BONES. 



anterior fossa is the larger and wider ; the posterior is concave 

 transversely and slopes downward and backward. The exter- 

 nal tubjerosity is the smaller but overhangs the shaft more ; the 

 facet for the fibula lies on the under surface of its most pro- 

 jecting part postero-externally ; the impression for the ilio- 

 tibial band is antero-external. The Semimembranosus tendon 

 grooves the circumference of the internal tuberosity postero- 

 internally. An oval elevation (tubercle of the tibia, or anterior 

 tuberosity) lies in front of the tuberosities, an inch below the 

 condyles; its upper half is smooth but the lower half is rough, 

 for the ligamentum patella?. [231] 



Shaft. This has three surfaces and three borders. The an- 

 terior border (crest, or shin) is curved and prominent; from 

 the tubercle it runs downward in front to the lower third and 

 then, fading away, toward the anterior border of the internal 

 malleolus. The internal border descends, from the internal tu- 

 berosity, to the posterior border of the internal malleolus ; it is 

 sharp at its midpart only. The external border (crista inter- 

 ossea) is a vertical ridge which descends, from the external tu- 

 berosity, to within two inches of the lower extremity and then 

 divides into two lines enclosing a triangular articular area. 

 The internal (subcutaneous) surface extends to the internal 

 tuberosity above, and becomes continuous with the inner sur- 

 face of the inner malleolus below. The external surface turns 

 forward, inferiorly, onto the front of the shaft. The posterior 

 surface is crossed above by a ridge (oblique, or popliteal line) 

 which runs downward and inward, from the fibular facet, to 

 the internal border at the junction of the upper and middle 

 thirds ; a vertical ridge descends from about the middle of the 

 popliteal line and divides this surface into inner and outer 

 parts. [233] 



Inferior Extremity. This is expanded and quadrangular. 

 On its under surface is a saddle-shaped facet, concave antero- 

 posteriorly and slightly convex transversely, with sharp an- 

 terior and posterior borders; the anterior border is often 



F2531 



