THE FEMUR, OR THIGH BONE 



227 



Structure. The shaft of the femur is a cylinder of compact tissue, hollowed by a large med- 

 ullary canal. The cylinder is of great thickness and density in the middle third of the shaft, 

 where the bone is narrowest and the medullary canal well formed; but above and below this 

 the cavity gradually becomes smaller, owing to a separation of the layers of the bone into cancelli, 

 which project into the medullary canal and finally obliterate it, so that the upper and lower 

 ends of the shaft, and the articular extremities more especially, consist of cancellated tissue 

 invested by a thin, compact layer. 



The arrangement of the cancelli in the ends of the femur is remarkable. In the upper end they 

 are arranged in two sets. One, starting from the top of the head, the upper surface of the neck, 

 and the great trochanter, converge to the inner circumference of the shaft (Figs. 180 and 181); 

 these are placed in the direction of greatest pressure, and serve to support the vertical weight 

 of the body. The second set are filanes of lamella? intersecting the former nearly at right angles, 

 and are situated in the line of the greatest tension that is to say, along the lines in which the 

 muscles and ligaments exert their traction. In the head of the bone these planes are arranged 

 in a curved form, in order to strengthen the bone when exposed to pressure in all directions. In 



FIG. 181. Longitudinal section of head and neck of femur. 



the midst of the cancellous tissue of the neck is a vertical plane of compact bone, the femoral 

 spur (calcarfemorale), which commences at the point where the neck joins the shaft just external 

 to the lesser trochanter, and extends in the direction of the digital fossa (Fig. 182). This mate- 

 rial!/ strengthens this portion of the bone. Another point in connection with the structure of the 

 neck of the femur requires mention, especially on account of its influence on the production of 

 fracture in this situation. It will be noticed that a considerable portion of the great trochanter 

 lies behind the level of the posterior surface of the neck; and if a section be made through the 

 trochanter at this level, it will be seen that the posterior wall of the neck is prolonged into the 

 trochanter. This prolongation is termed by Bigelow the true neck, 1 and forms a thin, dense 

 plate of bone, which passes beneath the posterior intertrochanteric ridge toward the outer sur- 

 face of the bone. In the lower end the cancelli spring on all sides from the inner surface of the 

 cylinder, and descend in a perpendicular direction to the articular surface, the cancelli being 

 strongest and having a more accurately perpendicular course above the condyles. In addition 



1 Bigelow on the Hip, p. 121. 



