144 THE STRUCTURE OF THE FOWL 



On the fifth day the embryo, lying on its 

 left side, is still very much curved. The 

 limb buds have elongated, and the position of 

 the elbow- and knee-joints is indicated. 



By the seventh day (Fig. 72) the cervical 

 flexure is almost absent, and there is a well- 

 defined neck. The eye is prominent, the mid- 

 brain produces less bulging on the summit of the 

 head, and the formation of a beak is recognis- 

 able. Development of viscera has resulted in 

 prominence of the abdomen. The limbs have 

 further elongated, and there are indications 

 of digits. 



On the eighth day (Fig. 73) the embryo is 

 more definitely bird-like. Papillae from which 

 the feathers will grow are clearly visible and 

 arranged along specific areas. The eyes are 

 very prominent ; but the mid-brain has almost 

 entirely ceased to cause a protrusion on the 

 summit of the head. 



By the tenth day the fore-limb has assumed 

 the characters of a wing, and the digits of the 

 foot are completely separated. 



Recognisable feathers have appeared by 

 the thirteenth day. 



Hatching. — The following is a brief account 

 of the process of hatching as described by von 



