184 



THE DEVELOPMENT OF THE CHICK 



figures of entire embryos. The formation of new somites con- 

 tinues after the end of the period discussed in this chapter, 

 up to about the sixth day. Each somite has a definite value in 

 the developmental history. 



tot 



A.V. 



-i 







FIG. 106. The same embryo from beneath, x 10. 



a. i. p., Anterior intestinal portal. A. V., Vitelline artery. 

 Int., Intestinal groove. 



In an embryo of 42 somites (about ninety-six hours), the value of 

 the somites as determined by their relations and subsequent history 

 is as follows: 

 1 to 4. Cephalic ; entering into the composition of the occipital region 



of the skull. 

 5 to 16. Prebrachial; i.e., entering into the region between the wing 



and the skull. 

 17 to 19. Brachial. 

 20 to 25. Between wing and leg. 



