Variations in Spinal Newes of Hyla av/rea. 295 



The ileo-hypogastric always shows its highest development, 

 Fig. 1, form iii. The craralis has reached the stage in which 

 it has only equal quantities of VIII. and IX. (cf. Fig. 2, 

 form v.) AVe tind Fig. 3, form iii., the sciatic heing composed 

 of IX. and X. fibres in equal quantities, with nerve VIII., 

 thickness 2, nerve IX., thickness 5, nerve X., thickness 6, and 

 nerve XL, thickness 2, and with the other thicknesses noted for 

 these nerves, we tind in addition to IX. and X. fibres, some of 

 VIII. Nerve XL is entirely absent from the sciatic, having 

 reached its highest development, Fig. 4, form iii. 



In the brachial plexus we find Fig. 5, form ii., with nerve IV., 

 thickness 3, and nerve III., thickness 5, and form iii., with nerve 

 IV., thickness 3, and nerve III., thickness 7. 



Thus with an increasing thickness of nerve III. we get an 

 increasing importance of IV. in the brachial plexus. Further 

 with an increasing thickness of nerve III. we have an increasing 

 connection of II. with this plexus, since with nerve III., thick- 

 ness, 7, we have Fig. 6, form ii., and Fig. 6, form iii., with nerve 

 III., thickness 5. 



In the specimen of Chiroleptes platycephalus from Central 

 Australia, which I examined, I found the following thicknesses : 

 Nerve II., thickness 3, nerve III., thickness 11, nerve IV., 

 Thickness 5, nerve V., thickness 3, nerve VI., thickness 2, nerve 

 VII., thickness 3, nerve VIII. , thickness 4, nerve IX., thickness 

 8, nerve X., thickness 5, nerve XL, thickness 2. The ileo-hypo- 



