684 MAMMALIAN ANATOMY 



the longest bone in the skeleton. Like the humerus, it has an extended 

 range of motion, but when the animal is standing at rest its direction 

 is more or less oblique from above downward and forward. The femur 

 is almost cylindrical for most of its length, which is twelve to fourteen 

 times its average width, but is expanded at the upper and lower ends, 

 where muscles and ligaments are attached around the joints. It may 

 be divided into three parts, the upper extremity, the shaft, and the 

 lower extremity. 



The Upper Extremity (Fig. 528) is not sharply divided from the 

 rest of the bone ; it is, however, more than twice as wide as the shaft, 

 but from before backward very little if at all thicker. It supports 

 three well-marked prominences, the head with its neck and the two 

 trochanters. 



The head is the inner angle of the upper end of the femur 

 prolonged upward, forward, and inward. It is nearly globular, smooth, 

 and covered with cartilage. Its inner surface is marked just behind 

 and below the middle by a deep rounded or oval pit, wherein is 

 inserted the ligamentum teres, or round ligament, which unites the 

 bone to the acetabulum of the innominate. The smooth surface of the 

 head is distinctly defined in front and below from the neck, but behind 

 arid above it is prolonged for some distance outward on the neck. 



The neck separates the head from the shaft, and affords insertion 

 for the capsular ligament of the hip-joint. It is a constriction which, 

 inasmuch as the head is almost at right angles to the rest of the upper 

 extremity, encircles the bone in a plane very little oblique to the plane 

 of the long axis of the shaft. The neck passes above outward, almost 

 horizontally, to the greater trochanter ; in front and on the inside it is 

 continuous with the anterior and inner surfaces of the shaft ; behind 

 it is separated from the greater trochanter by the digital fossa, and 

 from the shaft by the posterior intertrochanteric line and the lesser 

 trochanter. 



The greater trochanter is the extension upward, outward, and 

 backward of the external angle of the upper end of the bone. It is 

 pyramidal in shape ; the base of the pyramid is applied to the shaft 

 and directed downward and inward ; the apex rises nearly as high 

 as the head of the femur, and points outward, upward, and forward. 

 The trochanter is sharply defined in front from the shaft by a somewhat 

 irregular elevated line, which runs obliquely outward and downward 



