THE FIBULA 189 



surface is convex and covered by the extensor tendons and the anterior tibial 

 vessels. The posterior surface is limited by the interosseous crest and the medial 

 border. The upper part is crossed obliquely by a rough popliteal line, extending 

 from the fibular facet on the lateral condyle to the medial border, a little above the 

 middle of the bone. 



The popliteal line gives origin to the soleus and attachment to the popliteal fascia, while 

 the triangular surface above is occupied by the popliteus muscle. Descending along the 

 posterior surface from near the middle of the popliteal line is a vertical ridge, well marked at 

 its commencement, but gradually becoming indistinct below. The portion of the surface 

 between the ridge and the medialborder gives origin to the flexor digitorum longus; the lateral 

 and narrower part, between the ridge and the interosseous border, to fibres of the tibialis 

 posterior. The lower third of the posterior surface is covered by flexor tendons and the posterior 

 tibial vessels. Immediately below the popliteal line and near the interosseous border is the large 

 medullary foramen directed obliquely downward. 



The lower extremity, much smaller than the upper, is quadrilateral in shape 

 and presents a strong process called the medial malleolus, projecting downward 

 from its medial side. The anterior surface of the lower extremity is smooth and 

 rounded above, where it is covered by the extensor tendons, rough and depressed 

 below for the attachment of the anterior ligament of the ankle-joint. It some- 

 times bears a facet for articulation with the neck of the talus (astragalus). (A. 

 Thomson.) The posterior surface is rough and is marked by two grooves. The 

 medial and deeper of the two encroaches on the malleolus, and receives the tendons 

 of the tibialis 'posterior and flexor digitorum longus; the lateral, very shallow and 

 sometimes indistinct, is for the tendon of i\\e flexor hallucis longus. The lateral sur- 

 face is triangular and hollowed for the reception of the lower end of the fibula and 

 rough for the interosseous ligament which unites the two bones, except near the 

 lower border, where there is usually a narrow surface, elongated from before back- 

 ward, covered with cartilage in the recent state for articulation with the fibula. 

 The lines in front of and behind the triangular surface afford attachment to the 

 anterior and posterior ligaments of the inferior tibio-fibular articulation. The 

 medial surface, prolonged downward on the medial malleolus, is rough, convex, 

 and subcutaneous. The lateral surface of this process is smooth and articulates 

 with the facet on the medial side of the talus (astragalus). Its lower border is 

 notched, and from the notch, as well as from the tip and anterior border, the fibres 

 of the deltoid ligament of the ankle-joint descend. The inferior or terminal 

 surface, by which the tibia articulates -svith the talus, is of quadrilateral form, 

 concave from before backward, wider in front than behind, and laterally than 

 medially where it is continuous with the lateral surface of the malleolus. 



The occasional facet on the anterior surface of the lower extremity of the tibia is a pressure 

 facet, produced by extreme flexion of the ankle joint. It is therefore sometimes designated as 

 the "squatting facet." (See fig. 333.) 



Blood-supply. — The tibia is a very vascular bone. The nutrient artery of the shaft is 

 furnished by the posterior tibial, and is the largest of its kind in the body. The head of the 

 bone receives numerous branches from the inferior articular arteries of the popliteal and the 

 recurrent branches of the anterior and posterior tibial. The lower extremity receives twigs 

 from the posterior and anterior tibial, the peroneal, and the medial malleolar arteries. 



Ossification. — The tibia is ossified from one principal centre for the shaft, which appears 

 in the eighth week of intra-uterine life, and two epiphyses, the centres for which appear m the 

 cartilaginous head of the bone toward the end of the ninth month, and in the lower extremity 

 during the second year. The latter unites with the shaft at eighteen, but the union of the head 

 with the shaft does not take place until the twenty-first year, and it may even be delayed until 

 twenty-five. The upper part of the tubercle of the tibia is ossified from the upper epiphysis, 

 and the lower part from the diaphysis. 



THE FIBULA 



The fibula (figs. 224, 225) is situated on the lateral side of the leg and, in 

 proportion to its length is the most slender of all the long bones. It is placed 

 nearly parallel to the tibia with which it is connected above and below. In man 

 it is a rudimentary bone and bears none of the weight of the trunk, but is retained 

 on account of the muscles to which it gives origin and its participation in the 

 formation of the ankle-joint. Like other long bones, it is divisible into a shaft 

 and two extremities. 



The head [capitulum fibula], or upper extremity, is a rounded prominence. 

 Its upper surface presents laterally a rough eminence for the attachment of the 



