PELVIC LIMBS 729 



entire proximal surface, but more often is separated by a notch from 

 the posterior angle, which is produced for ligamentous attachment. 



The Shaft of the fibula is very slender, and difficult to describe. 

 It is flattened from side to side, and at first sight appears to consist 

 of two surfaces, an external and an internal, separated by two 

 borders, an anterior and a posterior. A closer examination, however, 

 reveals on strongly developed bones four borders, three Avell marked 

 and one obscurely defined, which limit four surfaces. 



The borders may be named the anterior-internal, the anterior- 

 external, the posterior-external, the posterior-internal, and the surfaces 

 the anterior, the external, the posterior, and the internal. 



The anterior-internal border (Figs. 552, 555) is easily recognized 

 as a sharp edge facing inward and forward. It is opposite the ex- 

 ternal border of the tibia, to which it is joined by the strong inter- 

 osseous membrane ; hence it is also known as the interosseous 

 ridge. It begins above as the continuation of the anterior-inferior 

 border of the head, runs vertically for a short distance, and then 

 turns inward, becomes sharper and more prominent, and ends by 

 bifurcating above the inferior extremity. The anterior branch of 

 this division is continued straight down as the anterior border of 

 the inferior extremity, and the posterior branch turns backward to 

 form the posterior boundary of its anterior-external surface. The 

 anterior-internal border separates the anterior from the posterior and 

 internal surfaces. 



The anterior-external border begins in common with the anterior- 

 internal border and runs straight down to the lower third, where it 

 gradually turns backward, approaches the posterior-external border, 

 and fades out at a point proximal to the inferior extremity. It is 

 never sharp nor prominent, and in some bones appears rather as the 

 line of anterior maximum convexity than as a distinct border. It 

 separates the anterior and external surfaces. 



The posterior-external border (Fig. 554) is well marked. It 

 begins above from the outer side of the lower end of the eminence 

 on the back of the posterior-external surface of the head, and passes 

 straight downward ; it curves somewhat inward at the middle of the 

 leg, and ends as the inner boundary of the posterior-external surface 

 of the inferior extremity. This border is rounded above, but becomes 

 sharp in the lower third. It separates the external and posterior 



