IHI: OBG km "I' -iin: p \n. i..\\KK OR ME.- 



(A) '/A. Fir* /' ' r -..'Htal Condition* of the Large VeueU. Vitdlin* 

 Cin and Plu< fion. 



At both en<U, in front ;u,,I behind, the heart i- continuous with 

 tin- trunks ,-f Mo.,: i, have been established at the same 



time with it. Tin- anterior oc ait. he cardiac tube is 



elongate.! into an unpaired vessel. the fnnicu* arteriout t which con- 

 tinues the forward course under the head gut, and is divided in the 

 re-ion of die tirst \i-c,-;-ai arch into two arms, which embrace the 

 head-gut on the right an 1 leti an-1 ascend within t ho arch to the 

 dorsal surtac. ..t t!u emhi -\M. Here they bend around and run back- 

 ward in the longitudinal a\i- of tin- l-o-lv to the tail .-nd. These 

 t\\o \TS>I -Is are the primitive aorta* (figs. 107, 116 oo); they take 

 their i-onr-e on either side of the chorda dorsalis, above the entoderm 

 and In-low the {.riinitive segments. They give off lateral branches, 

 among which the tirt'-rnr- iti/>halomesenterica! are in the Amniota 

 tlistin.iruisln d by their great size. These betake themselves to the 

 yolk-sac and conduct the greatest port!--: Mood from th 



primitive aorta? into the area vasculosa, where it goes through 

 vitelli.' 



In the Chick, the condition >f which form the ba- 

 mt (tig. 303), the two vitelliim arteries (K.< 



the aortie at some distance from their tail-ends, and pa. nilly 



from the . inhrynic fun.lai: ,, -en entoderm and visceral n 



layer into the area pelh verse the hem- 



selves in the vascular area. They are here resolved into a fine 

 work of vessels, which lie, as a cross section (fig. 116) sho\\ 

 inesenchyme between the entoderm and the visceral : 

 and which are >harply bounded a' edge (toward 



viulline an -a) by a large marginal vessel (fig. 303 S.T), the sinu> 

 minalis. The latter forms a ring which is e\ closed, \ 



the except ion -f a >inall region which lies in front, at the place 

 where the nnniotic sheath has been developed. 



I rom the vascular area the blood is collected into several large 

 venous trunks, hy means of \\hich it is conducted back to the heart. 

 From the front part of the marginal sinu> 



tluur li*rtPI*4 which run in a from in 



front backwards ami also receive lateral branches from the vascular 

 network. From the himl part of the sinus ter minalis the blood is 

 taken up by the veiue vitellinse posteriores, of which the one of 

 left side is larger than the one of the right; the 



