24 ANURA CHAP. 



Strictly speaking, or rather in anatomical parlance, the 

 Vertebrate tail begins with the first post-sacral vertebra. In 

 the Anura that portion of the whole tail has retained most 

 cartilage, and has become the coccygeum, which is required as 

 a " backbone " for the often enormous belly. This require- 

 ment is an outcome of the great shortening of the trunk proper 

 (if the trunk be defined as ending with the pelvic region), and this 

 shortening of the trunk is again intimately connected with the 

 jumping mechanism, enlargement of the hind-limbs, elongation 

 of the ilia, and throwing the fulcral attachment forwards as 

 much as possible. The pre-acetabular ilio-sacral connection is 

 carried to the extreme in the Anura. 



The shoulder-girdle and " sternum " are more complete than 

 in the Urodela, there being also a pair of clavicles, fused with 

 the precoracoidal bars. The whole apparatus presents two types. 

 In the arciferous type the coracoids and precoracoids retain 

 a great amount of cartilage in their distal portions, and these 

 cartilages (the epicoracoids of some authors) overlap each other 

 movably on one another, the right usually lying ventrally upon 

 the left. The epicoracoidal cartilage of each side, by connecting 

 the distal end of the coracoid with the precoracoid of the same side, 

 forms an arc, hence "arciferous." In the firmisternal type 

 the epicoracoidal cartilages are much reduced, and, instead of 

 overlapping, meet in the middle line and often fuse with each 

 other, forming thereby a firm median bar, which connects the 

 ventral ends of the precoracoids with those of the coracoids. 

 This type is morphologically the higher and more recent, and 

 passes in the larval stage through the arciferous condition. 

 It is restricted to the Ranidae, Engystomatinae, and Aglossa. 

 Although these two types afford an excellent distinctive char- 

 acter for the main divisions of the Anura, they are to a certain 

 extent connected by intermediate forms in such a way, that, for 

 instance, in Bufo and among Cystignathidae in Ceratophrys, the 

 two opposite epicoracoidal cartilages begin to unite at the 

 anterior end. 



In many Engystomatinae the precoracoids together with the 

 clavicles are much reduced, sometimes to thin ligaments, being 

 in this case mostly curved back and lying closely against the 

 coracoids ; or they may be lost completely. Very rarely the 

 precoracoidal bars are actually much stronger than the coracoids, 



