272 



COMPARATIVE ANATOMY. 



l. inrsonr-phros (see p. 296), and body-walls (Fig. 215, VC, EC 

 alld Fig. 21G,0/.r, F.Ca). 



The antrriiir cardinal ruins, \\ hi< h ivturn UK- blood from the head and 

 .int'TicT portion of the body persist, and ;-i\f ri.-i- 1" the large jugular veins 

 of the adult (coni]>. FL's. -17 t<> L'J'.t 1 : tin- posterior cardinals soon become 

 largely oblrti-ratrd. and are re-placed by thr a/. v;4s and vertebral vein:-, 

 and more especially by the postcaval (vma cava posteriory inferior) 

 l-'i':s. :.' 17 to lii'.i . For farther details as to the venous circulation, e.<7. the 

 portal system (which becomes ot.-ibli-hed in Fi.-ljr-; b\- tin- subintestinal 

 v.-iu;. tin- jvadi-r is n-r.-nvd to \'"\<. 217 to 219. 



AA 



FIG. 216. DIACIIAM OF TIIK rincri.ATioN ov TIIF, Yoi,K-S.\c AT THE END OF 

 Tin: TIIIIMI D\v UK Ixcrr.ATiox IN TIIK CHICK. (After Balfour.) 



If, heart: AA, the second, third, and fourth aortic arclu-s: the first has become 



oltliti-ratrd in its nu-dian iiortion, but is cuntiinu-d at its proximal end as the 

 external run.tid, and at its distal md as tin- ind-nial carotid ; Ao, dorsal a 



black. Tin- \vhnh- i 



to In- viewed from below. 



has i.rcn removed tnuii the c<^, and is supposed 

 Hence the left is seen mi the ri^ht, and r/<r fc/-.v<?. 



To ivturn onco nioro to tbc arterial system : We must consider 

 next tin- t\vu Inaiicln-s of the dorsal aorta known as the allantoic 

 arteries 'Fi-. -15, All). As tlu-ir name implies, these arteries 

 branch outov-T the allantois, which arises as an outgrowth from 



