MEDIAN SAGITTAL DISSECTIONS 



141 



a short time, and are invaluable in giving one an idea of the form, positions, and relations of 

 the different organs. By comparing the early (Figs. 96 and 122) with the later stages (Figs. 

 146 and 147) a number of interesting points may be noted. 



Isthmus Mesencephalon 



M cti:ih:cpha!oii 



Chorioiil pUxiis of Jmirlli '.nilridc 



11 y po p li ys i s 



Tela chorioidea imirili vcii/riiU' 

 Myelenceplmlon 



Epiglollis 



Third iriilrii'li' 



Dicnccpliiiton 



Coy pus \!riatii.m 



Cerebrum 



Notocliord 



Trachea 



Trunk pulm. artery 



Wall of atrium 



Foramen ovate 



Esophagus 



Lung 



Dorsal aorta 



Stomach 



Intersegmental 

 arteries 



Paucrec 



Common bile duet 

 Dnodcn 



nital sinus 



Mesonephric duct 



Rcclmn 



Ureter 



Fig. 146. — Median sagittal dissection of an 18 mm. pig embryo, showing central nervous system in 

 section and the viscera in position. X 8. 



In the brain, the corpus striatum develops in the floor of the cerebral hemi- 

 spheres. The interventricular foramen is narrowed to a slit. In the roof of the 

 diencephalon appears the anlage of the epiphysis, or pineal gland, and the chorioid 

 plexus of the third ventricle. This extends into the lateral ventricles as the 



