Shape : The 48 hours chick embryo will show this shape ? (In mirror view). In this stage of development the head region shows prolific growth. Because of which the embryo shows this peculiar shape.
Flexure : In the head region bendings are seen. These bandings are called flexure. This bending is towards right and backwards. In 48 hrs. Chick embryo two flexures are seen. One is at the region of midbrain. Because of this fore and hind brain will become parallel. This is called cranial flexure.
' In the posterior region of brain a cervical flexure is formed. This
flexure turn the head towards right. This region will give neck of adult.
Torsion : The 24 hours chick embryo is flat. Its ventral surface is in contact with yolk. As the development proceeds the anterior end of embryo is turns towards right and hence the anterior part of embryo comes to lie on the left side of yolk. This twisting is called torsion. At the end of 48 hours chick twisting will reach the cervical flexure. It is nearly at 13th somite.
Brain : The brain, shows three regions. Fore brain shows telencephalon and diencephalon, the hind brain shows medulla oblongata.
Eye : The optic cup is two layered. Lens placode is started its development.
Ear : The invagination of optic vesicle is completed. It is connected to ectoderm by endolymphatic duct.
Alimentary canal : Fore gut reaches-1!/2 mm. length.
Heart: It is 5' shaped. It is tubular. !t has not developed chambers sets.
Blood vessels: From the anterior end of heart two ventral aortae will arise. They run backwards and travel as dorsal aortae.
Kidney: Pronephrous is completely developed. Mesonephric tubules started development.
Somites : At 48 hours of incubations 25 pairs are seen. Meso-nephric tubules will develop from intermediate mesoderm.