Ichthyopsida 



455 



legs. Behind the ninth, or sacral, vertebra is a long, straight, un- 

 segmented rod of bone, the urostyle, whose mode of development 



Oe 



Fig. 351. Vertebral 

 column of frog; dorsal 

 view. (Ob) Neural arch of 

 first vertebra; (Oc) uro- 

 style; (Pa) articulating 

 processes; (Ps) neural 

 spine of trunk vertebra; 

 (Pf) transverse process; 

 (Pic) transverse processes 

 of caudal vertebrae which 

 are fused into the uro- 

 style; (/?) ribs; (Sg) right 

 facet articulating with 

 right occipital condyle of 

 skull; (SW) sacral verte- 

 bra; (Tb) first (cervical) 

 vertebra. (Courtesy, 

 Wiedersheim : "Grundriss 

 der vergleichenden Anat- 

 omie der Wirbeltiere," 

 Jena, Gustav Fischer.) 



indicates that it is constituted of several (perhaps in some cases as 

 many as 12) vertebrae fused together (Fig. 351). In vertebrates in 

 general, it is customary to designate 

 as "caudal" all vertebrae that lie 

 behind the sacrum. In this sense the 

 urostyle ("uro-" meaning "tail") 

 is a caudal structure, but in a strict 

 sense it is not caudal and the adult 

 anuran has no tail. The vertebrae 

 in Anura are more solidly ossified 

 than in most other amphibians and 

 the adults ordinarily do not retain 

 vestiges of the embryonic noto- 

 chord, whereas in many adult 

 urodeles remnants of the notochord 

 may, to varying extents, persist. 

 Further, in contrast to "lower" 

 (less specialized) urodeles whose vertebral centra are commonly bicon- 

 cave (amphicoelous) like those of fishes, the centra of Anura are usu- 



Fig. 352. Head of bullfrog, Rana 

 cafesbeiana, showing tympanic mem- 

 brane just behind eye. (By permission 

 from "Biology of the Amphibia," by 

 G. K. Noble, copyrighted 1931. 

 McGraw-Hill Book Co., Inc.) 



