20 



ZOOLOGY. 



The first half, which receives the blood, poor in 

 oxygen, that is returned from the body, and sends it 

 on to the lungs, lies on the right, and is termed the 



right half. The second half, 

 which receives the richly 

 oxygenated blood from the 

 lungs, and pumps it to the 

 various parts of the body, is 

 termed the left half (Fig. 9 

 and explanation). 



In the arrangement just 

 described, which is found in 

 Mammals and Birds, the 

 blood returning from the 

 lungs is propelled with new 

 force through the body, and 

 therefore circulates very 

 quickly, so that the various 

 parts receive a relatively 

 large amount of oxygen in 

 a short time. It is therefore intelligible that Birds 

 and Mammals develop more warmth than Fish, 



They possess a special, 

 constant body tempera- 

 ture, somewhat different 

 in difierent species, but 

 usually lying between 

 98° and 104° Fhr., and 

 they are called warm,- 

 blooded animals. 

 In Reptiles (snakes, 



FIG. 10._Diagram of the Heart of a Reptile. }^fT'^' /tc.), the twO 



Between the right (r.JT.) and left if.K.) haiVCS 01 the heart are 



ventricles Is a perforated partition. r.F.i., „ j. j.- i t ,• 



right anriole; !.r.s:., left auricle; ff.li., nOt entirely Qistuict, 



vena cava, carrying back the blood which oinppfhAro to an r^Ti^nn'^™ 



has traversed the body into the right ^'^^^^ mere IS an Opening 



anricle; i.orJ., pulmonary artery; L.D., in the Partition - Wall 



puhnonary vein; .flo., aorta. , , jjo/i-uiuiuii wdjj. 



between the two ven- 

 tricles. As a consequence of this, the poorly oxygenated 



Fig. 9 — Diagram of the Mammalian 

 Heart. 1, right, 2, left ventricle ; 

 3, right, 4, left auricle; 5, su- 

 perior, 6, inferior vena cava; 7, 

 pulmonary artery forking into 

 branches for right and left lungs ; 

 8, the four pulmonary veins; 9, 

 the great body-artery (aorta); the 

 arrows indicate the direction of 

 the blood stream. 



Z. art. 



M.V, 



T.V.K. 



J-.K 



