350 MUSCLES AXD FASCIJE. 



tliick behind, thin in front, and extends from the os calcis forwards to the base of 

 the fifth metatarsal bone, into the outer side of which it is attached ; it is con- 

 tinuous internally with the middle portion of the plantar fascia, and externally 

 with the dorsal fascia. 



The inner portion is very thin, and covers the Abductor pollicis muscle ; it is 

 attached behind to the internal annular ligament, is continuous around the side 

 of the foot with the dorsal fascia, and externally with the middle portion of the 

 plantar fascia. 



MUSCLES OF THE FOOT. 



These are divided into two groups : 1. Those on the dorsum ; 2. Those on the 

 plantar surface. 



1. DORSAL KEGIOST. 

 Extensor Brevis Digitorum. 



The Fascia on the dorsum of the foot is a thin membranous layer, continuous 

 above with the anterior margin of the annular ligament ; it becomes gradually 

 lost opposite the heads of the metatarsal bones, and on each side blends with the 

 lateral portions of the plantar fascia. It forms a sheath for the tendons placed on 

 the dorsum of the foot. On the removal of this fascia, the muscles of the dorsal 

 region of the foot are exposed. 



The Extensor Brevis Digitorum is a broad thin muscle, which arises from the 

 outer side of the os calcis, in front of the groove for the Peroneus brevis ; from 

 the astragalo-calcanean ligament ; and from the horizontal portion of the anterior 

 annular ligament ; passing obliquely across the dorsum of the foot, it terminates 

 in four tendons. The innermost, which is the largest, is inserted into the first 

 phalanx of the great toe ; the other three, into the outer sides of the long Extensor 

 tendons of the second, third, and fourth toes. 



Relations. By its superficial surface, with the fascia of the foot, the tendons of 

 the Extensor longus digitorum, and Extensor proprius pollicis. By its deep sur- 

 face, with the tarsal and metatarsal bones, and the Dorsal interossei muscles. 



Nerves. It is supplied by the anterior tibial nerve. 



Actions. The Extensor brevis digitorum is an accessory to the long Extensor, 

 extending the phalanges of the four inner toes, but acting only on the first phalanx 

 of the great toe. The obliquity of its direction counteracts the oblique movement 

 given to the toes by the long Extensor, so that, both muscles acting together, the 

 toes are evenly extended. 



2. PLANTAR EEGION. ' 



The muscles in the plantar region of the foot may be divided into three groups, 

 in a similar manner to those in the hand. Those of the internal plantar region 

 are connected with the great toe, and correspond with those of the thumb ; those 

 of the external plantar region are connected with the little toe, and correspond 

 with those of the little finger ; and those of the middle plantar region are con- 

 nected with the tendons intervening between the two former groups. In order to 

 facilitate the dissection of these muscles, it will be found more convenient to divide 

 them into three layers, as they present themselves, in the order in which they are 

 successively exposed. 



First Layer. 



Abductor Pollicis. Flexor Brevis Digitorum. 



Abductor Minimi Digiti. 



Dissection. Remove the fascia on the inner and outer sides of the foot, commencing in front 

 over the tendons, and proceeding backwards. The central portion should be divided transversely 

 in the middle of the foot, and the two flaps dissected forwards and backwards. 



