356 HUMAN ANATOMY. 



prominence of the linea aspera at the back. The surface on either side of this line 

 may be plane, concave, or convex, perhaps more often concave. The shaft expands 

 slightly above, where it is roughly four-sided with rounded borders. A ridge, which 

 is very variously developed, often runs from the lower side of the neck, separating 

 the anterior and internal surfaces. When strong, it emphasizes the concavity of the 

 former. The lower third of the shaft broadens. 



The linea aspera' is a prominent longitudinal ridge along the back of the 

 middle third of the bone, strengthening the concavity and giving attachment to 

 many muscles. It has two more or less well-defined borders or lips. It is formed 

 from above by the union of three lines : the spiral, a faint intermediate line coming 

 down from the lesser trochanter, and a third external one coming from the back of 

 the greater trochanter. The upper part of the last is called the gluteal ridge, as it 

 receives fibres of the gluteus maximus. This part may be considerably elevated, 

 especially in muscular subjects, into a rough knob, the spurious third trochanter. 

 The true third trochanter, which is sometimes seen at this point, is a smooth rounded 

 eminence, the analogue of the third trochanter extensively found among mammals 

 and particularly developed in the odd-toed ungulata. This is sometimes best 

 developed on delicate female femurs with no rough muscular ridges. Of course the 

 two forms may coexist. A rough elongated depression, \S\q fossa hypotrocha7iterica, 

 also receiving fibres of the gluteus, is sometimes found outside the gluteal ridge. 

 The linea aspera divides somewhat below the middle of the bone into two supra- 

 condylar ridges, which bound a triangular space ^ as they pass down to the tops 

 of the condyles. The outer ridge is at first much the sharper, but it becomes indis- 

 tinct an inch or more above the condyle. The inner is but slightly raised ; it is 

 interrupted above its middle for the passage of the femoral vessels into the popliteal 

 space. It ends in the sharp adductor tubercle above the inner border of the condyle. 

 At its termination the shaft has four surfaces : a posterior one nearly plane, a front 

 one slightly convex, a distinct outer one, and an oblique inner one, passing insensibly 

 backward and inward from the anterior surface. There are usually two nutrient 

 foramifia, both directed upward, the larger between the lines converging to the 

 linea aspera, the other near the middle of the bone, a little to the inside of that line. 



The lower extremity, articulating with the tibia below and the patella in 

 front, presents two backward prolongations, the condyles, along which the tibia 

 travels in fiexion. These are compressed from side to side, and separated by the 

 interco7idylar fossa ^ which is beneath the back part of the shaft. The iyiner condyle*' 

 is the lower when the shaft is vertical, but in life both are in the same plane. The 

 outer" is longer from before backward ; it lies in an antero-posterior plane, while the 

 inner extends backward and inward. The lateral outline of each has been well com- 

 pared to a watch-spring partly uncoiled. Each bears a tuberosity near the posterior 

 end of the lateral side, very nearly in continuation with the supracondylar ridges 

 for the so-called lateral ligaments of the knee. A depression on each side for the 

 head of the gastrocnemius is found above and behind the tuberosities. The ex- 

 ternal condyle bears a deep oblique groove for the tendon of the popliteus at the 

 back of the outer surface. 



The articular surface for the knee not only covers the lower and posterior 

 aspects of the condyles, but is prolonged upward on the front for the support of the 

 patella, as a groove which is shown by horizontal sections to be concave in the 

 middle and convex at either side. The upper boundary slants upward and outward, 

 the shaft just above it presenting a slight depression. Its outer border is a promi- 

 nent ridge resisting outward dislocation of the knee-pan. The patellar surface is 

 continuous with the articular facets of the condyles, being marked of? only by certain 

 lines, which, though distinct on the fresh cartilage, are often obscure on the dried 

 bone, representing the separation of these joints. In some animals the separation is 

 complete. The 02iter litie, usually concave posteriorly, runs obliquely inward to 

 just in front of the intercondylar notch. The inner, less clear and generally straight, 

 begins much farther forward and runs obliquely backward to the inner side of the 

 front of the notch. The outer in particular marks a distinct change of level. Be- 

 hind these lines the articular surfaces extend along the lower and posterior sides of 

 the condyles even onto the upper aspect, so as to allow extreme flexion of the knee, 



' Linea aspera. ^ Planum popliteum. ^ Fossa inlercondyloidea. ''Condylus medialis. ^ Condylus lateralis. 



