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. 

 118). 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 



^Telencephalon Mesencephalon 

 Tela choroidea 

 Neuromeres of myclcncephalon 



Kolochord 

 Tongue 



Spinal cord 



Dorsal Pancreas 



Ilepalic diverticulum 



Duodenum 



L. genital fold 



L. mesonephros 



Diencephalon 



Post, lobe hypophysis 



Optic recess 



Telencephalon 



Aid. lobe hypophysis 



ulbus cordis 

 Venlriele 

 Yolk-sac 



Septum transversum 

 Yolk-stalk 

 Liver 



Carum 



'Small intestine 

 'Allanlois 

 Urogenital sinus 



Ureter 

 Mesonephric duct 



Dorsal aorta 



Colon 

 Umbilical artery (cut away) 



Me/auephros Rectum 



Fig. 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 parathyrcoid. 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 



