THE ANATOMY OF TEN TO TWELVE MM. PIG EMBRYOS 



125 



see p. 158.) The pharyngeal pouches are now larger than in the 6 mm. pig (Fig. 

 1 1 8). The first pouch persists as the Eustachian tube and middle ear cavity, 

 the closing plate between it and the first branchial cleft forming the tympanic 

 membrane. The second pouch later largely disappears. About it, develops the 

 palatine tonsil. The third pouch is tubular, directed at right angles to the pharynx 



Metencephalon 

 Tela choroidea 



Neuromeres of myelencephalon 



Notochord 

 Tongue 



Spinal cord 



Dorsal Pancreas 



Hepatic diverticulum " 

 Duodenum 



L. genital fold 



L. mesonephros 



Dorsal aorta 



Colon 

 Umbilical artery (cut away) 



Metanephros 



Mesencephalon 



Diencephalon 



Post, lobe hypophysis 



Optic recess 



Telencephalon 



Ant. lobe hypophysis 



Bulbils cordis 

 Ventricle 

 Yolk-sac 



Septum transversum 

 Yolk-stalk 

 Liver 



Caecum 



'mall intestine 

 'Allantois 

 Urogenital sinus 



Ureter 

 Mesonephric duct 



Rectum 



? IG. 117. Median sagittal dissection of a 10 mm. pig embryo, showing the brain, spinal cord and viscera 



from the right side. X 10.5. 



and meets the ectoderm to form a "closing plate." Median to the plate, the 

 ventral diverticulum of the third pouch is the anlage of the thymus gland. Its 

 dorsal diverticulum forms an epithelial body, or parathyreoid. The fourth 

 pouch is smaller and its dorsal diverticulum gives rise to a second parathyreoid 

 body. Its ventral diverticulum is a rudimentary thymus anlage. A tubular 



