The pectoralis major (from Latin pectus 'breast') is a thick, fan-shaped or triangular convergent muscle of the human chest. It makes up the bulk of the chest muscles and lies under the breast. Beneath the pectoralis major is the pectoralis minor muscle.

The pectoralis major is made up of 3 muscle bundles: the upper bundle (or clavicular), the middle bundle (or superior sterno-costal) and the lower bundle (or inferior sterno costal or abdominal)

Pectoralis minor muscle is a thin, triangular muscle, situated at the upper part of the chest, beneath the pectoralis major in the human body. It arises from ribs III-V; it inserts onto the coracoid process of the scapula. Its function is to stabilise the scapula by holding it fast in position against the chest wall.

• This lateral view is important to understand the ,, horizontal red line ,, in the techniques which begins outwards at the base of the axilla ,,.
• Also the separation between the clavicular head and the sterno costal heads of the pectoralis major , if made horizontal can be too helpful to draw the ,, red horizontal line ,,.

With vectors applied normal to the pectoralis major, because of the diffusion of the product which is oily, the pectoralis minor can be too involved .