in order to make the following description more comprehensible , it is pointed out that the trocar comprises a body ( 1 ) equipped with a tip ( 2 ). the body comprises a tube ( 1b ) underneath a bell - mouthed part ( 1a ). part ( 1b ) is axially drilled at ( 1c ) over its entire length whereas part ( 2 ) has an internal through - channel ( 2a ). hole ( 1c ) and channel ( 2a ) are in coaxial alignment . the surgical instrument that is to be used is inserted through internal channel ( 2a ) in tip ( 2 ) so that it protrudes beyond the free end of body ( 1 ). bell - mouthed part ( 1a ) has an internal recess ( 1d ) that communicates with channel ( 2a ) and hole ( 1c ). this recess accommodates a swivel valve ( 3 ) of which the axis of rotation is situated in tip ( 2 ) and which is held in the shut - off position by spring ( 4 ). in the position where channel ( 2a ) and hole ( 1c ) are shut off , valve ( 3 ) rests against its seat ( 2b ) comprising a seal ( 2c ). valve ( 3 ) is retracted under the effect of inserting the instrument ; it can also be operated externally by simply exerting finger pressure on operating handle ( 3a ) if the operator needs to extract delicate &# 34 ; objects &# 34 ; from the organism during an intervention . according to one basic characteristic of the invention , tip ( 2 ) is fitted with internal features that can be operated externally and are capable of modifying the diameter of channel ( 2a ) in order to match it to the diameter of the instrument to be inserted . as will be shown in the rest of this description , these features are shaped in order to ensure leaktightness inside the trocar after the instrument is inserted . in the embodiment shown in fig1 to 4 , the features consist of a reducing adapter in the form of a hinged arm ( 5 ) actuated by lever ( 5b ). this arm ( 5 ) has at least one hole ( 5a ) of diameter less than that of channel ( 2a ) in tip ( 2 ). the arm is hinged at ( 5c ) so that it swivels angularly when force is exerted on lever ( 5b ) in order to line up holes ( 5a ) and ( 2a ) ( fig3 and 4 ). reducing adapter ( 5 ) is accommodated transversely a housing ( 2e ) formed in the thickness of tip ( 2 ). said housing ( 2e ) is designed either to coaxially align hole ( 5a ) with channel ( 2a ) ( fig3 ) or to completely free channel ( 2a ) ( fig1 and 2 ), depending on the angular position of lever ( 5b ). the axis of rotation ( 5c ) of reducing adapter ( 5 ) is parallel to the axis of the trocar . it is clear that , depending on the angular position of reducing adapter ( 5 ), it is possible to modify the diameter of the inlet of channel ( 2a ) in order to match it to the diameter of the instrument to be used . in order to ensure leaktightness , a seal ( 7 ) is fitted in the inlet of insertion channel ( 2a ) in tip ( 2 ) upstream from hinged arm ( 5 ) and downstream from valve ( 3 ). the effect of this seal ( 7 ) is to ensure leaktightness of the instrument whose diameter corresponds to that of channel ( 2a ), i . e . in the retracted position of reducing adapter ( 5 ) ( fig1 and 2 ). in order to ensure leaktightness in the case of an instrument of smaller diameter , i . e . when arm ( 5 ) is swivelled so that it lines up its hole ( 5a ) with hole ( 2a ) ( fig3 ), said hole ( 5a ) has an internal seal ( 6 ) capable of cooperating with the body of the corresponding instrument . note that disposable tip ( 2 ) is connected to body ( 1 ) by a click - on system comprising a seal ( 2d ) that ensures complete leaktightness between the two parts of the trocar . in addition , in order to make it possible to re - inflate or deflate the peritonium , the trocar is equipped with a slide valve ( 8 ) that is opened or closed by a quarter - turn cock ( 8a ). in another embodiment , the reducing adapter consists of a spherical plug ( 9 ) having at least two through - holes ( 9a ) ( 9b ). these holes are of different diameter and are capable of being axially aligned with channel ( 2a ) under the action of angular swivelling of lever ( 10 ). advantageously , plug ( 9 ) has two through - holes arranged in two orthogonal planes . hole ( 9a ) is of smaller diameter than channel ( 2a ) whereas the diameter of hole ( 9b ) is equal to the diameter of said channel . as previously , in order to ensure leaktightness after inserting the instrument , each hole ( 9a ) ( 9b ) has an internal seal ( 11 ). it is therefore sufficient to orientate the plug by actuating lever ( 10 ) in order to coaxially align either hole ( 9a ) ( fig5 and 6 ) or hole ( 9b ) ( fig7 and 8 ) with channel ( 2a ) depending on the diameter of the desired instrument . according to another characteristic , body ( 1 ) of the trocar has external annular peripheral ribs ( 1c ) over all or part of its length . the advantages are apparent from the description with special emphasis being placed on the following points : the facility to easily disassemble the tip and body of the trocar with a view to obtaining a disposable tip , the production of a compact , ergonomic trocar that includes , in its tip , a reducing adapter and a sealing valve that can be operated externally with one hand without having to release the trocar , the facility to modify the diameter of the insertion channel in the tip depending on the diameter of the instrument to be used , the facility to extract delicate &# 34 ; objects &# 34 ; during an intervention by manually retracting the sealing valve by using an external lever ,
trocar for inserting endoscopy instruments into cavities , the trocar having a cleanable hollow body , a disposable tip which is equipped with a swivel valve that can be retracted by inserting the instrument through an internal channel in the tip that communicates with the hollow body . the disposable tip is also equipped with externally operable features capable of modifying the diameter of channel in order to match it to the diameter of the instrument to be inserted .