530 THE MUSCLES AND FASCIA 



1. Dorsal Region. 



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. 330) is a broad thin muscle which arises 

 from the fore part of the upper and outer surfaces of the os calcis, in front of the 

 groove for the Peroneus brevis, from the external calcaneo-astragaloid 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 dorsal surface of the base of 

 the first phalanx of the great toe, crossing the Dorsalis pedis artery ; 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 hallucis;'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 first phalanges of all four inner toes. The obliquity of its direc- 

 tion 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 Region. 



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 betAveen the two former groups. But in order 

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

 divide them into four layers, as they present themselves, in the order in which 

 they are successively exposed. 



First Layer. 



Abductor hallucis. 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 backward. The central portion should be divided trans- 

 versely in the middle of the foot, and the two flaps dissected forward and backward. 



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

 the inner tubercle on the under surface of the os calcis ; from the internal annular 

 ligament ; from the plantar fascia ; and from the intermuscular septum between it 

 and the Flexor brevis digitorum. The fibres terminate in a tendon which is 

 inserted, together with the innermost tendon of the Flexor brevis hallucis, into 

 the inner side of the base of the first phalanx of the great toe. 



Relations. By its superficial surface, Avith the plantar fascia ; by its deep sur- 

 face, with the Flexor brevis hallucis, the Flexor acccssorius, and the tendons of 

 the Flexor longus digitorum and Flexor longus hallucis, the Tibialis anticus and 

 posticus, the plantar vessels and nerves, and the articulations of the tarsus. 



The Flexor brevis digitorum (perforatus) lies in the middle of the sole of the 

 foot, immediately beneath 1 the plantar fascia, with which it is firmly united. It 

 1 That is, in order of dissection of the sole of the foot. 



