EVOLUTION OP THE CHICK. 



149 



tute vessels, the trunks of which become attached 

 to the chick. Haller says, we can now perceive 

 traces of the back-bone (vertebrce), like small glo- 

 bules, disposed on the two sides of the middle of the 

 spine, the wings and the blood-vessels of the navel, 

 distinguished by their dull colour, also beginning to 

 appear. The neck and breast are unfolded, the head 

 is enlarged, the outlines of the eyes and their three 

 surrounding coats now become perceptible, and the 

 heart is seen pulsating and the blood circulating. 



An Egg as it appears thirty-six hours after incubation, with a magnified 

 view of the Embryo Chick. 



Blumenbach does not mention his having seen the 

 heart before the commencement of the third day, 

 when it resembles a tortuous canal, and consists of 

 three dilatations lying close together and arranged 

 in a triangle, one part of which is properly the right 

 auricle, forming at this period a common auricle, 

 and another is the only ventricle, which afterwards 



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