10 



aeration, and in part, in its mixed condition, to the aorta and 

 arteries of the body. In the birds and mammals the blood is 

 fully oxygenated through the functional activity of a fourth 

 cavit}^ of the heart, and is therefore warm. 



The batrachians were the first air-breathing vertebrates. 

 The fishes and other low forms breathe oxygen existing free 

 in the water, instead of atmospheric air. Many modern anat- 

 omists use the term amphibia for the batrachia, but the latter 

 name was first properly used by Brongniart to define a cor- 

 rectly limited group and is retained. 



The batrachians are divided into three groups, one of which 

 embraces extinct forms more nearly related to the fishes than 

 to either of the others. The second division includes the sala- 

 manders (Ccecilia and Urodela) and the third the frogs and 

 toads. To this is given the name Salieniia. 1 This division is 

 the most specialized and the farthest away from the type. 



The Salientia are separated from other batrachia by diversi- 

 ties in anatomical and skeletal structure, especially in the loss 

 and coosification of various parts of the skeleton. In common 

 with Urodela (salamanders) they have a naked skin, four 

 limbs, three cavities in the heart and lungs, while the latter 

 receive ox} T gen, active elimination of carbon dioxide takes place 

 through the skin. 2 They differ noticeably from salamanders 

 in having no ribs, no tail in the adult, and in the anchylosis of 

 the radius and ulna and tibia and fibula. 



1 Latin, Salio (ppr. ), salien(t-)s, leap. 



2 It has recently been discovered that several of our adult salamanders 

 lack lungs and gills, and that the respiratory function is carried on by 

 other structures or organs. Professor Harris H. Wilder of Smith Col- 

 lege, has described this peculiar condition and arrived at the conclusion 

 that respiration was probably carried on by the skin and perhaps to some 

 extent by the mucosa of the intestine. 



In a paper read by G. S. Hopkins, of Cornell University, before the 

 American Association for the Advancement of Science, August 24, 1896, 

 attention is called to the rich supply of blood-vessels of the skin, which 

 are so close to the surface as to admit of ready interchange of the gases 

 of the blood and air. Mr. Hopkins says that it is often possible to dis- 

 tinguish between salamanders with and without lungs by examination of 

 the heart alone. In the lungless forms examined the left auricle is very 

 small and no pulmonary vein was found opening into it. The sinus 

 venosus, instead of opening into the right auricle only, opens more freely 

 into the left auricle than into the right. Mr. Hopkins examined eight 



