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aorta is always ventral to the gut and that the dorsal 

 aorta is always dorsal to the gut. In this section, how 

 many ventral aortae are there ? How many dorsal aortae ? 

 Dorsal to the dorsal aorta and to either side of the hind- 

 brain are the anterior cardinal veins. The one on the 

 right side is the right anterior cardinal vein and the one 

 on the left side is the left anterior cardinal vein. Where 

 is the notochord? 



Draw the section, color the different germ layers, and 

 label all the parts. 



(2) Through the Hind-brain showing the Auditory Vesicles 



Identify all the parts found in this section that are 

 foimd in the previous sections. Ventral to the fore-brain 

 and between it and the phaivTix is an evagination from 

 the roof of the oral pit, the hypophysis. What is its 

 relation to the brain? Describe the auditory vesicles. 



Draw the section, color the different germ layers, and label 

 all the parts. 



(3) Through the Posterior Portion of fee Heart 



The amnion encloses the embrj'o dorsally, but not 

 ventrally. WTiat part of the central nervous system is 

 here? The mesoblastic somites are no longer thickened 

 blocks of cells, but hare dififerentiated into a somewhat 

 thickened plate of cells, the myotome or muscle-plate, 

 and a mass of cells that are more or less loosely packed 

 together, the sclerotome. What is the size and shape of 

 the gut in this section? Notice the thickened walls of 



