216 EMBRYOLOGY 



Figs. 8, 9, 10, U. — Diagrammatie cross and lorigUudiiial sections through 

 embryo Chichs of different ages. 



Fig. 8. — Half of a cross section through an embryo Chick oj two days, after 



KOLLIKEE. 



The embi^onic body, in which the neural tube (iV), chorda (c/t), primitive 

 segment with its cavity {ush), primitive aorta (ao),and the fundament of the 

 primitive kidney (un) are to be seen, is marked off from the extra-embryonic 

 region of the germ-layers by the marginal groove {gr). The body-wall begins 

 to be developed, owing to the somatopleure having given rise to the lateral fold 

 (sf), the ridge of which is directed toward the yolk. External to it the lateral 

 fold of the amnion («»/) rises in an opposite direction. 



Fig. 9. — Cross section of an embryo Chich at the beginning of the thvrd day, 



after Kollikeb. 



The lateral folds (^sf) have grown farther downward, and have completed the 

 body-wall. The lateral folds of the amnion (saf) likewise have risen up farther 

 toward the back of the embryo. The splanchnopleure has folded in to 

 form the groove dr. The dotted line hn indicates the still broad dermal 

 umbilicus, the line dn that of the intestinal umbilicus. 



Fig. 10. — Cross section through the trunh of a five-days embryo CJiick in, the 

 region of the umbilicus, after Eemak. 



By an approximation of the lateral folds, the body-wall has been completely 

 formed up to the region enclosed by the line hn, in which the body-cavity still 

 possesses!, an opening, and communicates with the extra-embryonic portion of 

 the body-cavity. At the line hn, the dermal umbilicus, the body-wall bends 

 over into the folds of the amnion (af), which have grown over the back of the 

 embryo, and are about to fuse along their edges. At the dermal umbilicus 

 {d9i) the intestinal tube (d) passes over into the yolk-sac, which is not 

 represented. 



Fig. 11. — Diagrammatic longitudinal section through an embryo Chick. 



The head is already fully differentiated from the blastoderm by the process 

 of folding, the tail-portion is less completely separated ; the former encloses 

 the cephalic portion of the intestinal cavity (lid), which is in connection with 

 the yolk-sac by means of the anterior intestinal portal (v.dpf). The pelvic 

 portion of the intestinal cavity, which shows the first traces of the allantois 

 (,al), communicates backwards and above with the neural tube by means of the 

 neurenteric canal (en), and toward the yolk-sac by means of the posterior 

 intestinal portal (Ji.dpf). The head-end is already partly ensheathed by the 

 anterior amniotic fold (yaf), whei'eas at the tail-end the posterior amniotic fold 

 (Jiaf) is just beginning to be elevated. 



