CIRCULATION OF BATRACHIANS. 



67 



3. The apparatus of the circulation undergoes changes cor- 

 responding to those experienced by the organs of respiration. 

 The heart of Batrachians, like that of most reptiles, is composed 

 of two auricles and a single ventricle, from which arises a great 

 artery ; at its base, this artery is swelled into a contractile bulb, 

 and soon after bifurcates. When the animal breathes by bran- 

 chiae alone, the blood, forced by the ventricle, is distributed to 

 these organs, from which the greater part of it, goes to the 

 dorsal artery, the branches of which ramify in the various 

 organs. In fishes this liquid follows the same course. But when 

 the lungs are developed, the disposition of the circulatory apparatus 

 changes : there is established a direct communication between the 

 vessels which carry the 

 blood to the branchiae, 

 and those that receive it 

 from those organs, so that 

 it is not necessary for this 

 liquid to pass through the 

 respiratory apparatus to 

 reach the dorsal artery, 

 and, through it, the dif- 



fer 1. 



&r2 



Fig. 28' 



6r3. 



3. 



ap 



ap 



av 



ferent parts of the body. 

 The artery, (Fig. 28, a.) 

 which arises from the ven- 

 tricle, and which could be 

 compared at first to a 

 branchial artery, then be- 

 comes the origin of the CIRCULATION IN A PERFECT BATRACHIAN. 

 dorsal vessel, and with it constitutes a true aorta, certain branches 

 of which, that go to the lungs, are developed at the same time, 



ing through these organs ; the same letters indicate the same vessels as in 

 the preceding figure, and it will be observed that the anastomosing branches, 

 (1. 2. 3.) which, in the Tadpole, were capillary, and did not give passage to 

 a very considerable quantity of blood, are here of some size, and that they 

 seem to be continuous with the branchial vessels rather than with the arte- 

 ries coming from the heart. The pulmonary arteries are also much developed. 

 * Explanation of Fig. 28. The same parts in the perfect animal, indicated 

 by the same letters as in Figs. 26. and 27. Here the vessels of the branchiae 

 have become rudimentary, and the pulmonary arteries much developed ; the 

 vessels which convey the blood to the middle branchiae are continuous, without 

 interruption, with those (c.) that receive this liquid after its passage through 

 these organs, and thus form an aortic cross, on each side of the heart. 



3. What are the characters of the heart in Batrachians ? What are the 

 peculiarities of the circulation in Batrachians ? In what respect does the 

 circulation of Batrachians differ from that of fishes ? Does the aorta in 

 Batrachians circulate pure arterial blood ? 



