The Lower Extremity and Pelvis 167 



Flexor Longus Hallucis. In a general way, remembering that the area of origin is 

 modified by the extent of Tibialis posticus, this muscle may be said to arise from the 

 posterior surface of the shaft in the middle third and from its internal aspect in the 

 lower third. The upper limit is recognised by the existence of roughnesses, caused by 

 its uppermost aponeurotic fibres ; the rest of its origin is by muscle fibre, as inspection 

 of the bone demonstrates, and its lower limit is a little above the level of the lower tibio- 

 fibular articulation. 



Observe that its upper part is prolonged up for a little distance between the Soleus 

 and Tibialis posticus, and indications of this can frequently be found on the bone, 

 although it is often obscured by the markings of tendinous fibres in the muscles. 



Soleus area extends down from the head on the back of the bone for its upper third : 

 its lower end is outside the upper part of the origin of the last muscle and is indicated 

 by rough markings, which may also be found in the higher part of the area. There 

 is a slight twist in the upper part of the bone, that causes the surface for this muscle 

 to look very slightly outwards as well as backwards and makes the muscle prominent 

 externally in its upper part. 



Peronei. The muscle areas are as shown in Fig. 137 : the upper one reaches the 

 tibio-fibular ligaments above and passes along them to the tibia. There are not usually 

 any indications on the bone of the distinct areas, although there are frequently slight 

 roughnesses for short tendinous fibres in the muscles. Notice that the divisions of the 

 external popliteal nerve lie in the substance of the upper muscle, practically on the bone, 

 and the musculo-cutaneous nerve comes forward between the two muscles, being 

 separated from the bone by Peroneus brevis. 



Extensor longus digitorum and Peroneus tertius arise from the narrow anterior 

 surface, from the ligamentous markings at the upper end to a point easily seen about 

 an inch above the anterior prominence of the lower end. The two muscles have a 

 continuous origin, the division made between them being purely an artificial one. They 

 occupy the whole of the anterior surface, except in the middle two-fourths, where 

 Extensor longus hallucis arises from the surface between them and the interosseous line. 

 Above the origin of this muscle the attachment of the long extensor of the digits is 

 interrupted by the passage of the anterior tibial nerve. 



The Extensors and Peronei are divisions of one mass of muscle tissue, the dorsal extensors 

 of the foot. At an early stage they are included in the same cellular layer (representing enclosing 

 fasciae), but are separated later by the growth of the outer malleolus. Thus the enclosing layer 

 is stranded on the surface of the subcutaneous area and covers it with a thick, felted fibrous 

 membrane. 



The anterior and posterior peroneal septa are attached respectively to the anterior 

 and posterior margins of the shaft, following the peroneal muscles closely. 



The deep transverse fascia of the leg separates the Soleus from the deep flexors 

 and main vessels and nerves. Its attachment has already been followed on the tibia 

 (p. 164) up to the fibrous arch over the vessels : from this it passes to the inner side 

 of the head of the fibula and runs down (Fig. 137), separating the Soleus at first from 

 Tibialis posticus, but then passing obliquely across the back of the bone to cover the 

 Flexor longus hallucis, and thus separating Soleus from this muscle. This oblique 

 line may occasionally be made out on the bone, but it is obscured as a rule by the fusion 

 of the fascia with the aponeurotic fibres of the muscles between which it passes. 



At the outer side of the long flexor the fascia blends with the posterior peroneal 

 septum, and the two are attached together to the postero-external edge as far as the 

 lower end, where they separate again to follow their respective muscle groups (Fig. 137). 



