152 secured at one end to the fixed part 104 and hinged at the other end at 153 to arms 154 extending from the cross members 108 and 108a the use of the illustrated bed 101 is analogous to that of the bed shown in fig1 and 2 and will therefore not be further described fig5 and 6 show a further embodiment of the bed of the preceding figures in these figures parts equal to those described with reference to fig1 to 3 are indicated by the same reference numerals plus 200 in fig5 and 6 each element 205 is moved by an articulated parallelogram system 270 in particular the support bar 210 for each mobile element 205 forms one of the sides of the articulated parallelogram this bar comprises projections to which a further two sides 273 of the parallelogram 270 are hinged at 272 the sides 273 are hinged at 274 to projections 275 extending from the cross members 208 and 208a of the bed 201 in positions corresponding with each mobile element 205 and are hinged at 276 to the other side 277 of the articulated parallelogram in the embodiment shown in fig5 on one of said two sides 273 there acts a connecting rod 280 operated by a crank 281 rotated by an electric motor 282 for example of the direct current and advantageously stepping type this motor is fixed to a cross member 283 parallel to the upper cross member 208a and located between this latter and the floor on which the bed 201 rests in contrast in fig6 each articulated parallelogram 270 is moved manually for this purpose on one of the two sides 273 of each articulated parallelogram there acts an arm 290 hinged at 291 to said side 273 and at.