104 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



Between the condylar parts is an interval which is depressed 

 in front and behind for attachment of crucial ligaments, and 

 elevated in the middle, forming the spine, the summit of which 

 presents two compressed tubercles with an intervening hollow. 

 The depression behind the spine is continued into the popliteal 

 notch, which separates the tuberosities posteriorly. Anteriorly, 

 at the junction of the head and shaft, is the tubercle or anterior 

 tuberosity, the lower half of which gives attachment to the 

 ligamentum patellae. 



The shaft is three-sided, diminishing in size as it descends 

 for about two-thirds of its length, and then increasing again. 

 It presents three borders and three surfaces. 



The anterior border runs sinuously from the tubercle to the 

 front of the inner malleolus; its upper two-thirds is the crest of 

 the tibia; its lower third is smooth. It separates the internal 

 and external surfaces. 



The internal border, which is most distinct in the middle 

 third of the bone, commences above at the back part of the 

 inner tuberosity, ending below at the posterior border of the 

 internal malleolus. It separates the internal and posterior 

 surfaces. 



The external border, or interosseous ridge, is thin and sharp 

 in its middle portion. It separates the external and posterior 

 surfaces, and gives attachment to the interosseous membrane. 



The internal surface is convex and nearly subcutaneous. 

 At the inner side of the tubercle are the insertions of the gracilis, 

 semitendinosus, and double insertion of the sartorius. The 

 external surface is hollowed in its upper two-thirds, where it 

 lodges the tibialis anticus; below this the surface runs forward 

 and is covered by the extensor tendons. The upper third 

 of the posterior surface is crossed obliquely by the popliteal 

 or oblique line, running down and inward; it gives origin to 

 the soleus. Above it is a triangular area occupied by the 

 popliteus; below it, in the middle third of the shaft, is a longi- 

 tudinal ridge marking off two portions, an inner for the flexor 

 longus digitorum, and an outer for the tibialis posticus. Below 

 the oblique line a large medullary canal runs downward. 



The inferior extremity is broad from side to side, and pro- 

 jects downward internally to form the inner malleolus. This 

 malleolus is marked posteriorly by a groove for the tibialis 

 posticus tendon, and more externally by a depression for the 



