Boat or Bateau: forms a strong horizontal line from shoulder to shoulder and is excellent for medium and broad-tapered shoulders. It should be avoided by broad-square shoulders until the boatneck is interrupted (crossed) with a chain or necklace which breaks the long horizontal line.
The two shoulders are located beneath the head connecting the arm and the chest. Each shoulder consists of 2 bones, the clavicle and the scapula, and collectively both shoulders account for 4 bones in the body. http://www.learnbones.com/shoulder-bones-anatomy/