592 A MANUAL OF ANATOMY. 



Extensor Brevis Digitorum. Fig. 124. 



Origin. From the outer and upper surface of the fore 

 part of the os calcis, from the external calcaneo-astragaloid 

 ligament, and from the lower band of the anterior annular 

 ligament. 



Insertion. By four tendons. The first tendon is inserted 

 into the outer surface of the base of the first phalanx of the 

 great toe ; the rest of the tendons merge into the outer 

 margins of the tendons of the extensor longus digitorum 

 (just over the bases of the first phalanges), and by them 

 are attached to the second and third phalanges. 



Nerve Supply. The anterior tibial. 



Action. To extend and adduct (toward the middle line 

 of the second toe) the first phalanx of the great toe, to ex- 

 tend the third, second, and first phalanges of the next three 

 toes. The action of the muscle upon the toes is more upon 

 the distal than the proximal segments of them. 



Dorsal Interossei. Fig. 125. 



There are four dorsal interossei muscles. There is one 

 on either side of the second toe ; then the third and fourth 

 toes have each a muscle upon their outer (fibular) side. 



Origin. From the adjacent sides of the metatarsal bones 

 between which they lie. Between the two heads pass the 

 posterior perforating arteries. (In the case of the first mus- 

 cle it is the communicating artery.) 



Insertion. Into the bases of the first phalanges, and into 

 the lateral margins of the tendons of the extensor longus 

 digitorum ; upon the inner side of the second toe for the 

 first muscle, and upon the outer side of the second, third, 

 and fourth toes for the remaining muscles. 



Nerve Supply. The external plantar branch of the pos- 

 terior tibial nerve. 





