cartilage [key], flexible semiopaque connective tissue without blood vessels or nerve cells. It forms part of the skeletal system in humans and in other vertebrates, and is also known as gristle. Temporary cartilage makes up the skeletal system of the fetus and the infant, forming a model for later replacement by bone as the body matures. Permanent cartilage remains throughout life, as in the external ear, nose, larynx, and windpipe (or trachea). Cartilage is also present at the joints, where it reduces friction and imparts flexibility. There are three major types of cartilage appearing in vertebrates. The most common is hyaline cartilage, which composes the pre-skeletal model and is found in adults at the joints, in the nose, and in several internal organs. Elastic cartilage is found in several parts of the ear and in the epiglottis, and is the most pliable type of cartilage. Fibrocartilage is found in the intervertebral disks, and is an extremely resilient tissue.
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