60 



THE EARLY DEVELOPMENT OF MAMMALS. 



The fore-gut in the 4.2 mm. embryo has lengthened. It communicates freely 

 with the oral cavity proper, the limit of which is indicated by the hypophysis, Hy, 

 which is of ectodermal origin. The cephalic portion of the canal has undergone a 



FIG. 27.- OUTLINES OF THE NOTOCHORD AND ENTODERMAL CANAL OF THREE HUMAN EMBRYOS. A, 4.2 MM. 



B, 7.0 MM. C, 13. 8 MM. 



Al, Allantois. Ch, Notochord. Col, Large intestine. E, Caudal intestine. Ep, Epiglottis. Hy, Hypophysis. 

 in, Small intestine. La, Larynx. Li, Liver. Li.d, Hepatic duct. Lu, Lung. Md, Mandible. N, Renal 

 anlage. ?, (Esophagus. P, Dorsal pancreas. St, Stomach. T, Tongue. Th, Thyroid gland. Ur, 

 Ureter. W, Wolffian duct. Yk.s, Yolk-sac. 1,2,3, nrst > second, and third gill- pouches. Xi2diams. 

 (After W. His.) 



great widening to form the pharynx, with its characteristic gill-pouches (Fig. 27, A, 

 i, 2, 3) compare below. From the caudad end of the pharynx, the anlage, Lu, of 

 the trachea and lungs has appeared on the ventral side. From the pulmonary an- 



