632 DISSECTION OF THE LEG. 



b. The metatarsal branch takes an arched course to the outer part of 

 the foot, near the base of the metatarsal bones and beneath the extensor 

 muscle, and anastomoses with the external plantar and tarsal arteries. 



c. From the arch of the metatarsal branch three dorsal interosseous 

 arteries are furnished to the three outer metatarsal spaces ; and the exter- 

 nal of these sends a branch to the outer side of the little toe. They sup- 

 ply the interossei muscles and divide at the cleft of the toes into two small 

 dorsal digital branches. 



At the fore part of the metatarsal space each interosseous branch joins 

 a digital artery in the sole of the foot by means of the anterior per- 

 forating twig ; and from the beginning of each a small branch, posterior 

 perforating, descends to the plantar arch. 



d. The first interosseous branch (art. dorsalis pollicis) arises from the 

 trunk of the artery as this is about to leave the dorsum of the foot ; it ex- 

 tends forwards in the space between the first two toes, and is distributed 

 by dorsal digital pieces like the other dorsal interosseous offsets. 



The ANTERIOR TIBIAL VEINS have the same extent and connections as 

 the vessel they accompany. They take their usual position along the 

 artery, one on each side, and form loops around it by cross branches ; they 

 end in the popliteal vein. The branches they receive correspond with 

 those of the artery ; and they communicate with the internal saphenous 

 vein. 



Dissection. To examine the extensor brevis digitorum on the dorsum of 

 the foot, cut through the tendons of the extensor longus and peroneus ter- 

 tius below the annular ligament, and throw them towards the toes. The 

 hinder attachment of the muscle to the os calcis is to be defined. 



The EXTENSOR BREVIS DIGITORUM arises from the outer surface of the 

 os calcis in front of the sheath for the peroneus brevis muscle, and from 

 the lower band of the anterior annular ligament. At the back of the meta- 

 tarsal bones the muscle ends in four tendons, which spring from as many 

 fleshy bellies, and are inserted into the four inner toes. The tendon of the 

 great toe has a distinct attachment to the base of the metatarsal phalanx ; 

 but the rest are united to the outer side of the long extensor tendons, and 

 assist to form the expansion on the metatarsal phalanx (p. 629). 



The muscle lies on the tarsus, and is partly concealed by the tendons of 

 the long extensor. Its inner belly crosses the dorsal artery of the foot. 



Action. Assisting the long extensor, it straightens the four inner toes, 

 separating slightly from each other. 



Dissection. The branches of artery and nerve \vhich are beneath the 

 extensor brevis will le laid bare by dividing that muscle near its front, 

 and turning it upwards. 



By cutting through the lower band of the annular ligament over the 

 tendon of the extensor pollicis, and throwing outwards the external half 

 of it, the different sheaths of the ligament, the attachment to the os 

 calcis, and the origin of the extensor brevis digitorum from it may be ob- 

 served. 



The anterior tibial and musculo-cutaneous nerves are now to be followed 

 upwards to their origin from the external popliteal : and a small branch to 

 the knee-joint from the same source is to be traced through the tibialis 

 anticus. 



NERVES TO THE FRONT OF THE LEG. Between the fibula and the pero- 

 neus longus muscle the external popliteal nerve divides into recurrent 

 articular, musculo-cutaneous, and anterior tibial branches. 



