372 



AVES 



large and muscular, taking the space usually filled with pectoral 

 muscles and the anterior part of the sternum. The young birds 

 when first hatched have a clawed thumb and index finger on the wing, 



Nucleus of ^ 



Pander 



l-otebra-^ 



Blastoderm 



,. NecK of iQtebra 



Inner- She/I 



Outer- £helf 

 membrane 



White yolk--' 

 yel/ow YolH 



■-CholQZO 



Dense a/bumen 



'' l^e.ss dense a/bumen 

 ^ Vitellines membr-ane 



Fig. 208. Diagram of the hen's egg in longitudinal section. (After Lillie. Courtesy 



of Henry Holt & Co.) 



resembling the condition in Archeopteryx. They are able to climb 

 about the branches and find their own food, using their feet and wing 

 digits. 



fhoryn^eof poucnes I to JOT 



Anr. carc//na/ v. 

 Aortic Qr-dh JS"-, 



Aortic ortzriei 

 TTandlZI 



Trocnsa 



/\trium - 



Duct Of Cuvier •- 



Stnus s/enosus ' 



i- iver - 

 Ventricle- 



Dorsal aorta 

 Mesonephros ' 

 F<ost. cardinal 

 Hind 



Aortic arch I 



(disopfieorln^) 



carotid o . 



Ext. iliac 

 CI 



EKt. carotid a. 



-Ant. card /not v. 



Allantoic vein 

 Yolk stocK 

 Omph. mes. v. 

 Ornpti. mes. a. 



Allonf-oic vein 



A //onto is 



Allantoic artery 

 Proc todoe am 



Post-anal <jut 



Fig. 209. Internal organs of a four-day chick. (From Lillie, Development of the Chick. 



Courtesy of Henry Holt & Co.) 



