MEDIAN SAGITTAL DISSECTIONS 



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

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

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



Isthmus Mcsencephalon 

 Metencephalon 



Chorioid plexus of fourth ventricle 

 Hypophysis \ 



TV/a chorioidea of fourth ventricle 

 Myelencephalon 



Epiglottis 



Third ventricle 



Diencephalon 



Corpus slrialum 



Cerebrum 



Wall of atrium 



Foramen male 



Esophagus 



Lung 



Dorsal aorta 



Stomach 



Inlersegmental 

 arteries 



Pancreas 



Common bile duel 



Duodenum 



Urogenital sinus 

 Rectum 



Genital fold 



Mctanepkros 



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. 



