72 BATRACHIA. 
6. The heart has a single ventricle, and apparently a single auricle, which is, 
however, subdivided into two chambers. 
Remarks. Although the order Reptilia embraced but few animals in the time 
of Linnaeus, yet the numerous discoveries of recent herpetologists of new species, 
made it necessary to subdivide this order into three very natural families, from 
the great difference in their external forms, which is always attended with a 
corresponding internal organization. 
These sub-orders were well named by Oppel—Apoda, Ecaudata, and Caudata. 
Of the first, or Apoda, there are none in the United States. 
