1G6 THE VOYAGE OF H.M.S. CHALLENGER. 



the limb this nerve gives off a branch which passes transversely forwards between the 

 flexor perforatus and the inner head of the gastrocnemius. It terminates by supplying 

 branches to the anterior head of the gastrocnemius (23), and to the flexor perforans 

 digitorum (24). 



(e) The next branch derived from the sciatic nerve supplies the inner head of the 

 gastrocnemius (25), the flexor perforans digitorum (26), and the popUteus (27). 



Having given off these branches, the sciatic nerve divides into two parts, a large and 

 a small, both of which pass through the fibrous pulley of the biceps muscle. 



{f) The smaller of the two terminal branches (28), after passing through the fibrous 

 pulley of the biceps muscle, runs downwards along the outer side of the leg, under cover 

 of the superficial origin of the flexor perforatus as far as the ankle joint, where it breaks 

 up into branches for the supply of the skin covering the outer side of that articulation. 



In Apteiiodytes there are two cutaneous branches, which follow a similar course, and 

 are similarly distributed, except that the second one does not pass through the puUey of 

 the biceps. 



(g) The larger terminal branch of the sciatic nerve (29) also passes through the pulley 

 of the biceps muscle, and descending along the outer border of the fibula, under cover of the 

 peroneus longus and outer head of the gastrocnemius, as far as the ankle joint, gives off a 

 digital branch (30) to the outer side of the external toe. The nerve then passes down- 

 wards as far as the cleft of the toes, where it divides into two digital branches (31, 82) 

 for the supply of the contiguous sides of the middle and outer toes. It moreover gives a 

 twig to the sole of the foot, which passes through a foramen between the middle and outer 

 metatarsal bones. Immediately below the knee joint the main trunk gives off branches 

 of supply to the tibialis anticus (33), extensor longus digitorum (34), and peroneus longus 

 (3.5), and a branch of considerable size (36), which, winding round the outer side of the 

 fibula, reaches the front of the leg, where it lies in contact with the fibula, under cover 

 of the tibialis anticus, and supplies a branch to the peroneus brevis (37). Extending 

 downwards, this nerve passes along with the tendon of the tibialis anticus beneath the 

 anterior annular ligament, and reaching the cleft of the toes divides into two digital 

 branches (38, 39) for the supply of the contiguous sides of the middle and inner toes. It 

 moreover supplies a branch to the posterior or rudimental toe. 



The remaining lumbo-sacral nerves, namely, the ninth to the thirteenth inclusive, pass 

 obliquely backwards and outwards. The ninth, tenth, and eleventh run close together, 

 and terminate by supplying the lateral muscles of the tad and the skin in the neigh- 

 bourhood of the anus. From one of these nerves a branch is given to supply the cruro- 

 coccygeus muscle. The twelfth and thirteenth lumbo-sacral accompany the coccygeal 

 nerves, with which they are distributed. The thirteenth lumbo-sacral nerve passes out 

 between the first moveable coccygeal vertebra and the last bone of the lumbo-sacral mass. 



