Head - Caput humeri
The head of humerus, nearly hemispherical in form, is directed upward, medialward, and a little backward, and articulates with the glenoid cavity of the scapula.
The circumference of its articular surface is slightly constricted and is termed the anatomical neck, in contradistinction to a constriction below the tubercles called the surgical neck which is frequently the seat of fracture. Fracture of the anatomical neck rarely occurs.
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).