AXD THE FOETAL MEMBRANES, IN THE CHICK. ßfj^ 



(Figs. 23 and 25) : the allantoic vein and the Jeit allantoic artery on 

 one side and the right allantoic artei-v on the other (Z, Fig. 25). The 

 allantoic vein passes towards the right along the inner limh (Fig. 28) 

 to the point marked F on Fig. 25, then passes from the inner to the 

 outer limh along the line between F (Fig. 23) and E (Fig. 24)* 

 (like the line FE, Fig. 15) and emerges on the outer limb at the 

 point E (Figs. 22 & 24). The full line EG corresponds to the 

 line EM in Fig. 15 and the fold FEOMF to the fold FECMDF in 

 Fig. 15. The right allantoic ;u"tei-y stîu-ting from the point Z (Fig. 

 25) runs towards the left, but soon divides mainly into two branches 

 (Fig. 23), each of which together with a third smaller one produces 

 a fold in the allantois thus making three minor septa. No septum 

 formed by the terminal portion of the left allantoic artery is present in 

 tliis case. All the septa above referred to come together at the point 

 marked (Fig. 24). Fig. 2() represents the allantoic septa which have 

 thus come together, as seen from tlie vegetable pole. Full lines show 

 the tracings of these septa on the outer limb of the allantois. In 

 addition to the |)i-imary interallantoic septum (E'O) there are tliree 

 minor sej)ta. formed by three branches of the right allantoic artery 

 which run along the free edges ZX, ZY, and MN. Notice also how 

 the albumen-sac, now pit(;her-sliaped, has decreased in size. 



l)y the sixteenth day yolk, as well as albumen, is much reduced in 

 volume and the princi])al part of the e^xg is now the amni(^n occupied 

 by the embryo proper (Figs. 27-30). Fig. 31 represents the septa (only 

 three in all in this case) come together at the point F, as seen from the 

 vegetable pole. In this figure we see that the right allantoic artery is 



* The reiider will understand that in tracing a bloodvessel or other structure from the 

 surface rejj resented in Figs. 23 and 25 to that given in Figs. 22 and 24, the upper edge of the 

 former two figures should 1)P applied to the lower edge of the latter two figures and also that as 

 eggs have a considerable thickness, a structure leaving one surface may not l)e found at exactly 

 the corresponding point of the other. 



