THE ANTERIOR TIBIO-FIBULAR REGION. 435 



and nerve in the upper part of the leg. By its inner surface, with the tibia ; by- 

 its outer surface, with the Extensor longus digitorum and Extensor proprius hal- 

 lucis, and the anterior tibial vessels and nerve. 



The Extensor proprius hallucis is a thin, elongated, and flattened muscle situ- 

 ated between the Tibialis anticus and Extensor longus digitorum. It arises from 

 the anterior surface of the fibula for about the middle two-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 downward, and 

 terminate in a tendon which occupies the anterior border of the muscle, passes 

 through a distinct compartment in the lower portion of 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. It usually sends an expansion from the inner side of the 

 tendon, to be inserted into the base of the first phalanx. 



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

 ment; by its posterior surface, with the interosseous membrane, fibula, tibia, and 

 ankle-joint ; by its outer side, with the Extensor longus digitorum above, the dorsalis 

 pedis vessels, anterior tibial nerve, and Extensor brevis digitorum below ; by its 

 inner side, with the Tibialis anticus and the anterior tibial vessels above. The 

 muscle is external to the anterior tibial vessels in the upper part of the leg ; but 

 in the lower third its tendon crosses over them, so that it lies internal to them on 

 the dorsum of the foot. 



The Extensor longus digitorum is an elongated, flattened, penniform muscle 

 situated the most externally of all the muscles on the fore part 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 ; 

 from the deep surface of the fascia ; and from the intermuscular septa between it 

 and the Tibialis anticus on the inner and the Peronei on the outer side. The 

 tendon enters a canal in the annular ligament with the Peroneus tertius, and divides 

 into four slips, which run across the dorsum of the foot and are inserted into the 

 second and third phalanges of the four lesser toes. The mode in which the tendons 

 are inserted is the following : The three inner tendons opposite the metatarso- 

 phalangeal articulation are joined, on their outer side, by a tendon of the Extensor 

 brevis digitorum. They all receive a fibrous expansion from the Interossei and 

 Lumbricales, and then spread out 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 onward, to be inserted into 

 the base of the third. 



Relations. By its anterior surface, with the fascia and the annular ligament ; 

 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 hallucis, and anterior tibial vessels and nerve ; by its outer side, with the 

 Peroneus longus and 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, from the lower part of the 

 interosseous membrane, and from an intermuscular septum between it 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 dorsal 

 surface of the base of the metatarsal bone of the little toe. This muscle is some- 

 times wanting. 



Nerves. These muscles are supplied by the fourth and fifth lumbar and first 

 sacral nerves through the anterior tibial nerve. 



Actions. The Tibialis anticus and Peroneus tertius are the direct flexors of the 



