174 THE SALAMANDER 



dorsalis pedis fibularis (n.d.p.f.)- The N. dors. ped. fib. — the post-axial 

 branch — almost immediately divides again and gives off a branch 

 which passes along the leg between it and the N. dors. ped. inter. It 

 innervates the M. extensor digitorum communis (e.d.) and MM. 

 extensores breves digitorum 3 and 4 (e.b.3 and e.b.4) and sends a 

 large branch to join the N. dors. ped. inter. This ramus is not men- 

 tioned by Sieglbaur. It is named here R. accessorius n. dorsalis pedis 

 fibularis (n.d.p.f.). 



A comparison with the fore-limb suggests that the essential 

 difference between it and the hind-limb is that in the former case 

 the anterior and posterior extensor nerves remain separate until dis- 

 tal to the elbow-joint, so that the extensor communis muscle and the 

 ulnar extensor muscles are innervated by sundry twigs from both the 

 N. ext. caudalis, and from the N. dors. man. ulnaris — a branch from 

 the N. ext. cranialis. In the hind-limb, however, the anterior and 

 posterior extensor nerves of the thigh unite proximal to the knee to 

 form a single trunk which redivides in the leg, so that the extensor 

 communis muscle and the fibular extensors are innervated by the 

 N. dors. ped. fib. and its R. accessorius, which separate from the N. 

 dors. ped. inter, as a single bundle. A comparison of Plates XI and 

 XII will make this clear. 



The N. dorsalis pedis fibularis (n.d.p.f.), after separating from the 

 R. accessorius, passes down the leg along the extensor side of the 

 fibula, immediately deep to the M. extensor cruris et tarsi fibularis. 

 It innervates this muscle by several twigs (e.c.t.f.). At about the 

 level of the distal end of the fibula it receives an anastomosis from 

 the R. accessorius, while at the distal edge of the M. extensor cruris 

 et tarsi fibularis it gives off a cutaneous branch to the skin of the 

 post-axial side of the fifth digit — N. digitalis dorsalis 5. The remain- 

 der of the nerve crosses the base of this toe, giving a muscular twig 

 to the M. ext. brev'. digit. 5, and then divides to supply the adjoining 

 sides of digits 4 and ^—NN. digitales dorsales 4 and 5. 



N. dorsalis pedis intermedius (n.d.p.i.). This comparatively large 

 nerve passes along the interosseal space of the tibia and fibula 

 to the tarsus. It lies immediately posterior to the N. interosseus, and 

 during this part of its course it innervates the tibial extensor muscles, 

 viz. M. extensor tarsi tibialis (e.t.t.), and M. extensor cruris 

 tibialis, the latter twigs coming off" near the origin of the nerve. At 

 the ankle it gives twigs to the M. abductor et extensor digiti i 

 (a.e.i), and to the MM. ext. breves digitorum of the second digit 

 (e.b.2). The nerve then divides into two, one branch — the anterior — 

 supplying the adjoining sides of digits 2 and 3 — NN. digitales dors. 



