Dissection and roentgenographic analysis of the upper portion of the shaft and neck of the femur revealed the presence of a highly independent laminar, bony system, from ten to twelve centimeters long, which begins from two to four centimeters below the lesser trochanter and ends in fanlike fashion at the cartilaginous plate of the head. This proved to be the internal weight-bearing system of the proximal portion of the femur. This system undlergoes slow resorption in its distal portion after middle age, but never disappears; and on the roentgenogram it can be seen throughout life from its distal to its proximal end. Microscopically, it consists of a great number of laminae and bone cells, and a rich endosteal lining. It resembles the spongy laminae of the iliac bone,—hence the speed with which it is capable of new-bone formation. Mechanically, the internal weight-bearing system is a compression system, and during weighit-bearing it is to be founod almost in the vertical plane. The presence of tensile stresses is doubtful. Preceding adduction fractures, the internal weight-bearing system is resorbed and replaced by cortical bone in its entire distal portion. Its proximal end remains spongy, with laminar character. The separation occurs at the site where the spongy proximal portion begins and the distal cortical portion ends. In abduction fractures, the internal weight-bearing system suffers only trauma, but otherwise it is healthy and strong. This explains the rapid healing of such fractures. On the basis of the anatomy and pathology of the femoral neck, two types of fracture may be distinguished: (1) compression fractures, comprising the abduction, intermedial, and adduction fractures; and (2) subcapital separations, represented by most fractures of the aged. The prognosis of the compression fractures is good, if the fragments are kept in good apposition andl fixation in plaster, in Russell traction, or by nailing. For the treatment of the adduction fractures, a method with a perforated (sieve) sublay graft has been developed.