PLEXUS AND SACRAL VERTEBRAE OF LIZARDS. 525 



formed of three roots, one preaxiad and another postaxiad to the iliuin-supporting ver- 

 tebra, while the third root is still more postaxiad. In Batrachians the transverse pro- 

 Fig. 7. Fig. 8. 



Nerves of Dactylethra, fig. 7, and of Bana and Eyla, fig. 8 (from Hoffman). 

 e, crural nerve ; i, ischiatic nerve ; o, obturator nerve ; lprSjpr, presacral vertebras ; s. vertebra with enlarged 



transverse processes. 



cesses abutting against the ilium are parapophysial, not diapophysial, in nature, thus 

 agreeing with those of Reptiles. 



The Sacral Region oe Mammals. 



In Man the great sciatic nerve has six roots, the most preaxial of which (the fourth 

 lumbar nerve of anthropotomy) may be called the second presacral of the nomenclature 

 here adopted, since the next postaxiad (the fifth lumbar nerve) comes out preaxial 

 to the first transverse process abutting against the ilium, and would thus be our first 

 presacral. The next postaxiad (the first sacral nerve of anthropotomy) may be reckoned 

 as equivalent to what we have termed intersacral in Lizards, while the remaining three 

 may be reckoned as equivalent to our first, second, and third postsacral nerves. 



Now if we take the nervous relations as our exclusive test, then the vertebra postaxial 

 to the first sacral root of Lizards must be the homologue of the first sacral vertebra of 

 Man ; and in that case this vertebra would, in Monitor and Chamceleo, be the first with 

 expanded processes abutting against the ilium. In Iguana, Terns, Lacerta, and Gramma- 

 tophora, however, it would be the vertebra preaxiad of such first ihum-joining vertebra, 

 while in Agama and, at least sometimes, in JPolychrus x , it would be the second vertebra 

 in front of such ilium-joining vertebra. 



In an inferior mammal, such as the Cat (PI. LXVI. fig. 7), we found the sacral plexus 

 to be formed by four roots, two very much larger than the others. The most preaxial (12) 

 root (the largest but one) is formed by part of the nerve coming out between the pen- 

 ultimate and ultimate lumbar vertebras ; the next (the largest) comes out (21) in front 



1 See ante, woodcut, fig. 2, p. 522. 

 SECOND SERIES. — ZOOLOGY, VOL. I. 4 A 



