428 MUSCLES AND FASCIAE. 



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

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

 the side of the foot with the dorsal fascia, and externally with the middle por- 

 tion of the plantar fascia. 



MUSCLES OF THE FOOT. 

 These are found in two regions: 1. On the dorsum ; 2. On the plantar surface. 



1. DORSAL EEGION. 

 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 

 and tendons of the dorsal region of the foot are exposed. 



The Extensor Brevis Digitorum (Fig. 258) 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. It passes obliquely across the dorsum of the 

 foot, and 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 surface, 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 KEGION. 



The muscles in tjie 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 ; but in 

 order to facilitate the dissection of these muscles, it will be found more con- 

 venient to divide them into four 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. 



The Abductor Pollicis lies along the inner border of the foot. It arises from 

 the inner tuberosity on the under surface of the os calcis ; from the internal 

 annular ligament; from the plantar fascia; and from the intermuscular septum 



