ii8 



COMPARATR'E ANATOMY 



and 87) thus leaving the greater part of the inner surface of the shell 

 membrane free to make close contact with the vascular and respiratory 

 chorio-allantoic membrane. The now localized remnant of albumen is 

 gradually absorbed by the embryonic layers adjacent to it. 



ectoderm 

 neural tube 



sero-amniotic cavity 

 hind- gut 



proctodaeum 



amniotic cavity 



netiral tube 

 notochord 



post-anal 

 gut 



Fig. 88. — Diagrams representing median longitudinal sections of the caudal region 

 of chick embryos. A, after about three days incubation; B, after about four days 

 incubation. (From Patten, Embryology of the Chick.) 



Before the time of hatching the shrinking yolk-sac is drawn up into 

 the growing body. The umbilical stalk — that is, the whole complex of 

 connections between the definitive body of the embryo and the extra- 

 embryonic membranes — becomes narrowly constricted. At time of 



