144 THE VOYAGE OF H.M.S. CHALLENGER. 



is a compound muscle, consisting of a part belonging to the adductor group, which in this 

 case has fused with the large adductor brevis, and a part derived from the flexor group, 

 which in the present instance is independent, and receives its nerve fibres from the same 

 source, but through a different nerve-strand, viz., the nerve to the quadratus. 



The adducting group of muscles holds an intermediate position in the thigh, and in 

 Man it seems to merge in front with the extensors, and behind with the flexors. The 

 nerve supply points to this. Thus the pectineus is furnished with twigs from the 

 obturator and anterior crural nerves, whilst the adductor magnus is supplied by the 

 obturator and great sciatic nerves. 



Pudic (PL III. fig. 1, p.n, and PL IV. fig. 5, p.n). — This is a small nerve which runs 

 backwards under cover of the pyriforrnis muscle, and then through the small sciatic 

 notch to the perineum. In the gluteal region of the Thylacine it gives a small twig to 

 the posterior of the two vertebral portions of the biceps, whilst in Cuscus it receives 

 a communicating twig from the nerve to the hamstrings (PL V. fig. 6, p). 



Great sciatic (PL III. fig. 1, and PL IV. fig. 5, g.s.n). — The great sciatic enters the 

 gluteal region under cover of the meso-gluteus, and proceeds backwards upon the pyri- 

 forrnis, obturator internus and gemelli, and the ischio-femoral muscle, to the under 

 surface of the biceps. Half-way down the thigh it ends by dividing in three, viz.: — (1) 

 internal popliteal ; (2) external popliteal ; (3) external saphenous. It gives off no 

 collateral branches. 



External saphenous (PL V. fig. 2, 1). — This large nerve proceeds downwards under 

 cover of the biceps to the outer back aspect of the leg, along which it runs to the external 

 maleolus. It is continued behind this bony prominence to the outer margin of the pes, 

 where it ends as the fibular dorsal collateral branch of the little toe (PL VI. fig. 8, 1). 

 It supplies (a) muscular, (b) communicating, and (c) cutaneous twigs. 



The muscular branches are different in the two animals. In TJn/lacinus it sends a 

 twig to the lower part of the biceps. In Cuscus it gives a branch to the inner head 

 of the gastrocnemius, and another to the fibular part of the vertebral portion of the 

 1 deeps. 



The communicating branches are — (1) a strongly marked twig, present in both animals, 

 which passes inwards under cover of the tendo-Achillis and the tendon of the plantaris to 

 join the external plantar nerve (PL V. fig. 2, 2); (2) in the Cuscus a twig to the musculo- 

 cutaneous nerve on the dorsum of the foot (PL VI. fig. 8). 



The cutaneous twigs are very numerous, and supply the skin over the outer aspect of 

 the leer and foot. 



Internal popliteal (PL VI. fig. 8, 4). — This is the largest of the three terminal divisions 

 of the great sciatic. In Thylacinus it sends off behind the knee joint, and between the 

 heads of the gastrocnemius a large number of muscular branches to the superficial and 

 deep muscles on the back of the leg, and then divides into the external and internal 



