THE BATRACIIIA OF NORTH AMERICA. 



247 



The presence or absence of maxillary teeth was formerly regarded by 

 the author, after Dameril and Bibron, as of primary value in the defini- 

 tion of the suborders. On account of the absence of teeth, a division 

 Bufoniformia was distinguished from the Arcifera; and the tooth-bear- 

 ing Fermisternia were called Raniformia. I, however, now follow Bou- 

 lenger in dropping these divisions, since the absence of teeth is some- 

 times of little systematic significance. 



In the arciferous type of scapular arch the opposite halves are capable 

 of movements whicli contract or expand the capacity of the thorax; in 

 the Firmisternia the opposite halves abut against each other so as to be 

 incapable ot movement, thus preserving the size of the thoracic cavity. 

 This arrangement has an important bearing on the comfort, and perhaps 

 health, of the female while in connection with the male. The embrace of 

 the fore-legs of the latter behind the axillse of the former is very energetic, 

 and is maintained by various structural aids. Thus in many species the 

 males develop rough and even spinous horny i)lates on the inner supe- 

 rior side of the thumb, which presses against the thorax of the female. 



The flrmisteruial structure is a modification of the arciferous, which 

 comes later in the history of growth, and ])robably in geological time. 

 During the early stages the Firmisternia have the movable shoulder 

 girdle which characterizes those of the arciferous division, the consoli- 

 dation constituting a modification superadded in attaining maturity. 

 Furthermore, young Salientia are toothless, and one section of the spe- 

 cies of Arcifera never acquire teeth. In these (the Bufonidse) we have 

 a group which is imperfect in two points instead of one. 



Fig. 59. 



Shoulder girdles of Auura. Fig. a of the arciferous type (Scaphiopus holbrooki). Fig. &, liana teni_ 

 poraria, tadpole with budding limbs. Fig. c, do., adult, flrmisternial type. Figs, b and c from Parker. 



As primitive Batrachia are toothed, it is evident thar, the toothless 

 condition of the Bufonidte and some other families is due to retar- 

 dation or degeneracy. The arciferous sternum is, on the other hand, a 

 primitive condition, since it prevails in the Urodela, and also in the 

 Stegocephali and Eachitomi of the Carboniferous Age, in the latter 

 associated with median sternal elements. The roofing in of the 

 Eustachian tubes seen in the Aglossa is also a character superadded to 

 the primitive condition, as the loss of tongue is a case of subtraction. 



