saddle joints: Joints that have the appearance of a saddle. The carpometacarpal joint at the base of the thumb is an example of a saddle joint.

sagittal planes: Imaginary vertical planes that are parallel to the midsagittal plane and divide the body into unequal left and right portions. There are many possible sagittal planes, so you should always give a reference point where the plane passes through.

scapula: The shoulder blade.

sciatic foramen: The opening in the posterior portion of the pelvis formed by the sciatic notch of the ischium and the sacrospinous and sacrotuberous ligament.

scoliosis : A rotation and lateral flexion of the spine that may twist and turn the thoracic cage.

sebaceous glands: Glands connected to the hair follicles. They produce sebum, which is an oily substance that helps keeps the hair flexible.

skeletal muscles: The muscles responsible for making the skeleton move. They’re voluntary muscles because you can control whether the muscles move.

stratum basale: Forms the deepest layer of the skin. The cells of this layer continuously divide and form new keratinocytes to replace the ones that are constantly shed. This layer also contains melanocytes, which are the cells that produce skin coloring.

stratum corneum: Dead, mature skin cells called keratinocytes. These cells are constantly shed and replaced by cells from the lower layers of the epidermis. These cells have lost most of their internal structures and organelles.

stratum granulosum: The area of the skin where keratin is formed. The cells in this layer also produce materials that prevent evaporation, which helps waterproof the skin.

stratum lucidum: Found in thicker skin; helps reduce friction between the stratum corneum and the stratum granulosum. It’s composed of dead, flattened cells.

stratum spinosum: Contains keratin-producing cells that were formed in the stratum basale.

subcutaneous layer: Area below the skin; underneath the cutaneous layer and is sometimes called the hypodermis or superficial fascia.

subserous fascia: The part of the fascia that lies between the body walls such as the thoracic wall and the membranes that line corresponding body cavities.

superficial: Closer to the surface. For instance, the skin is superficial to the muscles.

superior: Closer to the top of the head. For example, the nose is superior to the chin.

superior oblique muscle: The muscle that turns the eyeball inferiorly and laterally.

supination: Lateral rotation of the forearm so the palm faces anteriorly.

sympathetic stimulation: Causes bronchodilation and constricts the blood vessels.

synapse: The junction in the brain where nerve impulses pass.

synovial joints: A typical synovial joint includes bones covered in hyaline cartilage and a joint cavity lined with a synovial membrane and filled with synovial fluid. A durable fibrous joint capsule surrounds the joint. Some synovial joints also have fibrocartilaginous discs between the bones.