522 



MESSRS. MIVART AND CLARKE ON THE SACRAL 



presacral nerves unite to form the lumbar plexus ; in Monitor it is the first, second, and 

 third which do so. In Iguana there is a branch to the iliacus (7) which was not detected in 

 Monitor. In Iguana the semimembranosus is not supplied from the first postsacral nerve ; 

 in Monitor it is so supplied. In Iguana the intersacral and first postsacral nerves unite 

 by two commissures ; in Monitor by only one. In Iguana the femoro-caudal is supplied 

 by the sciatic nerve ; in Monitor by the first postsacral. In Iguana more of the first 

 postsacral nerve joins the sciatic plexus than in Monitor, and the semitendinosus and 

 pyriformis are, in Monitor, supplied by the first postsacral instead of, as in Iguana, from 

 the sciatic. In Iguana the obturator internus has a branch to itself, which comes from 

 the root of the sciatic. In Monitor it is supplied, in common with the gracilis and 

 semimembranosus, by a branch which is given off by the most preaxial root (12) of the 

 sacral plexus. 



Fig. 2. 



General Condition op the Nervous and Osseous Structures of the Sacral 



Eegion in Lizards. 



It appears, then, that in Lizards generally (judging from the specimens we have 

 examined and from the observations of Professors Gegenbaur and Hoffman), the 

 lumbar plexus may be formed by from two to three roots, and that the most preaxial of 

 them is never in advance of the fourth presacral nerve, while the most 

 postaxial root is never more postaxial than the first presacral nerve. 

 Only in Monitor and Cliamceleo have we found this plexus to have 

 a root as postaxiad as the first presacral nerve, and neither of the 

 authors referred to represents it with so postaxiad a root. 



The sacral plexus may have from three to four roots, but we have 

 generally found four. The most preaxiad of these is the lumbo-sacral 

 nerve (12), formed from the third presacral nerve (as sometimes in 

 jPolychrus),ov from the second presacral (as in Grammatophora, Lacerta, 

 Teius, Agama, and Iguana), or from the first presacral (as in Monitor). 

 The most postaxiad root is from the second postsacral, as in our spe- 

 cimens of Cliamceleo. 



Generally, according to our examinations, the roots are the first 

 (or first and second) presacral, the intersacral, and the first postsacral. 

 According to the authors referred to, it is generally the first and second 

 presacral and the intersacral, and never any postsacral. It cannot be 

 doubted, however, but that the roots preaxiad to the first vertebra 

 with enlarged transverse processes may vary in number from one to 

 three, and that there may be two, one, or none behind the posterior 

 vertebra with enlarged transverse processes. In all the Lizards re- 

 ferred to there are two such vertebrae with enlarged transverse pro- 

 cesses abutting against the ilium. Are both these vertebrae sacral or 

 neither ; or if only one, which ? 



The relation of the nervous roots to these transverse processes varies from species to 



Nerves of Polychrus 

 marmoratus in two 

 individuals (from 

 Hoffman). 



c, crural nerve; i, 

 ischiatic nerve ; o, 

 obturator nerve ; 

 1 pr-4 jor, presa- 

 cral vertebrae; lpo, 

 postsacral vertebra ; 

 s, s, vertebrae with 

 enlarged transverse 

 processes. 



