Nipple for nursing bottle

A nipple for nursing bottles, comprising:

• a nipple body having a pair of openings provided at front and bottom ends thereof and including an inverted funnel-shaped intermediate portion;
• at least one air valve slit provided in a vicinity of said bottom end for communicating an inside portion of said nipple to an outside portion thereof;
• and
• a partition diaphragm provided inside of said nipple body and integral thereto and disposed in a region remote from said front and bottom ends of the nipple body in a vicinity of a boundary between said front end and said inverted funnel-shaped intermediate portion and at a position where external pressure is exerted by a mouth of an infant during feeding, said partition diaphragm including a spherical recess at a central portion thereof defining a thin diaphragm portion thereat such that said partition diaphragm is easily deformable particularly at said thin diaphragm portion,
• wherein said partition diaphragm has a cut through said thin diaphragm portion and forms a milk sucking passage therein, said cut being normally closed,
• wherein said cut is opened only when said partition diaphragm is deformed in response to said external pressure exerted by a mouth of an infant upon said nipple body during feeding.