1338 HUMAN ANATOMY. 



down the front of the leg as far as the ankle, lying first to their outer side, then 

 anterior to them and at the ankle to the outer side again (Fig. iii6j. 



Branches of the anterior tibial nerve are : (aa) the nuiscular, {^bb) the articular, 

 i^cc) the external and {dd) internal ternimal. 



aa. The muscular branches are distributed to the tibiaHs anticus, the extensor longus 

 digitorum, the extensor proprius hallucis and the peroneus tertius. 



The nerves to the tibialis anticus consist of two twigs, an upper and a lower. The upper 

 arises at the origin of the anterior tibial, passes beneath the peroneus longus and tire extensor 

 longus digitorum and enters the upper portion of the muscle. The lower arises in the interval 

 between the tibialis anticus and the extensor longus digitorum and passes obliquely downward 

 into the substance of the tibialis anticus. 



The nerve to the extensor longus digitorum arises immediately below the preceding and 

 enters the inner surface of the muscle which it supplies. 



The nerves to the extensor proprius hallucis, usually two in number, arise in the middle of 

 the leg and enter the substance of their muscle. 



The nerve to the peroneus tertius is usually derived from the nerve to the extensor 

 longus digitorum. 



bb. The articular branch leaves the anterior tibial above the anterior annular ligament and 

 is distributed to the forepart of the ankle-joint. 



cc. The internal terminal branch (Fig. 1117) courses forward in the foot under the inner 

 tendon of the extensor brevis digitorum and lateral to the dorsalis pedis artery, and reaches 

 the base of the first digital cleft. Here it splits into two branches (nn. digitales dorsales hallucis 

 lateralis et digiti secundi medialis), which supply the contiguous sides of the great and second 

 toes and inosculate with branches of the musculo-cutaneous nerve. In the region of the tarsus 

 it sends off \\\^ first dorsal interosseous nerve, which supplies the first dorsal interosseous muscle, 

 the mesial metacarpal articulations and the first and second metacarpo-phalangeal joints. Like 

 the other interosseous nerves, it sends a filament between the heads of its dorsal interosseous 

 muscle for the supply of the adjacent articulations (Ruge). 



dd. The external terminal branch (Fig. 11 18) passes laterally over the tarsus under cover 

 of the extensor brevis digitorum, to which muscle it sends branches. From it are given off two 

 to four, usually three, dorsal interosseous branches, which decrease in size from within outward, 

 the fourth often being lacking and the third quite rudimentary. These interosseous nerves are 

 distributed to the adjacent articulations and sometimes to the second and third dorsal inter- 

 osseous muscles. The fibres from the anterior tibial to the dorsal interosseous muscles are 

 usually not their sole supply, the external plantar supplying constant branches for their innerva- 

 tion. From the latter are probably derived the motor iimervation and from the occasional ante- 

 rior tibial branches some extra sensory filaments. This branch usually ends in a gangliform 

 enlargement, from which its branches are distributed. 



Variations. — The anterior tibial sometimes supplies the mesial side of the great toe or the 

 adjacent sides of the second and third toes. In one case the anterior tibial supplied the outer 

 three and one-half toes, the inner toe and one-half being innervated by the musculo-cutaneous 

 nerve. Rarely the anterior tibial has no digital distribution whatsoever. 



c. The Musculo-Cutaneous Nerve. 



The musculo-cutaneous nerve (n. peronaeus superficialis) (Fig. 11 16) continues 

 the course and direction of the external popliteal. Descending through the leg in a 

 fascial tube in the septum between the peroneal muscles and the e.xtensor longus 

 digitorum it becomes superficial by piercing the deep fascia anterior to the fibula in 

 the lower third of the leg. It may make its superficial appearance as a single nerve 

 or as two branches. 



Branches of the musculo-cutaneous are: (aa) the vmsciilar, (^bb) the mternal 

 and (<rr) the external terminal. 



aa. The muscular branches (rr. musculares) are destined for the peronei longus and 

 brevis. 



The nerves to \hQ peroneus longus are two in number, an upper and a lower. They are 

 given off at the upper and lower portions respectively of the fascial canal occupied by the parent 

 nerve and enter the mesial surface of their muscle. 



The nerve to the peroneus brevis arises with the lower branch to the peroneus longus and 

 enters the musculature of the peroneus brevis. 



