138 



AMPHIBIA 



CLASS II 



sc- 



The basioccipital region and auditory capsules are ossified ; the parasphenoid 

 is inverted T-shaped; and the pterygoid, palatine, and jugal are well 



developed, the last-named joining the 

 maxilla in front and quadrato- jugal behind. 

 Small, bristle-like pleurodont teeth occur on 

 the jaw-bones and vomer, or may be entirely 

 wanting. 



The pectoral arch (Fig. 233) is remark- 

 able for its large-sized scapular element, 

 which is commonly divided and incom- 

 pletely ossified, and joins with the coracoid 

 and precoracoid. The sternum is also large 

 and more or less cartilaginous ; of its three 

 ossified portions, the anteridr is called the 

 omosternum ; the middle piece is the 

 sternum proper ; and the posterior, which 

 terminates in a semicircular cartilaginous 

 expansion, is the xiphisternum. Ulna and 

 radius are fused, the two rows of small 

 carpals are ossified, and the manus is pro- 

 vided with four digits. 



The three elements of the pelvic arch are 

 coossified at the acetabulum on either side 

 to form a single piece, which joins its fellow 

 in a median symphysis. Tibia and fibula are fused, the two bones forming 

 the proximal row of the tarsus (astragalus and calcaneum) are much elongated, 

 and the pes has five digits. 



Fossil Anura are rare, the oldest clearly identifiable remains occurring in 

 the Eocene of East India (Oxt/glossus pusillus, Owen sp.) and Wyoming. A few 



Fig. 231. 



Vertebral column of Rana esculenta. A, Dorsal 

 and B, Ventral aspect. l/l« a ^j Atlas ; d, Trans 

 verse process ; z, Anterior ; z', Posterior zygapo 

 physes ; sc, Sacral vertebra ; coc, Coccyx. 



A 



C 



.Islsr 



■(W 



Ihiv 



JMx: 



Ml 



:E:xo Scrj 



Fig. 232. 



Skull of Rana esculenta, Linn. A, From above. B, From the side. C, From below. Pmx, Premaxilla ; Mx, 

 Maxilla; Na, Nasal; FrPa, Fronto-parietal ; Sq, Squamosal (tympanic); QvJ, Quadrato-jugal ; hy, Hyoid ; md, 

 Lower jaw ; PSph, Parasphenoid; Vo, Vomer; PI, Palatine; Pt, Pterygoid; Eth, Ethmoid (Orbitosphenoid) ; 

 P, Petrosal. 



genera are known from the Upper Eocene, Oligocene, and Lower Miocene of 

 Southern France, Northern Italy, and Germany, Rana and Palaeobat melius 

 being the commonest forms. Phosphatised mummies both of Rana and Bufo 

 occur in the Eocene (or Oligocene) Phosphorites of Quercy. The Miocene 



