EXTRA - EMBRYONIC TISSUE_ 



FOREGUT-f- I 



ANTERIOR 

 NTESTINAL 

 5 PORTAL 



MIDGUT- 



NOTOCHORD - 



NEURAL- 



5 ECTODERM !| 



■ 'F 



II POSTERIOR it 



INTESTINAL 



PORTAL 



A —^. ^ '.V 



ANTERIOR NEUROPORE 



CAUDAL FOLD OF AMNION 

 ANTERIOR NEUROPORE 



Fig. 242. Early development of the pig embryo (B, C, and G from Patten: Embryology 

 of the Pig, Philadelphia, Blakiston; A is from Streeter: Carnegie Inst. Publ. No. 380, 

 Contrib.' to Embryol. 100; D, E, and F from Heuser and Streeter: Carnegie Inst. Publ. 

 No. 394, Contrib. to Embryol. 109. All figures have been modified). (A) Early, neural 

 groove stage. Neural area is shown in black; amnion is cut away as indicated. (B) 

 Four-somite stage. (C) Median sagittal section, approximating the stage of develop- 

 ment shown in (B). Observe foregut, midgut, and hindgut areas. (D) Embryo of about 

 six pairs of somites. (E) Embryo of about 7 to 8 pairs of somites. (F) Eighteen 

 pairs of somites. (G) Sagittal sectional diagram of embryo slightly younger than (F), 

 showing neural and gut tubes, amnion, allantois, and forming heart. 



496 



