CHICK, 68 TO 72 HOURS' INCUBATION 29 



Draw the seventy-two-hour whole mount and label all 

 the parts. 



b. Transverse Sections 



Study your sections and on your drawing of the whole 

 mount indicate the angle at which they have been cut. 



1 i) Through the Auditory Vesicle 



This section passes through the body twice. Why? 

 Are the two parts of the body separate or continuous? 

 What portions of the central nervous system are shown 

 in each part? What blood vessels are seen in this 

 section? If you cannot tell by looking at only the one 

 section, trace them through and compare with the blood 

 vessels in your sections of the forty-eight-hour chick. 

 Between the floor of the hind-brain and auditory vesicle 

 may be seen the ganglion complex of the seventh and 

 eighth cranial nerves, the acustico-facialis ganglion. 

 Above the third aortic arch and ventral to the auditory 

 vesicle is the ganglion of the ninth cranial nerve, the 

 glosso-pharyngeal ganglion. 



Draw the section, color the different germ layers, and 

 label all parts. 



(2) Through the Optic Vesicle 



Your section should be selected so that it will show, if 

 possible, the choroid fissure, the lens, and the optic stalk. 

 What part of the fore-brain is in your section? A part 

 of the hind-brain also may be in the section. What 

 is the relative position of the different parts of the brain ? 



