484 THE MUSCULATURE 



Insertion. — Into the tip of the tuberosity of the fifth metatarsal. 



Nerve-supply. — The nerve arises from the superficial peroneal (musculo-cutaneous) nerve, 

 or from a branch to the peroneus longus. It enters the proximal margin of the muscle and 

 passes distally across its constituent fibre-bundles. 



Relations. — The peroneal muscles in the leg are contained in a compartment bounded by 

 the anterior and posterior intermuscular septa, by the fibula, and by the fascia of the leg. The 

 peroneus longus to a considerable degree overlies the peroneus brevis. Beneath the upper part 

 of the peroneus longus the peroneal (external popliteal) nerve bifurcates into its two chief 

 branches. The deep peroneal (anterior tibial) nerve passes medially beneath the anterior head 

 of the muscle. The superficial peroneal (musculo-cutaneous) nerve extends in the interval 

 between the areas of the attachment of the two heads of the peroneus longus, and along the an- 

 terior margin of the peroneus brevis to the anterior intermuscular septum, through which it 

 passes to its superficial distribution. The tendon of the peroneus longus at fu'st lies lateral to 

 and slightly overlaps that of the peroneus brevis. Toward the tip of the malleolus it lies almost 

 directly posterior to this tendon. On the lateral surface of the calcaneus the tendon of the 

 brevis lies superior to that of the longus, from which it is separated by a bony spine, the processus 

 trochlearis of the calcaneus. The tendon of the longus is separated from the deep surface of the 

 abductor of the little toe, and is held in place in the groove in the cuboid by the long plantar 

 ligament. 



Action. — The peroneus brevis everts the foot. The peroneus longus extends, abducts, and 

 everts the foot, and supports the arch of the foot. The peroneus brevis also extends the foot 

 when this is greatlj- flexed. 



Variations. — The two peroneal muscles may be more or less fused. The origin of the 

 peroneus longus may extend to the femur. The two heads of origin may be fused. Its tendon 

 of insertion may send slips to the second, third, and rarely to the fourth and fifth metatarsals. 

 The tendon may be united to that of the tibialis posterior (12 out of 45 bodies — Picou). Sesa- 

 moid cartilages or bones are occasionally found in the retro-malleolar and calcaneal portions of 

 the tendon. The tendon of the peroneus brevis may send a slip to the second or third phalanx 

 or to the head of the metatarsal of the fifth toe, to its extensor tendon, or to the cuboid. It may 

 also send a fasciculus to the fourth metatarsal or the extensor tendon of the fourth toe. 



Accessory peroneals. — Poirier considers these all varieties of a muscle which in its simplest 

 form arises from the distal fourth of the fibula and is inserted by a tendon into the fifth toe. A 

 corresponding muscle is normally found in many of the monkeys (peroneus digiti quinti). In 

 man in one form or another it is a frequent anomaly. It may be so fused with the peroneus 

 brevis that onlj' its tendon of insertion is appai-ent. It may appear as a special muscle fasciculus 

 of the peroneus longus or brevis. It may be merely a tendinous band, or it may be tendinous 

 at origin and insertion, with an intermediate belly. Instead of being attached to the fifth toe, 

 it may be inserted into the fifth metatarsal, the cuboid, the tendon of the peroneus longus, the 

 calcaneus, lateral malleolus, or posterior talo-fibular ligament. 



Synovial Tendon-sheaths 



Vagina tendinum peroneorum communis. — There is a double sheath for the tendons of 

 the peroneal muscles as they pass back of the lateral malleolus. From this region of union the 

 sheath sends processes along each tendon proximally above the malleolus and distally over the 

 lateral surface of the calcaneus. This process on the tendon of the peroneus longus often 

 communicates with the following sheath. Vagina tendinis m. peronaei longi plantaris. — ■ 

 This sheath begins in the peroneal groove of the cuboid and ends near the medial border of the 

 long plantar hgament. 



3. Musculature of the Back op the Leg 



a. Superficial Group (fig. 413) 



To this group belong the gastrocnemius, soleus, and plantaris muscles. They 

 extend the foot and flex the leg. The two ovoid heads of the gastrocnemius arise 

 one on each .side from above the condyles of the femur, extend about to the middle 

 of the back of the leg, and are inserted into the posterior surface of the tendon of 

 .Vchilles, and through this into the back of the calcaneus. The broad, flat, ovoid 

 soleus arises beneath the gastrocnemius from the tibia and fibula, and is in- 

 serted into the deep surface of the tendon of Achilles as far as the ankle. The 

 two heads of the gastrocnemius and the soleus constitute the triceps surae. The 

 plantaris is a slender muscle which passes along the medial margin of tlu; lateral 

 head of tin; gastrocnemius and beneath the medial head, where it gives rise to a 

 slender tendon that runs betw(um the gastrornKunius and soleus and along the 

 medial margin of Uu) t(!udon of Achilles to the fatty fibrous tissue of the heel. 

 The nerve-supply is from tin; tibial nerve. 



jThe muscles of this group have a common embryonic origin, and are first differentiated 

 on the fibular side of the leg, whence they extend over the i)bsterior til)ial vessels and nerve to 

 their medial attachments. The gastrocnemius corresponds with the flexor carpi radialis and 

 ulnari.s, tlie plantaris with the j)ahnaris longus, the soleus with a portion of the flexor digitorum 



