tissue remaining in the carcass is associated with the blood and lymph vessels as well as the edible organs such as the kidney and liver. In chickens the epithelial tissue under the skin gives fried chicken its characteristic flavor and crispiness.

Nervous Tissue

Nervous tissue makes up the peripheral and central nervous system of the animal. Although nervous tissue constitutes only about one percent of meat, its function immediately before and during slaughter has great influence on final meat quality.

Connective Tissue

Connective tissue holds the animal body together. Although a wide variety of tissues such as adipose tissue (fat), cartilage, and bone are considered to be connective tissues, Connective tissue proper such as tendons and ligaments are the tissues that usually come to mind when one thinks of connective tissue.

Connective tissue proper consists of a structureless mass called ground substance plus embedded cells and extracellular fibers. The lubricating fluid found in joints (synovial fluid) is one example of a ground substance. Ground substances generally function as lubricants, intercellular cementing substances, and can also be found in cartilage and bone.

There are two types of extracellular fibers which are connective tissue proper. Tendons are one example of extracellular fibers which are dense and uniformly arranged in bundles. Two well known types of extracellular fibers are collagen and elastin. Collagen is the most abundant protein in the animal body constituting 20 to 25 percent of total body protein. It is the major component in tendons and ligaments and is also found in bones, cartilage, and other tissues and most importantly, muscle.

Collagen plays an important role in meat tenderness. It is more soluble in young animals than it is in older animals and the collagen fibers of young animals have less tensile strength than the collagen fibers of older animals. The strength of the collagen fibers in the muscle of older animals makes their meat more resistant to shearing and chewing and hence, less tender.

Elastin is a rubbery, connective tissue protein which is present throughout the body in ligaments and arterial walls as well as a number of organs including muscle. Aggregations of elastin fibers (such as in ligaments) can be recognized by their characteristic yellow color. Because elastin is very insoluble and resistant to digestive enzymes it contributes little or nothing to the nutritive value of meat.

Adipose Tissue

Adipose tissue is fat. The bodies of many animals species have two types of fat: white fat and brown fat. Most adipose tissue is white fat, but brown fat is present at birth, especially around the kidneys. Most brown fat is converted to white fat a few weeks after birth, but in some animals persists into adulthood.

Cartilage

Cartilage along with bone provide the supportive structure for the animal body. Most bone is initially formed as cartilage during embryonic development and is later converted to bone. However, not all cartilage is converted to bone. Cartilage can be found in many places throughout the body including the surfaces of bones at joints, the ventral ends of ribs, between vertebrae, in the ear and many other locations.

Bone

Bones are an important part of the animal body as they provide the main structural support for the body. In addition, they also serve as storage sites for calcium, magnesium, sodium and other ions. Red blood cells, white blood cells, and platelets are produced in the bone marrow.

Blood and Lymph

Blood normally constitutes about 7 percent of the body weight of mammals. Blood consists primarily of three types of blood cells and the plasma in which they are suspended. The three types of blood cells are platelets which stop bleeding by causing clot formation, red blood cells which carry oxygen and nutrients throughout the body, and white blood cells which fight infection.

Lymph is a fluid which circulates continually and passes through all tissues, organs, and lymph nodes of the body. Lymph helps to carry dissolved nutrients to the body's tissues as it diffuses through very thin capillary walls. It also plays a part in the body's immune defense as it flows through lymph nodes which filter out harmful foreign particles such as bacteria and cancerous cells.