420 MUSCLES AND FASCIA. 



fourths of its extent, its origin being internal to that of the Extensor Longus 

 Digitorum; it also arises from the interosseous membrane to a similar extent. 

 The fibres pass downwards, and terminate in a tendon, which occupies the an- 

 terior border of the muscle, passes through a distinct compartment in the 

 annular ligament, crosses the anterior tibial vessels near the bend of the ankle, 

 and is inserted into the base of the last phalanx of the great toe. Opposite the 

 metatarso-phalangeal articulation, the tendon gives off a thin prolongation on 

 each side, which covers the surface of the joint. 



Relations. By its anterior border, with the deep fascia, and the anterior annular 

 ligament. By its posterior border, with the interosseous membrane, fibula, tibia, 

 ankle-joint, and Extensor Brevis Digitorum. By its outer side, with the Exten- 

 sor Longus Digitorum above, the dorsalis pedis vessels and anterior tibial 

 nerve below. By its inner side, with the Tibialis Anticus and the anterior tibial 

 vessels above. 



The Extensor Longus Digitorum is an elongated, flattened, semipenniform 

 muscle, situated the most externally of all the muscles on the forepart of the 

 leg. It arises from the outer tuberosity of the tibia ; from the upper three- 

 fourths of the anterior surface of the shaft of the fibula ; from the interosseous 

 membrane, and deep fascia ; and from the intermuscular septa between it and 

 the Tibialis Anticus on the inner, and the Peronei on the outer side. The 

 muscle terminates in three tendons, which pass through a canal in the annular 

 ligament, with the Peroneus Tertius, run across the dorsum of the foot, and are 

 inserted into the second and third phalanges of the four lesser toes, the inner- 

 most tendon having subdivided into two. The mode in which the tendons are 

 inserted is the following: Each tendon opposite the metatarso-phalangeal articu- 

 lation is joined, on its outer side, by the tendon of the Extensor Brevis Digi- 

 torum (except the fourth), and receives a fibrous expansion from the Interossei 

 and Lumbricales ; it then spreads into a broad aponeurosis, which covers the 

 dorsal surface of the first phalanx. This aponeurosis, at the articulation of the 

 first with the second phalanx, divides into three slips, a middle one, which is 

 inserted into the base of the second phalanx ; and two lateral slips, which, after 

 uniting on the dorsal surface of the second phalanx, are continued onwards, to 

 be inserted into the base of the third. 



Relations. By its anterior surface, with the deep fascia and- the annular liga- 

 ment. By its posterior surface, with the fibula, interosseous membrane, ankle- 

 joint, and Extensor Brevis Digitorum. By its inner side, with the Tibialis 

 Anticus, Extensor Proprius Pollicis, and anterior tibial vessels and nerve. By 

 its outer side, with the Peroneus Longus and Peroneus Brevis. 



The Peroneus Tertius is a part of the Extensor Longus Digitorum, and might 

 be described as its fifth tendon. The fibres belonging to this tendon arise from 

 the lower fourth of the anterior surface of the fibula, on its outer side ; from 

 the lower part of the interosseous membrane; and from an intermuscular septum 

 between the Peroneus Tertius and the Peroneus Brevis. The tendon, after 

 passing through the same canal in the annular ligament as the Extensor Longus 

 Digitorum, is inserted into the base of the metatarsal bone of the little toe, on 

 its dorsal surface. This muscle is sometimes wanting. 



Nerves. These muscles are supplied by the anterior tibial nerve. 



Actions. The Tibialis Anticus and Peroneus Tertius are the direct flexors of 

 the tarsus upon the leg ; the former muscle, from the obliquity in the direction 

 of its tendon, raises the inner border of the foot ; and the latter, acting with 

 the Peroneus Brevis and Peroneus Longus, will draw the outer border of the 

 foot upwards, and the sole outwards. The Extensor Longus Digitorum and 

 Extensor Proprius Pollicis extend the phalanges of the toes, and, continuing 

 their action, flex the tarsus upon the leg. Taking their fixed point from below, 

 in the erect posture, all these muscles serve to fix the bones of the leg in the 

 perpendicular position, and give increased strength to the ankle-joint. 



