268 Proceedings of the Royal Society of Victoria. 



cutaneus abdominalis, which pierces the Obliquus interims muscle 

 on its way to the skin, and the Ramus muscularis, supplying the 

 abdominal muscles. The rest of the VIII. fibres pass backward 

 to join the sacral plexus. Nerves IX. 'and X. are thick, IX. 

 being generally the thicker of the two. The crural nerve 

 generally consists of fibres from VIII. and IX. in almost equal 

 proportions, and may contain fibres from X. or not, according as 

 X. joins IX. above or below the origin of the Cruralis. 

 Occasionally the crural nerve may consist chiefly of IX. fibres 

 with a very small branch from VIII., or more seldom of chiefly 

 VIII. fibres with very few from IX. Very rarely, the crural 

 nerve may be composed of IX. fibres only, the whole of VIII. 

 then forming the ileo-hypogastric, or more often, the cruralis 

 consists of VIII. fibres only, in which case VIII. sends down also 

 a branch to enter the sciatic nerve. As in Rana, the crural nerve 

 runs out to the thigh and there lies upon the Ilio-psoas muscle 

 in an angle between the Adductor maguus, and the Rectus femoris 

 anticus. By far its larger branch, the Ramus cutaneus femoris 

 supplies the skin while other branches supply the Adductores 

 longus and bfevis, Ilio-psoas, Vastus inlernus, and sometimes the 

 Rectus femoris anticus and pectineus. From the fusion of IX. and 

 X. arises the sciatic nerve, which supplies all those parts of the 

 leg to which the cruralis does not send branches. It may or may 

 not contain any fibres from VIII. according to the manner in 

 which VIII. is connected with the sacral plexus, i.e., whether it 

 joins IX. above the origin of the crural from IX., or joins the 

 crural itself. 



The sciatic nerve most frequently consists of almost equal 

 quantities of IX. and X alone, though often VIII. fibres enters 

 into its composition and rather less frequently XL fibres, while 

 very rarely indeed X. forms the bulk of the sciatic, which then 

 also contains very few IX. fibres; or it may be chiefly IX., in 

 which case X. is a thin nerve, and VIII. fibres are always 

 present. The sciatic nerve runs backwards and enters the thigh 

 having almost the same relations as in Rana. While still in the 

 body it gives. off a branch — Ramus cutaneus femoris posterior — 

 which supplies the skin of the ventral and inner sides of the 

 thigh ; and also sends a twig to the Rectus internus minor. In 

 its course down the thigh, the sciatic sjives off several branches 



