REPORT ON THE MARSUPIALIA. 143 



endo-gluteus, and supplies filaments to both. In Cuscus a long slender twig can be traced 

 downwards to end in the ecto-gluteus, where it folds round the lower margin of the 

 meso-gluteus to become continuous with the endo-gluteus. The fibres to which this twig 

 is distributed undoubtedly represent the tensor fascise femoris. 



Small sciatic. — In the Thylacine (PI. IV. fig. 5, s.s.n) this is a purely cutaneous nerve, 

 whilst in the Cuscus (PI. III. fig. 1, s.s.n) it also contains motor fibres which it dispenses 

 to the ecto-gluteus. Emerging from the pelvis through the great sacro-sciatic foramen 

 in front of the pyriformis it makes its entrance into the gluteal region under cover of the 

 meso-gluteus. It soon appears at the posterior border of this muscle, and then proceeds 

 backwards upon the pyriformis and ischio-femoral muscles covered by the ecto-gluteus. 

 Finally, dipping under the superficial vertebral origin of the biceps muscle it becomes 

 superficial on the back of the thigh, and is distributed to the skin as low down as the 

 upper part of the leg. 



Nerve to hamstrings (PI. III. fig. 1, h.n, and PI. IV. fig. 5, h.n). — This is hardly an 

 appropriate name for this nerve, seeing that it has a much wider distribution than to the 

 hamstring muscles, but it is difficult to suggest a better. It is a large nerve, composed 

 entirely of motor fibres. It enters the gluteal region through the great sacro-sciatic 

 foramen, and proceeds backwards upon the endo-gluteus, and under cover of the pyri- 

 formis. At the lower border of the latter muscle it gives off a large branch (PI. III. 

 fig. 1, g.n) — the representative of the nerve to the quadratus femoris in man, — and then 

 continues downwards under the ischio-femoral muscle to the under surface of the biceps 

 muscle. Here it breaks up into a large number of branches for the supply of the biceps 

 and its various accessory parts, the semitendinosus and the semi-membranosus. 



In the Cuscxis the nerve to the quadratus femoris sinks into the substance of the 

 gemelli muscles, and is continued backwards through their muscular fibres. Issuing from 

 the midst of the gemellus inferior, it is carried downwards under cover of the quadratus 

 femoris to the adductor magnus. In this course it supplies twigs to the gemelli, quadratus 

 femoris, and probably to the obturatus internus, whilst it ends in the adductor magnus, 

 and constitutes its sole nerve of supply. 



In the Thylacine the distribution of the nerve to the quadratus is precisely similar 

 to that in the Cuscus, but its relations to the gemelli muscles are somewhat different. Each 

 gemellus consists of a superficial and deep part, and the nerve in passing backwards passes 

 between the two portions of the superior muscle, and then under cover of the obturator 

 internus and both portions of the inferior gemellus. 



In Thylacinus and Cuscus, therefore, the adductor magnus is associated by its nervous 

 supply with the quadratus femoris, and it draws branches from neither of its usual 

 sources, viz., the great sciatic and the obturator nerves. The advocates for the theory 

 that nerve-supply points infallibly to the homology of a muscle will find this a difficult 

 fact to solve. Of course it might be explained by supposing that the adductor mao-nus 



