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Physical anthropologists study human biological variation in the past and present. They are not only interested in the physical aspect of the body but also how biology, culture and environment interact to produce variation. Part of this variation is found in the bones and teeth. Since these are the hardest parts of the body, they have the greatest chance of being found in the archaeological record. Thus they form the bulk of direct information about the biological course of human evolution.
Structure and Function of Bone
The shape of the skeleton is a reflection of the functions that it performs. Like the steel girders in a skyscraper, it provides a framework and support for the body. Vital organs (such as the brain) are protected by being enclosed in bone. Movement is accomplished by combination with the muscular and nervous system. The muscles attach to the bones and form a system of levers. As the muscles grow, they influence the shape of the skeleton. Most of the projections, nodules, and ridges that you will see were created by the muscles sculpturing areas for attachment. The skeleton is also responsible for the manufacture of blood cells and for the storage of various minerals so that the body can obtain them even if the diet is temporarily deficient.
Bony tissue is about 50% water and 50% solid matter. Most of the solid material is cartilage which has been hardened by the impregnation of inorganic salts, especially carbonates and lime phosphate. As one ages, the proportion of lime increases so that the bones become more brittle and break more easily.
In a living individual, the appearance of bones is very different from skeletonized remains. They are covered with a white fibrous membrane called the periosteum. Cartilage forms the cover around the joints. Muscle fibers interlace with the periosteal fibers to anchor both together. In a growing individual, the inner layer of the periosteum contains the bone forming cells call osteoblasts. Immediately beneath the periosteum is a dense layer of compact bone. Under it lies the cancellous bone. It is much less dense and has the appearance of a spidery framework to give it maximum strength with minimum weight. The extreme inside of the bone is the medullary cavity. It is surrounded by the endosteum, which is a condensed layer of marrow.
Microstructure of Bone
Under magnification the most notable features are concentric rings, holes, and spidery black regions. The latter dark areas called lacunae are the homes of the bone cells (osteocytes). The osteocytes are interconnected with blood vessels and nerves. These blood vessels and nerves run through the Haversian canals, which appear as holes in cross section. The light colored concentric rings are called lamellae. These represent the places of mineral deposit.
A number of terms are used when studying and researching the human skeleton. It is important to memorize these terms as they will be necessary in placing remains in the anatomical position, siding, and general observation.
Dorsal Back side of a human, upper side of an animal
Ventral Front side of a human, belly side of an animal
Lateral The sides, right and left
Median The middle
Peripheral The part nearest the surface
Proximal Near the main mass of the body
Distal Away from the main mass of the body
Medial Toward the middle
Cephalic Toward the head
Caudal Toward the tail
Superior Toward the head
Inferior Toward the feet
A few terms are also important to memorize regarding the movement that individual bones/muscles are involved in.
Flexion Bending of a limb
Extension Straightening of a limb
Abduction Pulling a limb away from midline
Adduction Pulling a limb toward midline
Rotation Movement of a limb around its own axis
Several anatomical features have specific technical terms that are used to describe them. Familiarize yourself with the list provided below.
Diaphysis Shaft of a bone
Epiphysis Ends or extremities of a bone, where growth takes place
Metaphysis Line of junction between the diaphysis and epiphysis
Tuberosity A rounded eminence or bulging of the bone
Process Marked projection, articulating bone projection
Spine Slender or pointed projection
Tubercle Small nodule
Linea A slight ridge of bone
Condyle An enlargement bearing an articular surface
Foramen Short perforation
Canal Long perforation
Aperture Opening on surface or space within a bone
Trochanter A large prominence for attachment of rotator muscles
Sulcus A groove
Sinus A cavity in bone lined with mucous membrane
Lip Margin of a groove, crest or line
Head A rounded, smooth eminence for articulation
Fossa A furrow or depression
Ramus A branch of bone
Symphysis An almost immovable joint; the line of junction between bones
Suture Seam, line of union in an immovable articulation
Crest Prominent ridge