518 MESSRS. M1VART AND CLARKE ON THE SACRAL 



which we were indebted to the great kindness of Professor Flower, and to Professor 

 Parker for the other. We found both sides to agree as to the arrangement of the roots 

 of the lumbar and sacral plexus, and at the same time to differ from the description 

 above taken from Hoffman, as also from that given by Gegenbaur as existing in Lizards 

 generally. "We found the sacral plexus and sciatic nerves to be formed by four roots, 

 the most postaxial of which comes from the first postsacral nerve. "We found the lumbar 

 plexus to be formed by three roots, the most preaxial of which is the fourth presacral 

 nerve. Fibres from all the roots of the lumbar plexus appear to go to form the obtu- 

 rator nerve ; but the crural nerve seems to be formed from the second and third presacral 

 nerves only. 



The main difference between our specimens and the figure and descriptions of the 

 authors referred to, however, consists in the concurrence of the first postsacral nerve in 

 the formation of the sacral plexus. 



In order the better to determine the essential nature of the nerve-roots, we thought it 

 desirable to follow out their branches to the muscles which are supplied by them ; being 

 favoured by the large size and fine condition of the specimens examined. 



The fifth presacral nerve (1) we found to have no connexion with the lumbar plexus, 

 but to send its branches to the pyramidalis 1 and other abdominal muscles. 



The fourth presacral nerve (2) bifurcated, the more preaxial branch (3) going to the 

 internal oblique 2 and perhaps other abdominal muscles. The postaxial bifurcation (4) 

 went to form the obturator nerve, but sometimes, before doing so, gave off a branch (7) to 

 the iliacus z . The muscle is, however, also supplied by branches given off (7) from the 

 obturator nerve itself, as on one side of the specimen figured. 



The third presacral nerve (9) joins a branch (11) from the second presacral nerve, and 

 it may communicate with the last-mentioned nerve by an additional short nervous 

 connexion (14). 



The second presacral nerve (11 + 12) bifurcates, the preaxial bifurcation (11) joining 

 the third presacral nerve, with or without the aid of the short connecting branch (14). 

 Either at this junction (13), or from the second presacral nerve before the junction, the 

 crural nerve (15) is given off. The postaxial bifurcation joins the sacral plexus. The 

 second and third presacral nerves having thus joined together, they are continued on 

 by a single branch (10) which joins the postaxial bifurcation (4) of the fourth sacral 

 nerve, before described, to form the obturator nerve (5), which, after giving off a branch 

 (6) to the iliacus, perforates the pubic foramen and then divides into branches, which 

 respectively go to the pectineus, obturator externus, tibial adductor, adductor magnus, and 

 gracilis muscles. 



The crural nerve (starting, as has been said, either directly from the preaxial bifur- 

 cation of the second presacral nerve, or else from the junction of this bifurcation with the 

 third presacral) passes over the brim of the pelvis, and, giving off two or three branches 



1 In naming the muscles, we have followed the nomenclature adopted in the paper " On the Myology of Iguana 

 tuberculata," published in the ' Proceedings of the Zoological Society ' for 1867, p. 766. The pyramidalis is there 

 described at p. 772. 



s This muscle is described at p. 771 of the paper referred to. 3 For iliacus see I. e. p. 787. 



