PLEXUS AND SACRAL VERTEBRJE OF LIZARDS. 



523 



species, and even in different individuals (apparently, from Gegenbaur's and Hoffman's 

 works) of the same species. Shall we, then, consider that the nerves are the fixed points ? 

 If so, it is evident that we must extend our survey, and consider the nervous conditions 

 of the sacral region in other orders and classes of animals. 



Crocodiles present no marked differences from Lizards, according to Gegenbaur, 

 who describes the sciatic nerve as formed from three roots — one intersacral, one pre- 

 sacral, and one postsacral, the intersacral one being much the largest. Professor Hoff- 

 man 1 agrees in this. 



In Tortoises, according to Gegenbaur 2 , there are four roots to the sacral plexus — 1, 

 one postsacral, as large as the next preaxiad, *. e. 2, the intersacral, and 3 and 4, two 

 presacrals, one of which is the largest of all. According to Hoffman 3 also there are four 

 roots ; but he represents the postsacral root as by far the most slender, and the inter- 

 sacral root as larger than either of the two presacral nerves. 



ris. 3. 



Fig. 4. 



Nerves of Alligator (from Hoffman). 

 C, crural nerve ; i, ischiatic ; o, obturator ; s, s, 

 vertebrae with, expanded transverse pro- 

 cesses ; 1 pr-3 pr, presacral vertebrae ; 

 1 po, postsacral vertebra. 



Nerves of Tortoise (from Hoffman). 

 c, crural nerve ; i, ischiatic nerve ; o, obturator 

 nerve ; s, s, vertebra? with expanded trans- 

 verse processes ; 1, 2, 3 and 4, 

 vertebras. 



In all the Reptilia enumerated, the transverse processes which abut against the ilium 

 are wholly or in part parapophysial, and are in serial relation to (serial homolOgues of) the 

 capitular processes (or the capitular parts of the whole transverse processes) of the more 

 preaxial vertebra. The junction of the sacral vertebra with the ilium is much post- 

 acetabular in Saurians, but in Crocodiles and Tortoises (some at the least) it is about 

 opposite the acetabula. 



The Sacral Region oe Batkachians. 



Here we have almost always but a single vertebra with enlarged transverse pro- 

 cesses abutting against the ilium. 



In the tailed Amphibia we have in Cryptobranchm japonicus, according to Professor 

 Humphry 4 , a sciatic nerve formed from three roots, two of which are preaxial of the 



1 L. c. p. 187, fig. 14. 2 L. c. p. 200. s L. c. p. 167, fig. 5. 



4 Journal of Anat. and Physiol. 1872. The muscles and nerves of C. japonicus, p. 51, woodcut. 



