Sternum

The sternum or breastbone is a long flat bone shaped like a necktie located in the center of the chest. It connects to the ribs via cartilage, forming the front of the rib cage, and thus helps to protect the heart, lungs,and major blood vessels from injury. The sternum consists of three regions: the manubrium, the body, and the xiphoid process.

The word sternum originates from the Greek στέρνον, meaning chest.

Structure

The sternum is a long, flat bone, forming the middle portion of the front of the chest. The top of the sternum supports the clavicles (collarbones) and its edges join with the costal cartilages of the first seven pairs of ribs. The inner surface of the sternum is also the attachment of the sternopericardial ligaments. Its top is also connected to the sternocleidomastoid muscle. The sternum consists of three main parts, listed from the top:

In its natural position, the sternum is angled obliquely, downward and forward. It is slightly convex in front and concave behind; broad above, shaped like a "T", becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. In adults the sternum is on average about 17 cm, longer in the male than in the female.

Sternum (arthropod anatomy)

The sternum (pl. "sterna") is the ventral portion of a segment of an arthropod thorax or abdomen.

In insects, the sterna are usually single, large sclerites, and external. However, they can sometimes be divided in two or more, in which case the subunits are called sternites, and may also be modified on the terminal abdominal segments so as to form part of the functional genitalia, in which case they are frequently reduced in size and development, and may become internalized and/or membranous.

Ventrites are externally visible sternites. Usually the first sternite is covered up, so that vertrite numbers do not correspond to sternid numbers.

The term is also used in other arthropod groups such as crustaceans, arachnids and myriapods. Sternites on the pleon (abdomen) of a crustacean may be referred to as pleonsternites. These are the sites of attachment of the pleopods (swimming legs). In spiders, the sternum is the ventral part of the cephalothorax.

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