Variation* in Spi/naZ Nerves of Hyla wu/rea. 281 



cent., being the only form having those thicknesses of nerve 

 VIII. On comparing this with Fig. 1, form iii. (to which the 

 Table C, iii. refers), we find that the ileo-hypogastric originates 

 entirely from nerve VIII., the remainder of which passes down 

 and unites with a branch from IX. to form the cruralis, that is 

 to say, the region supplied by the ileo-hypogastric, is controlled 

 by nerve VIII. only. On the other hand the most primitive 

 form, according to the percentages, should be form i., which only 

 occurs with the smallest thickness of nerve VIII. Fig. 1, form i.) 

 shows that in this the most primitive condition, nerve VIII. 

 takes absolutely no share in the formation of the ileo-hypogastric 

 nerve, this as well as the cruralis being supplied by nerve IX. 

 only. Between these two forms, i., the most primitive, and iii., 

 the most advanced, we have as an intermediate stage form ii., in 

 which we find VIII. and IX. taking an equal share in forming 

 the ileo-hypogastric. The cruralis is variously formed when this 

 is the case, four per cent, of such cases having the position and 

 relations shown by the continuous lines only, and sixty per cent, 

 that shown by both continuous and dotted lines. I have not 

 separated these two forms in the table, as there are but very few 

 observations, and also I shall discuss the progression of the crural 

 nerve in detail later on. 



It will thus be seen that whereas the ileo-hypogastric in its 

 more primitive condition originates from nerve IX., as it 

 advances, it tends more and more to become connected with 

 nerve VIII. , until in the great majority of the present forms it 

 is only connected with that nerve, thus showing a transference 

 of function forwards, i.e., from IX. to VIII. 



A further instance of this was noted in one specimen in which 

 the ileo-hypogastric branch of VIII. received a branch — tine, 

 certainly — from VII. It would thus appear that there is now 

 a tendency for VII. to be drawn into the sacral plexus, and 

 possibly it will, later on, take part in the formation of the crural 

 nerve also, progressing in just the same way as VIII. has done, 

 as may be seen from Figs. 1, 2 and 3. Of this, however, one can 

 only speak with reserve, inasmuch as it only occurred in one 

 specimen, and then not in conjunction with any of the greater 

 thicknesses of VII. or VIII. (VII. having thickness 3, and 

 VIII. thickness 5). Table C shows that by far the most 



