The intermammary cleft or intermammary sulcus or sulcus intermammarius is a surface feature of males and females that marks the division of the two breasts with the sternum (breastbone) in the middle. The International Federation of Associations of Anatomists (IFAA) uses the terms "sulcus intermammarius" or "intermammary cleft" when referring to the area between the breasts. Etymology "Intermammary" ("inter", between + "mamma", breasts + "ry", place) means something that is located or performed between the breasts (example: intermammary intercourse). "Sulcus" is a Latin word that means a furrow or groove, commonly used to mean a fold, fissure or furrow of the brain (example: lateral sulcus). In popular usage the area is commonly referred to as a cleavage of breasts. In surgical parlance, the cleavage or intermammary cleft is also known as the "medial definition" or "medial fold" of breasts. An imaginary line between the nipples that crosses the intermammary cleft, serving as a landmark for some CPR procedures, is known as the "intermammary line". Anatomy Skin At the midline of the breast—the intermammary cleft—a deep layer of superficial fascia (lowermost layer of the skin) is firmly attached to the pectoral fascia (outer side of chest muscles) and the periosteum (bone membrane) of the sternum. It forms a shelving edge that supports the breasts. Muscles The Sternalis muscle is an anatomical variation that lies in front of the sternal end of the pectoralis major runs along the anterior aspect of the body of the sternum. The sternalis muscle often originates from the upper part of the sternum and can display varying insertions such as the pectoral fascia, lower ribs, costal cartilages, rectus sheath, aponeurosis of the abdominal external oblique muscle. There is still a great deal of disagreement about its innervation and its embryonic origin. The sternal side (towards the breastbone) of the pectoralis major is distinct from the clavicular side (towards the collarbone), and the two are separated by a fascial interval. The sternal side is usually more robust and has a fiber orientation that best emulates the downward pull of the subscapularis muscle (armpit muscle). Ligaments A dense structure of Cooper's ligaments is medially inserted into the skin overlying the sternum, determining the shape of the breasts and intermammary sulcus. These ligaments helpful in supporting the breasts in an youthful disposition; loss of elasticity or attenuation of these ligaments results in ptosis (sagging) of breasts. Arteries Major blood supply