HIGH SCHOOL ZOOLOGY. 



159 



tions of the lung- walls or sac-like projections thereof, such as 

 occur in the Sauropsida. The upper part of the windpipe is of 

 great interest, however, because it is first in the Mammalia, in 

 which we meet with the chai-acteristic arrangement of the hard 

 parts of the larynx, which attain their perfection in the vocal 

 organ of man. In addition to the cricoid and arytsenoid car- 

 tilages, such as are met with in the lower forms, a third, the 

 thyroid, is developed which forms the " Adam's apple " of the 

 human larynx and serves with the arytfenoids for the attach- 

 ment of the vocal cords. A membrane stretches from the 

 outer edge of the thyroid cartilage to the thyi'ohyals (§ 6), and 

 the larynx is thus brought into connection with the hyoid bone. 

 16. We saw that the great respiratory activity of the birds 

 requires a complete separation of the arteiial and venous blood 



in the heart : this is eflected 

 in the same way in the niam- 

 maLs, the right auricle and 

 ventricle, respectively, leceiv- 

 ing the venous blood from the 

 body and pumping it through 

 the lungs, while the left 

 auricle and ventricle, i-es- 

 pectively, receive the aerated 

 blood from the lungs and 

 pump it through the system 

 (Fig. 105). Some difference 

 is to be observed in the great 

 vessels which come off from 

 the heart, notably as to the 



jvk ha 



Fis. ins. -Heart and Lungs Of Man ^.^^^ ^^^.^-^ ^^.^^ ^j^-^j^ j^ 



a, deseenrtina: aorta ; Ik, Jeft, Tk, right o 

 ventricle; rvk. ri'^'ht auricle; ha, inferior ^J^q fourth arterial arch of 

 vena cava ; 1, trachea ; e and f, the two caro- 

 tids ; heside these, d and g, the two internal i[^q Jgf^ j^q^ of the ridlt side, 

 jusular veins ; c and i, subclavian arteries; ' i • , 



b and m, subclavian veins. aS in birds. The blood wllich 



