The area is well defined by the interosseous line and posterointernal border except at the top, where the two structures which make the lines are continuous as thin fasciae that usually leave no marking on the bone : the area is not limited in any way by the oblique lines, which are included in it, being the attachments of intramusailar tendons.
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 tibiofibular 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.