PLEXUS AND SACRAL VERTEBRAE OF LIZARDS. 517 



Agama colonorum. (Plate LXVI. fig. 5.) 



This animal was the only one found, by us to present that character figured 1 by 

 Professor Gegenbaur, and described by him as existing in all Lizards 2 , namely, the non- 

 junction with the sacral plexus of the first postsacral nerve (30). The most postaxial of 

 the sciatic roots was the intersacral nerve (29), which gave off one or two branches (41), 

 going to the cloaca and tail respectively. The first presacral nerve (21) formed the 

 stoutest root ; but besides a rather stout lumbo-sacral nerve (12) (forming the postaxial 

 bifurcation of the second presacral) the sacral plexus also received a slender branch (46) 

 from the third presacral, which bifurcates at its origin like the second presacral. In 

 no other Lizard whatever have we found the sacral plexus receive a branch from the 

 third presacral. Professor Gegenbaur mentions no such condition, while Professor 

 Hoffman has only found it 3 in one specimen of Polychrus marmoratus. This was not 

 the case in another specimen 4 of his, thus showing (what our own dissections have 

 convinced us of) that two individuals of the same species may present considerable 

 nerve-differences. The sciatic nerve (33) gave off, as usual, a branch high up to the 

 obturator interims muscle (23). 



In Agama the lumbar plexus was formed by three roots. The most preaxial was the 

 fourth presacral nerve (2) ; the second root consisted- of the greater part of the third 

 presacral nerve (9), the rest of that nerve (46) going to the sacral plexus. The most 

 postaxial root consisted of a slender branch of the second presacral nerve (11). This 

 slender branch passes over the before-mentioned outer slender branch (46) so as to form a 

 marked cross on each side of the body. The obturator nerve (5) was principally formed 

 by the fourth presacral (2), but received an accession from the third presacral ; it gave off 

 a branch (7) to the iliacus. The crural nerve was formed mainly from the third presacral 

 nerve (9), but received a branch from the fourth presacral and also the slender branch 

 before mentioned (11) from the second presacral. 



Iguana tuberculata. (Plate LXVIL fig. 1.) 



Professor Gegenbaur does not appear to have examined the sacral nerves of this 

 species ; but Professor Hoffman 5 describes the sciatic as arising from three roots, namely, 

 1, a bifurcation of the second presacral nerve (i. e. the ilio-lumbar nerve) ; 2, the whole 

 of the first presacral nerve ; and 3, a branch from the intersacral nerve. No branch is 

 described or figured as going to it from the first postsacral nerve. The lumbar plexus 

 is described as formed by four roots : — 1, the fourth presacral nerve ; 2, the preaxial 

 bifurcation of the third presacral ; 3, the postaxial bifurcation of the same third pre- 

 sacral ; and 4, by the preaxial bifurcation of the second presacral. The first and second 

 roots unite together to form the obturator nerve, and the third and fourth roots unite 

 together to form the crural nerve. 



We have examined two individuals of Iguana tuberculata, for one specimen of 



1 L. c. p. 201. 



2 " Vor allem ist die Betheihgung postsacraier Nerven am Plexus ischiadicus ganzlich aufegehoben.". 



3 L. c. p. 178, fig. 13. " L. c. fig. 12. 



' i L.c. pp. 176, 177, fig. 11. His figure does not agree with his description as regards the obturator nerve. 

 SECOND SERIES. — ZOOLOGY, VOL. I. 3 Z 



