ESOPHAGUS, STOMACH AND INTESTINE 



173 



umbilical cord into the abdominal cavity through a rather small aperture; the 

 ccelom of the cord is soon after obliterated. 



In embryos between 10 and 30 mm., vacuoles appear in the wall of the duodenum and 

 epithelial septa completely block the lumen. The remainder of the small intestine remains 

 open, although vacuoles form in its epithelium. Villi appear as rounded elevations of the 

 epithelium at 23 mm. (Johnson). They begin to form at the cephalic end of the jejunum, and 

 at 130 mm. (C R) they are found throughout the small intestine (Berry). Intestinal glands 

 appear as ingrowths of the epithelium about the bases of the viUi. They develop first in the 

 duodenum at 91 mm. (C R). The duodenal glands (of Brunner) are said to appear during the 



Braiji 



Tip of tongue 

 Thyreoid gland 



Pericardium 

 Gall bladder 



Small iiilesline 



Cacum 



Hypophysis 



\^ Foramen cacum 

 Root of tongue 



Esophagus 



Trachea 

 Notochord 

 Spinal cord 



Urogenital sl)ius 

 Anal membrane 



Rectum 



Fig. 180. — Diagrammatic median sagittal section of a 17 mm. human embryo, showing the digestive canal 



(modified after Mall). X 5. 



fourth month (Brand). In embryos of 10 to 12.5 mm. the circular muscle layer of the intes- 

 tine first forms. The longitudinal muscle layer is not distinct until 75 mm. (C R). 



The impervious duodenum of the embryo may persist as a congenital anomaly, and 

 the persistence of the yolk stalk, as Meckel's diverticulum, has already been mentioned (p. 171). 



The large intestine, as seen in 9 mm. embryos (Fig. 179), forms a tube extend- 

 ing from the cacum to the cloaca. It does not lengthen so rapidly as the small 

 intestine, and, when the intestine is withdrawp from the umbilical cord (at 

 42 mm. C R), its cranial or caecal end lies on the right side and dorsal to the small 

 intestine (Fig. 181). It extends transversely to the left side as the transverse 



