THE LIMBS OF AMPHIBIA. 



157 



In the genus Amphiuma, the limbs have each either two 

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

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



x.st 



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

 scapula is removed : flc, scapula ; s.sc, supra-scapula ; ^.«c., preacapular process ; cr., 

 coracoid ; d-or., epicoracoid ; cr.f., coracoid fontanelle. The bar which bounds this Id 

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

 xiphistcraum. 



are tridactyle, the posterior didaotyle. Menohranchus has 

 tetradactyle feet, while in the other TTrodela the anterior limbs 

 are tetradactyle, the posterior pentadactyle. The Satrachia 

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

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

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

 in Proteus, present little deviation from the typical number 

 and arrangement (Fig. 11, p. 33), remain unossified ; in the 

 other TTrodela, and in the JBatrachia, they are for the most 

 part ossified. 



In the Satrachia, the posterior limbs 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 two proximal, 

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

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

 The limbs of the Labyrinthodonts were feeble in compari- 



