592 



Z( )( )LOGY 



around the embryo, and grow upwards and inwards, eventually 

 meeting in the middle over the body of tlie embryo, and 

 uniting in such a way as to form two layers. Of the two layers 

 thus formed the outer, consisting of trophoblastic ectoderm and 

 somatic mesoderm, simply constitutes a joart of the extra- 

 embryonic somatopleure which forms a comj^lete investment for 



Vir.. 1-210.— A Rabbit embryo and blastodermic vesicle at the end of the tenth day. The 

 embryo is represented in surface view from the right side, the course of the alimentary 

 canal Ijeiug indicated )iy the broad dotted line ; the blastodermic vesicle is shown in median 

 longitudinal section. The greater jiart of the tail has been removed. AN', pro-amniou ; 

 .I.Y, cavity of amnion; C. extra-embryonic portion of cielonio : E. ectoderm; 7/. thickened 

 ectoderm by wliieli the vesicle is attached to the utcru.s and from which the fietal part 

 of the placental is derived ; Ear. ectodermal villi ; El. auditory vesicle ; EK, ectuderiual 

 villi; OF. fore-gut; OH. hind-gut; GT. mid-gut; H. endoderm ; OL. lens of eye ; R. heart; 

 81. sinus ternnnali.s; TA. allantoic cavity ; YS. yolk-sac. (From Marshall, in i.art after Van 

 Beneden and .Julin. ) 



tlie entire sphere, and is known as the chorion (Fig. 1218, 2 and 3). 



In the account of the development of the Bird it has been 



referred to as tlie false amnion or scroti.^ nicmhranc. The inner 



amnion, as in the Bird, forms the wall of a cavity— 



'acitii (4 and 5, (^A)— which becomes tensely filled 



with tiuid {ihG liquor (imnii) over tlic body of the embryo; this 



layer or true 



the aniiLioia 



serves the purpose of protecting the delicate embryo fi 



ryo ; 



0111 



the 



