CONTENTS ix 



PAGE 



Visceral Pouches 307 



The Thymus 308 



Epithelial Vestiges 309 



The Posthranchial Bodies 309 



III. The (Esophagus, Stomach and Intestine .... 309 



(Esophagus 312 



Stomach 313 



Large Intestine, Cloaca, and Anus 314 



IV. The Development of the Liver and Pancreas . . . 319 



The Liver 319 



The Pancreas 323 



V. The Respiratory Tract 325 



Bronchi, Lungs and Air-sacs 325 



The Laryngotracheal Groove 331 



CHAPTER XL THE BODY-CAVITIES, MESENTERIES AND 



SEPTUM TRANSVERSUM 333 



I. The Separation of the Pericardial and Pleuroperi- 



TONEAL Cavities 333 



Septum Transversum 334 



Closure of the Dorsal Opening of the Pericardium . . . 337 



Establishment of Independent Pericardial Walls . . . 338 



Derivatives of the Septum Transversum 339 



II. Separation of Pleural and Peritoneal Cavities; Or- 



igin OF THE Septum Pleuro-peritoneale . . . 340 



III. The Mesenteries 342 



The Dorsal Mesentery 342 



The Origin of the Omentum 343 



Origin of the Spleen 345 



CHAPTER XIL THE LATER DEVELOPMENT OF THE 



VASCULAR SYSTEI\r 348 



I. The Heart 348 



The Development of the External Form of the Heart . \ 348 



Division of the Cavities of the Heart 350 



Fate of the Bulbus 357 



The Si7ius Venosus 357 



II. The Arterial System 358 



The Aortic Arches 358 



The Carotid Arch 361 



The Subclavian Artery 362 



The Aortic System 362 



