Clavicle Bone
The clavicle is the prominent bone that goes across your upper chest, from shoulder to shoulder, above the breasts and below the neck. We often refer to it as our collar bone. It is the upper delimiter of the breast. It has a distinctive notch in the center, directly above the sternum and below the trachea.

Ribs
When breast implants are used, they may either be located between the Pectoral muscles and the ribs (submuscular), or in front of the Pectoral muscles, but behind the breast tissues (subglandular). The lower attachment of the breast to the chest wall is usually near the sixth rib when a breast reaches full maturity at the end of puberty. This attachment point (in relation to the sixth rib) actually changes over a woman's lifetime, moving in the downward direction as she ages. Note that this is only the attachment point, and the breast ptosis or sagging is a totally separate issue.

Fatty Tissue
One third of the average sized adult breast of a non-lactating woman consists of fatty tissue. Larger adult breasts usually only contain more fatty tissue. Smaller than average breasts still contain the same amount of Glandular (milk producing) tissue, but have less fatty tissue. Poor nutrition will prevent the storage of excess fat in the breasts, and may result in a sagging (pendulous) effect.

Pectoralis (Pectoral) Muscles
These connect between the chest and the arms. They may be affected or partially removed during a radical mastectomy, affecting the use of the arm that is involved. These muscles are what will develop when chest exercises are done to increase breast size. A minimal effect to the breast size will result, with a possibility of a negative overall effect due to an increase in physical activity during the special exercises removing some of the fatty tissues from the breasts.

Gland Lobules
Also known as acini or alveoli, these are the actual source of breast milk. They develop during puberty to a certain degree, and then complete their development during pregnancy. Lobular development causes the breasts to expand. The final development occurs during pregnancy, and allows the production of milk after giving birth. Most breasts of the same cup size have the same average number of lobules, and they are grouped into 15 to 25 lobes. As a woman approaches menopause, the lobules start to atrophy, allowing a reduction in the density of the breasts. They may be replaced with fatty tissue, further softening the breast; a process called involution.

Ampulla (Lactiferous Sinus)
This is an enlarged area in the Lactiferous Duct that maintains a small reserve of milk that will be immediately available to the infant that is placed at the breast. It will maintain his/her interest until the Lobules are able to produce and release more milk. Pressure is placed directly onto these to manually express milk from the breast, not on the nipple.

Suspensory Ligaments
Often referred to as Cooper's Ligaments, these are the fibrous connections between the inner side of the breast skin and the pectoral muscles. Working in conjunction with the fatty tissues and the more fibrous lobular tissues, they are largely responsible for maintaining the shape and configuration of the breast. They bear a major portion of the task of preventing breast ptosis (sagging).

Lactiferous Ducts (milk ducts)
These gather the milk from the lobules and deliver it to the nipple. Each lobe usually has its own ductal system.

Inframammary Ridge
Located at the junction between the lower side of the breast and the chest wall, it is a more dense area that is easily felt when lying on your back. This will often thicken with age. It might be (and often is) confused with a mass or lump during a Breast Self-Examination.