The Lower Extremity and Pelvis 165 



Fibula. 



Observe that the styloid process is placed behind and outside the articular surface 

 on the head, and that the rough markings round the articular facet show the presence 

 of areas of ligamentous attachment ; these markings are best developed in front of 

 the styloid process, extending here on to the outer side of the head and showing the 

 insertion of the external lateral ligament, while round the other borders of the facet 

 they are made by the capsular ligamentous fibres of the tibio-fibular joint. 



The extent of attachment of the external lateral ligament and of the Biceps tendon 

 that covers it is seen in Fig. 137. Peroneus longus, arising from the outer side of the 

 upper part of the shaft, extends on to the lateral ligament as well as across the anterior 

 tibio-fibular bands to reach the tibia (Fig. 133), and the Biceps tendon gives an 

 aponeurotic expansion over this muscle as well as over the extensors. 



Soleus arises from the back surface of the upper part of the shaft and from the 

 back of the head as far up as the base of the process : on its inner side here there is a 

 tubercle which marks the attachment of the fibrous arch along which the origin of the 

 muscle passes from the tibia. 



On the inner side the ligamentous markings come lower down than on the other 

 margins of the facet, and below these, on the inner side of the neck, the bone is in 

 relation with the anterior tibial artery passing outwards, forwards and downwards 

 above Tibialis posticus. 



The Extensor longus digitorum arises from the neck in front of this arterial region, 

 its origin running up to the ligamentous area where it passes, with the Peroneus longus, 

 across to the tibia. 



The shaft of the bone has the appearance of being twisted in its length through a 

 quarter-turn in an outward direction : this is due to the disposition of the muscles 

 on it, for the bone is moulded in its shape by the muscles applied to it, and its margins 

 mark the attachment of strong fibrous septa between these muscles, so that, to under- 

 stand the arrangement of surfaces and lines on it, it is necessary to consider the 

 structures that produce them. 



First find the interosseous border. The inner aspect of the bone can be recognised at once 

 by the presence of articular facets on it, and there is a triangular rough area, above the lower facet 

 for the astragalus, that is made by the fibres of the interosseous ligament. This ligament is really 

 an ill-defined thickening of the lower end of the interosseous membrane, so that the line of the 

 membrane can be immediately found as a ridge leading up from the rough area (Fig. 137). Trace this 

 up, and it is seen to divide into two : the anterior line is the proper continuation of the interosseous 

 border, the posterior and more salient ridge being for the aponeurosis covering Tibialis posticus. 



The interosseous line can be followed up to the neck of the bone, and it divides 

 the inner aspect of the shaft into extensor and flexor regions : the extensors of the foot 

 lie immediately in front of it, and therefore occupy the area, variable in breadth but 

 never very wide, which lies between the interosseous line and the front border, while the 

 flexors of the foot lie behind it. Of these flexors the deepest is the Tibialis posticus, 

 which arises from the membrane and from the bones on each side of the membrane, 

 so that its area of origin on the fibula lies immediately behind the interosseous line : 

 it is bounded behind by the prominent postero-internal border and extends up to the 

 neck of the bone, including, within its limits, the oblique line or lines made by the 

 intramuscular tendons in the substance of the muscle (Fig. 137). The aponeurosis 

 covering Tibialis posticus affords origin to the next layer of muscles, the long flexors of 

 the toes. Flexor longus hallucis is very much stronger than Flexor longus dig., so that 

 the outer part of the aponeurosis is much thicker and stronger than the inner part, and 



