110 



Fio. T6. — Plan of Ciicnla- 

 tiou in Fishes: a, auri- 

 cle ; b, ventricle : c, bran 



COMPARATIVE ZOOLOGY. 



SO also do the ventricles. The course 

 of the current in Birds and Mammals 

 is as follows : the venous blood 

 brought from the system is discharged 

 by two or three large trunks" into 

 the right auricle, which immediately 

 forces it past a valve " into the right 

 ventricle. The ventricle then con- 

 tracts, and the blood rushes through 

 the pulmonary artery past its semi- 

 lunar valves into the lungs, where it 

 is changed from venous to arterial, 

 returning by the pulmonary veins to 

 the left auricle. This sends it past 

 :ei:l"S;g''"biood tl>e mitral valves into the left ventri- 

 from the giiie, d, and q\q which drives it past the semilunar 



uniting in the aorta, /; ffy 



veuacava. valves into the aorta, and thence, by 



its ramifying arteries and capillaries, into all parts of the 

 body except the lungs. 

 From the systemic cap- 

 illaries, the blood, now 

 changed from arterial 

 to venous, is gathered 

 by the veins, and con- 

 veyed back to the heart. 

 The_ Rate of the 

 Blood - current gen e r- 

 ally increases with the 

 activity of the animal, 

 being most rapid in 

 Birds." In Insects, 



however it ifS fomnnra ^'o- f6.— A, Plan of Circnlntion in Amphilii.i nir. 



now ever, IC is COmpara- Heptiles; B, Plan of Circulati.m in Birds and 



tively slow* but this is Mammals; a, right auricle receiving venous 

 , ' . . blood from the system ; b, left auricle veceivin" 



because the air is taken arterial blooa from the Inngs; c, c", ventricles. 



d, c,/, systemic artery, vein, and capillaries; f?, 

 pulmonary artery ; h, k, vein and capillaries. 



to the blood — the whole 



