i8o THE NERVOUS SYSTEM 



The Peronceus Brevis has a similar origin, but it passes above the 

 trochlear process and is inserted into the tubercle on the base of the fifth 

 metatarsal bone. Both these muscles act as plantar flexors of the foot, 

 but, at the same time, they elevate the lateral border of the foot from the 

 ground, i.e. they act as powerful evertors. When they are brought into 

 action, a distinct furrow is produced on the lateral aspect of the leg and, 

 hi the bottom of this furrow, the contracted muscular bellies can be felt. 

 The tendons also can be palpated as they cross the lateral aspect of the 

 calcaneus (os calcis), just distal to the lateral malleolus. 



The Deep Peroneal Nerve enters the anterior compartment 

 of the leg and is, at first, very deeply placed. As it descends, 

 it supplies branches to the neighbouring muscles and, opposite 

 the ankle-joint, it divides into lateral and medial branches, 

 which extend on to the dorsum of the foot. The lateral 

 branch is mainly distributed to the extensor digitorum brevis, 

 but the medial branch runs forwards to supply the contiguous 

 sides of the hallux and second toe. 



The Tibialis Anterior forms the muscular prominence in the proximal 

 part of the anterior compartment of the leg. It arises from the tibia and 

 its tendon passes distally and medially, crossing the anterior aspect of the 

 ankle-joint, to be inserted into the base of the first metatarsal and the medial 

 cuneiform bone. The tibialis anterior acts as a powerful dorsi-flexor and, 

 in company with the tibialis posterior, as a powerful inverter of the foot. 



The Extensor Hallucis Longus and the Extensor Digitorum Longus 

 arise from the fibula and pass distally in front of the ankle-joint. The 

 former is inserted into the base of the terminal phalanx of the hallux, and 

 the latter divides into four tendons, which are inserted into the lateral four 

 toes in the same manner as the tendons of the extensor digitorum com- 

 munis in the fingers. 



Both these muscles dorsi-flex the foot in addition to extending the toes. 



The Peronceus Tertius arises from the distal part of the fibula and its 

 fleshy belly is continuous with that of the extensor digitorum longus. It 

 crosses the anterior aspect of the ankle-joint and is inserted into the dorsum 

 of the base of the fifth metatarsal bone. Its principal action is to assist in 

 dorsi-flexion of the foot, but it also helps in the movement of eversion. 



The Extensor Digitorum Brevis is a small muscle, which arises from the 

 anterior part of the upper surface of the calcaneus (os calcis). When the 

 toes are strongly extended, it forms a small elevation, a little in front of 

 the lateral malleolus. It gives origin to four tendons, which pass to the 

 medial four digits. 



