EXTENSOR PROPRIUS HALLUCIS 387 



3IUSCLES OF THE FRONT OF THE LEG 



Between the anterior border of the tibia and the anterior of the two external 

 intermuscular septa, are placed four muscles: the tibialis anticus, the extensor 

 proprius hallucis, the extensor longus digitorum, and the peroneus tertius. 



1. TIBIALIS ANTICUS 



The tibialis anticus — named from its attachment to the tibia and its position 

 in the front of the leg — is fusiform and somewhat flattened, Avith a long terminal 

 tendon. 



Origin. — (1) Part of the under surface of the outer tuberosity of the tibia; (2) 

 the outer surface of the upper two-thirds of the til)ia; (3) the adjacent part of the 

 anterior surface of the interosseous membrane; (4) the posterior surface of the 

 upper part of the deep fascia of the leg; (5) an intermuscular septum which sepa- 

 rates it from the extensor longus digitorum in the upper third of the leg. 



Insertion. — The lower part of the front of the inner surface of the internal 

 cuneiform Ijone and the adjacent part of the base of the first metatarsal bone. 



Structure. — A strong penniform muscle the fibres of Avhich, arising fleshy 

 from the bone and the fascia?, pass forwards and most of them somewhat 

 outwards to be attached to the deep surface and outer border of a tendon, which, 

 beginning below the middle of the leg, becomes free of fleshy fibres two or three 

 inches (5 to 8 cm.) above the ankle-joint; and, after passing first Iseneath the 

 upper portion of the anterior annular ligament, then partly under and partly over 

 the lower portion, expands slightly to be inserted upon the inner margin of the 

 foot. In passing over the instep it turns upon itself so that its anterior surface 

 becomes below internal. 



Nerve- supply. — From the anterior tibial division of the external popliteal 

 nerve by branches which enter the upper third of the muscle upon the outer part 

 of its deep aspect. 



Action. — (1) To flex the ankle-joint; (2) to draw upwards the inner border of 

 the foot and so invert the sole; (3) to adduct the front portion of the foot. The 

 first of these movements will be performed chiefly at the ankle-joint; the second 

 and third at the medio-tarsal and calcaneo-astragaloid joints. This muscle is of 

 great importance in walking, as it raises the anterior part of the foot and so 

 enables the toes to clear the ground when the leg is swinging forwards to begin 

 anotlier step. 



Relations.— Superficially, the deep fascia; on the outer side, the extensor 

 longus digitorum and extensor pr()i)rius hallucis with the anterior tibial vessels and 

 nerve; deeply, the interosseous mem])rane and the tibia. The tendon lies in a 

 special synovial sheath beneath tlie two portions of the anterior annidar ligament, 

 and upon the ankle-joint and inner bones of the tarsus. A small l)ursa separates 

 the tendon from the upper part of the inner surface of the internal cuneiform bone. 



Variations. — A small tendon is sonietimos sent to the head of the first metatarsal bone, the 

 base of the first phalanx of the great toe, or to the fascia covering the instep. 



2. EXTENSOR PROPRIUS HALLUCIS 



The extensor proprius hallucis — named from its being the special extensor 

 belonging to the great toe { proprin-^ = peculiar to) — is a somewhat triangular sheet. 



Origin. — (1) The middle two-fourths of the anterior (nr extensor) surface of the 

 fibula external to the attachment of the interosseous membrane; (2) the adjacent 

 portion of the anterior surface of the interosseous membrane. 



Insertion. — (1) The ligamentous structures at the back and sides of the first 



