184 



THE SKELETON 



the medial head of the gastrocnemius on the upper aspect of the condyle ; below 

 and behind the lateral epicondyle is a deep groove which receives the tendon of 

 the popliteiis muscle when the knee is flexed, and its anterior end terminates in 

 a pit from which the tendon takes origin. Above the lateral epicondyle is a 

 rough impression for the lateral head of the gastrocnemius. 



The interior of the shaft of the femur is hollowed out by a large medullary canal, and the 

 extremities are composed of cancellated tissue invested by a thin compact layer. The arrange- 

 ment of the cancelli in the upper end of the bone forms a good illustration of the effect produced 

 bj'' the mechanical conditions to which bones are subject. In the upper end of the bone the 

 cancellous tissue is arranged in divergent curves. One system springs from the lower part of 

 the neck and upper end of the shaft medially and spreads into the great trochanter (' pressure 

 lamellae'). A second system springs from the lateral part of the shaft and arches upward into 

 the neck and head ('tension lamella^'), crossing the former almost at right angles. 'A second set 

 of pressure lamellse springs from the lower thick wall of the neck, and extends into the upper 

 part of the head to end perpendicularly in the articular surface mainly along the lines of greatest 

 pressure. A nearly vertical plate of compact tissue (calcar femorale) projects into the neck 

 of the bone from the inferior cervical tubercle toward the great trochanter. This is placed in 

 the line through which the weight of the body falls, and adds to the stability of the neck of the 

 bone; it is said to be liable to absorption in old age. In the lower end of the bone the vertical 

 and horizontal fibres are so disposed as to form a rectangular meshwork. 



Blood-supply. — The head and neck of the femur receive branches from the inferior gluteal, 

 obturator, and circumflex arteries, and the trochanters from the circumflex arteries. The 

 nutrient vessel of the shaft is derived from either the second or third perforating artery, or 

 there may be two nutrient vessels arising usually from the first and third perforating. The 

 vessels of the inferior extremity arise from the articular branches of the popliteal and the 

 anastomotic branch of the femoral (supremagenu). 



Ossification. — The femur is ossified from one primary centre for the shaft and from four 

 epiphysial centres. The shaft begins to ossify in the seventh week of intra-uterine life. Early 

 in the ninth month a nucleus appears for the lower extremity. During the first year the nucleus 

 for the head of the bone is visible, and in the fourth year that for the trochanter majtor. The 

 centre for the lesser trochanter appears about the thirteenth or fourteenth year. The lesser 

 trochanter joins the shaft at the seventeenth, the great trochanter at the eighteenth, the head 

 about the nineteenth, and the lower extremity at the twentieth year. 



The neck of the femur is an apophysis, or outgrowth from the shaft. The line of fusion of 

 the condylar epiphysis with the shaft passes through the adductor tubercle. 



The morphological relation of the patellar facet to the tibial portions of the condyles is 

 worthy of notice. In a few mammals, such as the ox, this facet remains separated from the 

 condyles by a furrow of rough bone. 



The angle which the neck of the femur forms with the shaft at birth measures, on an average, 

 160°. In the adult it varies from 110° to 140°; hence the angle decreases greatly during the 

 period of growth. When once growth is completed, the angle, as a rule, remains fixed. 

 (Humphry.) 



THE PATELLA 



The patella (fig. 222) or knee-pan, situated in front of the knee-joint, is a sesa- 

 moid bone, triangular in shape, developed in the tendon of the quadriceps femoris. 

 Its anterior surface, marked by numerous longitudinal striae, is slightly convex, and 



Fig. 222.— The Left Patella 



Anterior surface 



Posterior surface 

 Lateral articular facet 



perforated by small openings which transmit nutrient vessels to the interior of the 

 bone. It is covered in the recent state by a few fibres prolonged from the com- 

 mon tendon of insertion (supra-patcliar tendon) of the quadriceps femoris, into the 

 ligamcntum patella? (infra-patellar tendon), and is separated from the skin by one 



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