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. 
Ses Sasi 
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: 
Lto 4. Cephalic; entering into the composition of the occipital region 
of the skull. 
5to 16. Prebrachial; “e., entering into the region between the wing 
and the skull. 
17 to 19. Brachial. 
20 to 25. Between wing and leg. 
