THE LliTBS OF AMPHIBIA. 



157 



In the genus Amphiwna^ the limbs have each either two 

 or three digits. In Siren, the anterior limbs, which alone 

 exist, are ttSee- or four-toed. In Proteus, the anterior limbs 



icst 



Fia. 57. — The sternum and pectoral arches of a Frog, seen from above. The left supra- 

 scapula is removed: sc, scapula; s.sc, supra-scapula; ^)..<!c., prescapular process ; cr., 

 coracold ; e.cr., epicoracoid ; cr.f., coracoid fontanelle. The bar which bounds this in 

 front is the precoracoid, and bears the clavicle : o.st, omosternum ; st, sternum ; x.st^ 

 xiphisternom. 



are tridactyle, the posterior didactyle. 3Ienohranchus has 

 tetradactyle feet, while in the other tirodela the anterior limbs 

 are tetradactyle, the posterior pentadactyle. The Batracliia 

 have four digits, with or without a rudiment of another, in the 

 fore-limb, and five in the hind-limb. In the perennibranchiate 

 Tirodela, the cartilages of the carpus and tarsus, which, except 

 in Proteus, present little deviation from the typical number 

 and arrangement (Fig. 11, p. 32), remain unossified ; in the 

 other Urodela, and in the Patrachia, they are for the most 

 part ossified. 



In the Patrachia, the posterior lunbs are much longer than 

 the anterior. The radius and the ulna in the fore-limb, and 

 the tibia and fibula in the hind-limb, are fused together into 

 one bone. The carpal bones no longer present the typical 

 arrangement ; and, in the tarsus, there are tvvo proximal, 

 greatly elongated, cylindrical bones, which take the place of a 

 calcaneum and an astragalus, while the distal series is reduced. 



The limbs of the Labyrinthodonts were feeble in compari* 



