THE CRURAL MUSCLES. 647 



Nancrede says, that of the six popHteal bursae, one — the subpopliteal {d) — 

 always communicates with the joint, and occasionally with the upper tibio-fibular 

 joint (Gruber) ; one — that between the gastrocnemius and the semimembranosus 

 (a) — generally does so ; and one {c) occasionally does so. 



Enlargement of these bursae leads to stiffness and disability in the use of the 

 knee. Extension may be painful and may show the presence of a tense, rounded, 

 fluctuating swelling. This will usually be at the inner side of the popliteal region, 

 because the bursa beneath the gastrocnemius and semimembranosus — the largest of 

 the bursae — is the one most often enlarged. 



It may, on account of the transmitted pulsation, be mistaken for an aneurism, 

 but should be distinguished by the facts that, if due to bursal enlargement, the swell- 

 ing — unlike that of aneurism — may (a) lessen or quite disappear when the knee is 

 slightly flexed, the narrow passage between the bursal sac and the joint being com- 

 pressed when the posterior ligament is tense and patulous when it is relaxed ; {b~) 

 reappear slowly and not almost instantly ; {c) become tenser and more prominent on 

 full extension ; (</) will have a transmitted, not an expansile pulsation; and ((?) 

 will be unaffected as to bulk by digital compression of the femoral artery. 



A popliteal lipoma — the only other condition likely to be confused with a non- 

 suppurating, enlarged bursa — occupies no definite position in the ham, has no sharply 

 defined outline, undergoes little or no increase of tension when the leg is extended, 

 and is apt to have attachments to the deep surface of the skin (Nancrede). 



THE CRURAL MUSCLES. 



The crural muscles are primarily inserted into the bones of the leg or into the 

 tarsus, but, like the antibrachial muscles, many of them have been extended into 

 the foot and act upon the digits. 



The crural fascia is a strong aponeurotic sheath investing the muscles of the 

 leg, at the knee being continuous with the fascia lata and below with the fascia of 

 the foot. Over the e eternal and internal malleoli and along the entire inner surface 

 of the tibia the fascia blends with the subjacent periosteum ; from the last of these 

 attachme'nts a deep layer is given off which passes across to the fibula, between the 

 superficial and deeper muscles of the back of the leg. That portion of the fascia 

 which covers the muscles of the front of the leg is exceedingly strong, but it is 

 thinner over the calf. The upper part of its posterior portion is somewhat thickened, 

 and forms part of the roof of the popliteal space. Below the fascia is strengthened 

 bv transverse fibres which form bands that bind down the tendons passing over the 

 ankle-joint. 



Of these bands two are situated upon the anterior surface of the ankle-joint, 

 together forming the structure termed the anterior annular ligament (Fig. 623). 

 The upper or vertical portion of this (ligamentum transversum cruris) extends trans- 

 versely across between the lower ends of the tibia and fibula, a little above the ankle- 

 joint. The space beneath this band is divided by a partition into two compartments, 

 the more lateral of which contains the extensor longus hallucis and the extensor 

 longus digitorum, enclosed by separate synovial sheaths, while the more medial one 

 contains the tibialis anticus. The lower or horizontal portion oi the ligament (liga- 

 mentum cruciatum) is Y-shaped. Externally it is attached to the outer surface of 

 the calcaneum and passes inward, enclosing the tendons of the extensor longus digi- 

 torum, and then divides into two limbs, the upper of which passes upward and 

 inward, over the tendons of the extensor longus hallucis and the tibialis anticus, to 

 be inserted into the inner malleolus, just below the medial end of the ligamentum 

 transversum. The lower limb passes downward and inward to be attached to the 

 inner border of the plantar fascia. 



On the posterior surface three bands occur. Two of these serve to bind down 

 the tendons of the peroneus longus and brevis as they pass behind the external mal- 

 leolus, together forming the lateral annular ligament fretinacula mm. peroaaeorum). 

 The upper band extends downward and backward from the outer malleolus to the 

 calcaneum, while the lower one, arising from the calcaneum at the point at which 

 the outer end of the cruciate ligament is attached, extends backward over the 



