3ß4 HIROTA ; ON THE SERO-AMNTOTIC CONNECTION, 



divided into two brnnrhes at the point Z (cf. Figs. 14 and 23), and 

 that the two branches ascend directly, along the free edges ZY and ZX, 

 townrds the outer limb. At this stage the albumen-sac has assumed a 

 peculiar elongated form, and the ' omhilic omhilicaV of Uuval, by which 

 the albumen-sac is united to the yolk-sac, has l)ecome conspicuous and 

 easily observable. The sac is supplied Avith numerous blood vessels on 

 the yolk side, and albumen is absorbed through that singular placental 

 structure discovered by Duval in the linnet. The position of the 

 umbilicus may vary in different individuals (Figs. 29 and 34), but 

 the papillatcd placental structure of the albumen sac is always con- 

 fined to the vicinity of the umbilicus. It is to be added that from 

 this staçfe the blood vessels of the outer allantoic limb undero-o certain 

 changes in their distribution. One Ijasal branch of the allantoic 

 vein, which runs with the right allantoic artery, becomes conspicuous 

 by anastomosing with other branches of the same vein (Figs. 27, 2(S, 

 32, and 33). 



On the eighteenth day, the albumen-sac appears as a slender tube 

 which opens into the amniotic cavity thnjugh the perforated connec- 

 tion (Figs. 32-35). Fig. 3(3 represents the septa come together at the 

 ])oint P as seen from the vegetable pole. [n this case the spot 

 where the riofht allantoic artery divides is concealed beneath the 

 yolk-sac, and the two branches ascend along the free edges ZX 

 and ZZ'Y respectively towards the outer allantoic limb. In this 

 example the primary interallantoic septum has iKjt l)een folded along 

 an axis in the allantoic cavity (cf. Diag. 1), lî), and moreover is not 

 influenced by the left allantoic artery. 



At length, the albumen becomes entirely absorbed and the vitel- 

 line membrane which had previously been imbedded in albumen 

 is alone left in the former albumen-sac, often partly ])rojected into 

 the amniotic cavity through openings in the sero-amniotic connec- 



