A mammary crest usually stops growing at 8 weeks and its length is regressed starting at the caudal end and extending cranially, so that what remains is a round, ectodermic placode where the axilla develops.
12.
During the invagination of the optic cup, the ectoderm begins to thicken and form the lens placode, which eventually separates from the ectoderm to form the lens vesicle at the open end of the optic cup.
13.
The GnRH neurones originate in an area of the developing brain called the olfactory placode; they then pass through the cribriform plate and into a structure called the olfactory bulb, where the sense of smell is generated.
14.
The lens placode is affected by the chordamesoderm making it to invaginate and forms the optic cup composed by an outer layer of neural retina and inner layer the pigmented retina that will unite and form the optic stalk.
15.
The term " placode " or " ectodermal placode " is sometimes used to refer specifically to cranial or neurogenic placodes, but is also used for areas of the ectoderm that give rise to structures such as mammary glands, feathers and hair.
16.
The term " placode " or " ectodermal placode " is sometimes used to refer specifically to cranial or neurogenic placodes, but is also used for areas of the ectoderm that give rise to structures such as mammary glands, feathers and hair.
