PERONEUS LONGUS AND .; BREVIS, 261 



fibula, from the fascia of the leg, and from the intermuscular septum on each side. 

 The muscular fibres end in the lower half of the leg on a tendon which passes 

 downwards with that of the peroneus brevis in the , hollow behind the external 

 malleolus; it next inclines forwards on the outer side of the os calcis, and then 

 winds round the outer end of the tuberosity of the cuboid to enter the groove on 

 the lower surface of that bone ; finally, crossing the sole obliquely inwards and 

 forwards, it is inserted into an impression on the outer side of the tuberosity of the 

 first metatarsal bone, and slightly into the adjoining part of the internal cuneiform 

 bone : an offset is frequently sent from it to the base of the second metatarsal bone. 



Relations. At its origin the peroneus longus lies between the extensor longus digitorum in 

 front and the soleus and flexor longus hallucis behind ; in the lower part of the leg it lies behind 

 the peroneus brevis. Its attachment to the bone is interrupted for about an inch below the 

 head of the fibula, where the external popliteal nerve passes beneath it. Behind the external 

 malleolus the tendons of both peronei are contained in the same sheath under the annular 

 ligament, but on the outer side of the os calcis each tendon has its own sheath, the two being 

 separated by a fibrous septum and by the peroneal spine of the calcaneum. when that process 

 exists. A single synovial sac invests both tendons and sends two processes downwards into 

 the special sheaths. In the sole of the foot the tendon of the peroneus longus lies in a canal 

 formed by the cuboid bone and the long plantar ligament, and is surrounded by a second 

 synovial membrane. A sesamoid fibro-cartilage, or sometimes a bone, is found in that part of 

 the tendon which plays over the tuberosity of the cuboid. 



The peroneus brevis arises from the lower two- thirds of the external surface 

 of the fibula, extending upwards in front of the peroneus longus, and from the 

 intermuscular septum on each side. Its tendon passes down behind the external 

 malleolus, and then inclines forwards to be inserted into the tuberosity at the base 

 of the fifth metatarsal bone, sending in a majority of cases a small slip to join the 

 extensor tendon of the little toe, or to the fore part of the metatarsal bone. 



Relations. In front it is in contact with the extensor longus digitorum and the peroneus 

 tertius, and behind with the peroneus longus and flexor longus hallucis. The common 

 synovial membrane surrounds the tendon under the annular ligament, and sends a prolonga- 

 tion into its special sheath, above that for the peroneus longus. 



Varieties. Fusion of the two peronei is rare. A slip from the peroneus longus to the 

 base of the third, fourth or fifth metatarsal bone, or to the adductor obliquus hallucis is 

 occasionally seen. 



The peroneus aecewor'rug arises from the fibula between the peroneus longus and brevis, and 

 joins the tendon of the former in the sole of the foot. 



The peroneus qu'nitl diyiti arises from the lower fourth of the fibula under the peroneus 

 brevis, and is inserted into the extensor aponeurosis of the little toe ; this is rarely present as 

 a distinct muscle, but it is commonly (58 per cent. 1 ) represented by the above-mentioned slip 

 of the tendon of the peroneus brevis. It occurs normally in many animals, either as a separate 

 muscle, or united to a greater or less degree with the peroneus brevis. 



The pcronciift yuartus arises from the back of the fibula, between the peroneus brevis and 

 the flexor hallucis. and is inserted into the peroneal spine of the os calcis (peronco-calcancitit 

 exter tins') or less frequently into the tuberosity of the cuboid (peroneo-cuboideus). It was 

 found by Gruber in about 13 per cent. 



Nerves. The peroneus longus and brevis are supplied by the musculo-cutaneous "branch of 

 the external popliteal nerve. 



POSTERIOR REGION. 



The muscles at the back of the leg consist of a superficial group inserted into 

 the extremity of the calcaneum, and a deeper group covered in by a deep fascia and 

 for the most part descending to the sole. 



The SUPERFICIAL GROUP consists of three muscles ; two of them, the gastro- 

 cnemius and soleus, are of large size, form the bulk of the calf of the leg, and 



1 Gruber, " Beobachtungen," Heft vii, 1886; Cunningham and Brooks, Proc. Roy. Irish Acad., 



1887. 



s 2 



