Variations in Spinal Kef res of Hyla a urea. 293 



gastric preceding the cruralis because of its position nearer to 

 the spinal column. 



In Fig. 3 we find form ii. occurring with nerve VIII., thick- 

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

 XI., thickness 2 ; and form iii. with nerve III., thickness 3, 

 nerve IX., thickness 7, nerve X., thickness 7, and nerve XI., 

 thickness 1 — that is to say, as nerve VIII. increases, nerve 

 IX. increases, and nerve XI. decreases, thei*e is a decreasing 

 tendency for nerve XI. to take any share in the forma- 

 tion of the sciatic. There is, therefore, here again a 

 forward Homoeosis. Nerve X. would seem to offer a slight, 

 difficulty in this respect, due probably to the small number 

 of observations. 



In Fig. 4 we see again an evidence of this same forward 

 advance in the composition of the sciatic, and in the 

 l'elations of nerve XI. to the leg, since form i. occurs 

 with nerve XL, thickness 2, and form iii. with thickness 1 

 of nerve XI., nerve XL it will be remembered being in a 

 state of decrease. 



In Fig. 5, form ii. occurs with nerve III., thickness 6, and 

 nerve IV., thickness 3 ; and form iii., with nerve III., thickness 

 5, and nerve IV., thickness 6. Here we see that nerve III. 

 appears to oft'er a slight deviation from Hyla aurea, since it 

 decreases slightly in these few observations. On the other hand, 

 however, nerve IV. increases greatly and as it does so takes an 

 increasing share in the brachial plexus and therefore in the 

 innervation of the fore-limb. 



The results with reference to nerve II. are interesting. We 

 find that in Fig. 6, form ii., nerve II. has thickness 3, and in 

 form iii. it has thickness 4. If we premise, that as in Hyla aicrea y 

 II. is decreasing in thickness, then we have here, it would 

 appear, an increasing connection of II. with the brachial plexus; 

 but reference to Tables P and O will show that Fig. 6, form iii. 

 is a very unusu'al form in Hyla aurea, so that we cannot attach 

 much importance to this fact. 



In Limnodynastes tasmanieiisis we find the following thick- 

 nesses : — 



