MEDIAN SAGITTAL DISSECTIONS 



143 



This extends into the lateral ventricles as the lateral chorioid plexus. The dorso-lateral 

 wall of the diencephalon thickens to form the thalamus, and the third ventricle is narrowed 

 to a vertical slit. The increased size of the cerebellum has been noted. Into the thin dorsal 



Isthmus M esencephalon 

 Metencephalon 



Chorioid plexus of fourth ventricle 

 Hypophysis 



Tela chorioidea of fourth ventricle 

 Myelencephalon 



Epiglottis 



Intersegmental 

 arteries 



Pancreas 



Common bile duel 



Duodenum 



Third ventricle 



Diencephalon 



Corpus striatum 



Cerebrum 



\ Small intestine 

 Allantois 

 Bladder 

 'Phallus 







Urogenital sinus 



Rectum 



Genital fold 



Metanephros 



Mesonephric duct Ureter 



FIG. 146. Median sagittal dissection of an 18 mm. pig embryo, showing the brain in section 

 and the viscera in position. X 8. 



wall of the myelencephalon grows the network of vessels that forms the chorioid plexus 

 of the fourth ventricle, which is now spread out laterally and flattened dorso-ventrally. 

 About the notochord, mesenchymal anlages which form the centra of the vertebra are 

 prominent. 



