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CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This patent application claims the benefit of U.S. Provisional Patent Application No. 60/639,895, filed Dec. 22, 2004, the disclosure and teachings of which are incorporated herein in their entireties. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to devices which allow pets, such as dogs, to ascend to and descend from elevated surfaces, such as truck beds, vehicle interiors, or tables used for veterinary or grooming services, under their power without the need for jumping or being lifted, and more particularly to a foldable staircase for use by pets.  
       BACKGROUND OF THE INVENTION  
       [0003]     There is a need for a device that allows pets, such as large dogs, to walk up to and down from elevated surfaces, so that the pet is not required to risk injury while jumping up to or down from the elevated surface, and so that a pet owner or handler is not required to risk injury to either the pet or himself/herself in attempting to lift the pet up to or down from the elevated surface. It is also desirable that the device be lightweight, and collapsible to a compact folded size so that it may be easily transported and handled by persons carrying or setting up the device. It is further desirable that the device be capable of quick adjustment to operate between surfaces that are located at various heights from one another.  
         [0004]     Prior devices involving fixed or folding ramps do not work well for use in meeting the above described needs for several reasons. First, pets such as dogs have difficulty in walking down a ramp, and tend to walk off the edge of the ramp, because they cannot see the ramp below them. The angle of ascent/descent of a ramp which can be readily negotiated by the pet must typically be rather shallow, making the ramp too long to be useable in tight spaces, and difficult to stow, particularly if the ramp is not foldable to less than its fully extended length.  
         [0005]     Experience has shown that devices using steps work better than devices using ramps, because pets become acclimated to negotiating steps during day-to-day activities. Experience has also shown that pets can easily negotiate substantially steeper angles of ascent and descent while using staircase-type devices. The steeper angle of ascent and descent and construction of staircase-type devices also helps pets to ascend or descend, without walking off of the edges of the steps, because the animal can see the steps above and below them, while ascending or descending, more readily than they can see a ramp surface. The greater angle of ascent/descent also allows a device using steps to be shorter than a ramp would be for a given difference in elevation between the elevated surface and the floor or ground.  
         [0006]     Prior devices using steps, however, whether rigid or folding, fall short of meeting the needs and desirable attributes described above. It is desirable, therefore, to provide an improved apparatus and method for allowing pets to ascend to and descend from an elevated surface, in a manner that better fulfills one or more of the needs and desirable attributes described above.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The invention provides an improved method and apparatus for allowing pets to ascend to and descend thereupon, through use of a foldable staircase having stair treads operatively connected by articulating links in such a manner that the treads can be pivoted in unison from a stowed position of the staircase, in which the treads are substantially stacked upon one another, to a plurality of extended positions, in which the links position the treads in a spaced and parallel relationship to one another. The foldable staircase may also include a latch for selectively securing the staircase in a selected one of the extended positions. The latch may be configured for preventing further pivoting, once engaged, of the treads in either or both directions between the stowed and extended positions of the staircase.  
         [0008]     The treads and articulating links may be configured so that in a fully extended position, the treads form a relatively flat surface, thereby allowing the staircase in the fully extended position to be used as a litter, or stretcher, for transporting a person or an animal. The staircase may also be configured so that the links may be removed and used as splints for stabilizing fractured bones. Where the staircase includes a latch, the latch may be configured for selective disconnection, so that the staircase may be pivoted to the fully extended position only when the latch is disconnected. Alternatively, the latch may be configured for selectively locking the staircase in the fully extended position.  
         [0009]     A foldable staircase, according to the invention, may also include a covering for one or more of the treads, such as carpeting or rubber matting. Alternatively, the upper surface of the tread may include an integrally formed non-slip surface.  
         [0010]     A foldable staircase, according to the invention, may further include a non-slip element on the underside of one or both of a top and a bottom tread of the staircase. The non-slip element may take many forms, such as a plurality of buttons of a resilient material such as rubber, or a strip or sheet of resilient material attached to the underside of the top and/or bottom tread.  
         [0011]     One or more of the treads may include hand-holds for facilitating pivoting the staircase between the stowed position and extended positions. The staircase may be constructed of waterproof or moisture tolerant materials, such as plastic, stainless steel, aluminum, or plated metal, so that the staircase can be used in wet conditions, or for entry into, or egress from, a boat or other watercraft. The treads may also include openings therein for passage of water from a top surface to a bottom surface of the tread.  
         [0012]     In one form of the invention, a foldable staircase includes a plurality of treads having opposite side surfaces thereof joined by articulating links that are operatively connected to and disposed adjacently outward from the opposite side surfaces. The staircase may include a top tread, a bottom tread, and one or more intermediate treads, with each tread including three attachment points for the articulating links disposed along the opposite sides, with each tread including a front tread attachment point disposed adjacent the front edge of the tread, a rear tread attachment point disposed adjacent the rear edge of the tread, and an intermediate tread attachment point disposed substantially halfway between the front and rear tread attachment points along each of the opposite edges of the tread.  
         [0013]     The intermediate treads are attached to one another, and to the top and bottom treads, by pairs of long links having an intermediate long link connection point pivotably attached to the intermediate tread attachment points of a given intermediate tread, and upper and lower long link connection points disposed at opposite axial ends of the long links. The upper long link connection points are pivotably connected to the front tread attachment points of either the top tread, or another adjacent intermediate tread disposed above the given intermediate tread. The lower long link connection points are attached to the rear tread attachment points of either the bottom tread or another adjacent intermediate tread disposed below the given intermediate tread.  
         [0014]     The top tread is further pivotably connected to an adjacent intermediate tread below by a pair of short articulating links. Specifically, the short articulating links each include an upper short link connection point pivotably connected to the intermediate tread attachment point of the top tread, and a lower short link connection point pivotably connected to the rear tread attachment point of the intermediate tread below and adjacent the top step.  
         [0015]     In similar fashion, the bottom tread is further pivotably connected to an adjacent intermediate tread above the bottom tread by a second pair of the short articulating links. Specifically, the second pair of short articulating links each include a lower short link connection point pivotably connected to the intermediate tread attachment point of the bottom tread, and an upper short link connection point pivotably connected to the front tread attachment point of the intermediate tread above and adjacent the bottom step.  
         [0016]     A foldable staircase, according to the invention, may include one or more latches, which when engaged, secure the staircase in a selected one of the extended positions. When engaged, the latch, or latches, may preclude further pivoting of the articulating links. A latch, or latches, according to the invention, may be operatively connected, at opposite ends thereof, to the intermediate attachment points of two adjacent treads.  
         [0017]     In one form of the invention, a foldable staircase may include a pair of latches each having an elongated body including a first end pivotably connected to one of the front tread attachment points of the bottom tread. The body of the latches may also define an elongated slot, extending along a longitudinal axis of the latch, for sliding receipt therein of a pivot member extending outward from a short link mid-link connection point. The slot further includes a series of notches therein for engaging the pivot member to prevent further pivoting of the treads between the stowed and extended positions, to thereby lock the staircase into rigid structure at a selected one of the extended positions.  
         [0018]     In some forms of the invention, the pivot member may be selectively disengaged from the short link arm attached to the lower tread, to thereby allow the staircase to be pivoted to the fully extended position for use as a litter or stretcher.  
         [0019]     The short articulating links may have a length between the upper and lower short link connection points that is substantially equal to the length between the intermediate long link connection point and both the upper and lower long link connection points of the long articulating links. It may also be desirable, for economy of manufacturing, to have identical short links connecting the top and bottom treads to the intermediate treads, with all short links including the mid-link connection point for receiving the pivot member.  
         [0020]     The short and long articulating links may be pivotably attached to the treads by threaded fasteners, such as shoulder bolts, which provide a controlled clearance fit to facilitate articulation of the links with respect to the treads. The pivot member may include a clevis pin extending through the short link attached to the bottom tread and the slot in the latch, and held in place by a cotter pin extending through a cross-drilled hole in the end of the clevis pin. A washer may be provided inboard of the nuts on the links and/or the cotter pin, to spread contact loads into the links, the latches and the treads.  
         [0021]     In another form of the invention, a foldable staircase apparatus is provided, which includes a foldable staircase, as described above, and a staircase holder adapted for receiving the staircase in the stowed position. The holder may be adapted for attachment to a surface, such as the tailgate of a truck or a sport utility vehicle, or a trunk lid of a vehicle.  
         [0022]     A foldable staircase apparatus, according to the invention may also include a foldable staircase, as described above, and a mounting bracket for pivotably attaching the staircase to a vehicle, a watercraft, or a table, so that the staircase may be pivoted about the mounting bracket in either or both of the stowed and extended positions of the staircase.  
         [0023]     An apparatus, according to the invention, may also take the form of a kit including one or more additional treads, and additional intermediate links and connection hardware for increasing the number of treads in the staircase so that the staircase can be used to allow the pet to ascend or descend greater distances while traversing the staircase.  
         [0024]     The treads of a staircase, according to the invention, may also be configured to have a great enough depth, between the front and rear edges thereof, so that a pet ascending the staircase cannot see an open space between the treads.  
         [0025]     The invention may also take the form of a method for constructing a foldable staircase, according to the invention, or a method for using a foldable staircase in a manner in accordance with the invention.  
         [0026]     Other aspects, objectives and advantages of the invention will become more apparent from the following description of the invention, in conjunction with the accompanying drawings.  
         [0027]     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:  
         [0029]      FIG. 1  is a perspective exploded view of a first exemplary embodiment of a foldable staircase, according to the invention, having four treads and a pair of latches for selectively securing the staircase in one of several extended positions.  
         [0030]      FIG. 2  is a right side view of the foldable staircase of  FIG. 1 , latched in the highest extended position.  
         [0031]      FIG. 3  is right side view of the foldable staircase of  FIG. 1 , latched in a lowest extended position;  
         [0032]      FIG. 4  is right side view of the foldable staircase of  FIG. 1 , in a fully extended position, with the latch disconnected.  
         [0033]     FIGS.  5 A-C are front, right side and bottom views, respectively of the foldable staircase of  FIG. 1 , in a stowed position.  
         [0034]      FIG. 6  is a right side view of a second exemplary embodiment of a foldable staircase, according to the invention, having five treads, but otherwise identical to the embodiment of  FIGS. 1-5C , with the foldable staircase latched in the highest extended position.  
         [0035]      FIG. 7  is right side view of the foldable staircase of  FIG. 6 , latched in a lowest extended position;  
         [0036]      FIGS. 8A and 8B  are front, right side views, respectively of the foldable staircase of  FIG. 6 , in a stowed position.  
         [0037]      FIG. 9  is an enlarged right side view of a latch of the foldable staircases of  FIGS. 1-8B .  
         [0038]      FIGS. 10 and 11  are bottom and cross sectional views respectively, of the treads of the foldable staircases of  FIGS. 1-9 .  
         [0039]      FIGS. 12-15  are enlarged cross-sectional views showing connections between the components of the foldable staircases of  FIGS. 1-8B , taken along lines as indicated in  FIG. 2 .  
         [0040]      FIG. 16  is an alternate embodiment of a latch, for a foldable staircase, according to the invention.  
         [0041]      FIG. 17  is a perspective view of an alternate exemplary embodiment of a foldable staircase, according to the invention, showing a second exemplary embodiment of a latch, according to the invention.  
         [0042]      FIGS. 18-21  are enlarged perspective illustrations of a portion of the latch, of the embodiment shown in  FIG. 17 , illustrating various details of the construction and operation of alternate embodiments of the latch shown in  FIG. 17 .  
         [0043]      FIG. 22  is an exemplary embodiment of a foldable staircase apparatus, according to the invention, including a foldable staircase and a holder for receiving the staircase in a stowed position.  
         [0044]      FIG. 23  is an exemplary embodiment of a foldable staircase apparatus, according to the invention, including a foldable staircase and a mounting bracket adapted for attachment to the top step of the staircase.  
         [0045]      FIG. 24  shows an exemplary embodiment of the invention, having a foldable staircase pivotably attached by a mounting bracket to a watercraft.  
         [0046]      FIG. 25  shows an exemplary embodiment of the invention having a foldable staircase and a mounting bracket for clamping the foldable staircase to a ladder of the type extending over the edge of a watercraft, or positioned along the edge of a swimming pool, pier, or dock. 
     
    
       [0047]     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0048]      FIG. 1  shows a first exemplary embodiment of the invention, in the form of a foldable staircase  100  including a plurality of treads  102 ,  104 ,  106 ,  108  having opposite side surfaces thereof joined by articulating links  110 ,  112  that are operatively connected to and disposed adjacently outward from the opposite side surfaces of the treads  102 ,  104 ,  106 ,  108 . Specifically, the staircase  10  includes a top tread  102 , a bottom tread  104 , an upper intermediate tread  106  and a lower intermediate tread  108 . It will be noted that all of the treads  102 ,  104 ,  106 ,  108  of the exemplary embodiment are identical, but this is not a requirement of the invention. It will further be noted that all of the treads  102 ,  104 ,  106 ,  108  include a carpet piece  105  attached to the upper surface of the treads  102 ,  104 ,  106 ,  108 , but other embodiments of the invention may use different treatments of the top surfaces of the treads  102 ,  104 ,  106 ,  108 .  
         [0049]     Each tread  102 ,  104 ,  106 ,  108  includes three attachment points  114 ,  116 ,  118  for the articulating links  110 ,  112  disposed along the opposite sides, with only selected ones of the attachment points along the right side (as shown in  FIG. 1 ) of the foldable staircase  100  being labeled with reference numerals in  FIG. 1 , for clarity of illustration. Specifically, each of the treads  102 ,  104 ,  106 ,  108  includes a front tread attachment point  114  disposed adjacent the front edge  120  of the tread  102 ,  104 ,  106 ,  108 , a rear tread attachment point  116  disposed adjacent the rear edge  122  of the tread  102 ,  104 ,  106 ,  108 , and an intermediate tread attachment point  118  disposed substantially halfway between the front and rear tread attachment points  114 ,  116  along each of the opposite edges of the tread  102 ,  104 ,  106 ,  108 .  
         [0050]     The intermediate treads  106 ,  108  are attached to one another by a two pairs of long links  110  having an intermediate long link connection point  124  pivotably attached to the intermediate tread attachment points  118  of the upper and lower intermediate treads  106 ,  108 , and upper and lower long link connection points  126 ,  128  disposed at opposite axial ends of the long links  110 . The upper long link connection points  126  of the long links  110  connected to the intermediate tread attachment points  118  of the upper intermediate tread  106  are pivotably connected to the front tread attachment points  114  of the top tread  102 , and the lower long link connection points  128  of the long links  110  connected to the intermediate tread attachment points  118  of the upper intermediate tread  106  are pivotably connected to the rear tread attachment points  116  of the lower intermediate tread  108 .  
         [0051]     In similar fashion, the upper long link connection points  126  of the long links  110  connected to the intermediate tread attachment points  118  of the lower intermediate tread  108  are pivotably connected to the front tread attachment points  114  of the upper intermediate tread  106 , and the lower long link connection points  128  of the long links  110  connected to the intermediate tread attachment points  118  of the lower intermediate tread  108  are pivotably connected to the rear tread attachment points  114  of the bottom tread  104 .  
         [0052]     The top tread  102  is further pivotably connected to the upper intermediate tread  106  by a pair of short articulating links  112 . Specifically, the short articulating links  112  each include an upper short link connection point  130  pivotably connected to the intermediate tread attachment point  118  of the top tread  102 , and a lower short link  132  connection point pivotably connected to the rear tread attachment point  116  of the upper intermediate tread  106 .  
         [0053]     In similar fashion, the bottom tread  104  is further pivotably connected to the lower intermediate tread  108  by a second pair of the short articulating links  112 . Specifically, the short articulating links  112  attached to the bottom tread  104  each include an upper short link connection point  130  pivotably connected to the front tread attachment point  114  of the lower intermediate tread  108 , and a lower short link  132  connection point pivotably connected to the intermediate tread attachment point  118  of the bottom tread  104 .  
         [0054]     As shown in  FIGS. 12-15 , the short and long articulating links  110 ,  112  are be pivotably attached to the treads  102 ,  104 ,  106 ,  108  by threaded connections including shoulder bolts  134  secured by locking nuts  136 , which provide a controlled clearance fit to facilitate articulation of the links  110 ,  112  with respect to the treads  102 ,  104 ,  106 ,  108 . Washers  138  are provided, inboard of the locking nuts  136  and the head of the shoulder bolts  134 , to spread contact loads into the links  110 ,  112  and the treads  102 ,  104 ,  106 ,  108 .  
         [0055]     The first exemplary embodiment of the foldable staircase  100  includes a pair of latches  140 , as shown in  FIGS. 1-4  and  FIG. 9 , each having an elongated body  142  including a first end  144  pivotably connected to one of the front tread attachment points  114  of the bottom tread  104 , by a threaded connection as shown in  FIG. 14 , including a bolt  134 , a locking nut  136  and a pair of washers  138 . The body  142  of the latches  140  also defines an elongated slot  146 , extending parallel to a longitudinal axis  148  of the latch  140 , for sliding receipt therein, as shown in  FIGS. 9 and 15  of a pivot member, in the form of a clevis pin  150  extending outward from a short link mid-link connection point  152  in the short links  110  attached to the bottom tread  104 . The slot  146  further includes a series of notches  154  therein for engaging the clevis pin  150 , to prevent further pivoting of the treads  102 ,  104 ,  106 ,  108  between the stowed and extended positions, to thereby lock the staircase  100  into rigid structure at a selected one of the extended positions.  
         [0056]     The clevis pin  150  is secured by a cotter pin  156  extending through a cross-drilled hole in the end of the clevis pin  150 . Washers  158  provided inboard of the head of the clevis pin  150  and the cotter pin  156 , to spread contact loads into the links  112  and the latches  140 . By removing the cotter pin  156 , the clevis pin  150  may be selectively disengaged from the short link arm  112  attached to the lower tread  104 , to thereby allow the staircase  100  to be pivoted to the fully extended position for use as a litter or stretcher.  
         [0057]     The short articulating links  112  of the exemplary embodiment have a length between the upper and lower short link connection points  130 ,  132  that is substantially equal to the length between the intermediate long link connection point  124  and both the upper and lower long link connection points  126 ,  128  of the long articulating links  110 . For economy of manufacturing, the short links  110  connecting the top and bottom treads  102 ,  104  to the intermediate treads  106 ,  108  are identical, with all of the short links  112  attached to both the top and bottom treads  102 ,  104  including the mid-link connection point  152  for receiving the clevis pin  150 .  
         [0058]     As will be seen from examining the drawings, the treads  102 ,  104 ,  106 ,  108 , the short and long articulating links  110 ,  112 , and the latches  140  are all configured in the exemplary embodiment to include reinforcing ribs, to provide lightweight but rigid structural members. The treads  102 ,  104 ,  106 ,  108 , the short and long articulating links  110 ,  112 , and the latches  140  may be made from a variety of materials, such as metal, plastic, or composite materials, fabricated by a wide variety of methods. In the first exemplary embodiment of the foldable staircase  100  described above, it is contemplated that the treads  102 ,  104 ,  106 ,  108 , the short and long articulating links  110 , 112  and the latches  140  are preferably formed form a molded plastic or composite material.  
         [0059]     As shown in  FIGS. 10 and 11 , the treads  102 ,  104 ,  106 ,  108  also include a plurality of regularly spaced cup-shaped segments  158  extending downward from the step surface of the treads  102 ,  104 ,  106 ,  108 . These cup-shaped segments  158 , in the exemplary embodiment, are configured generally as right circular cylinders, with open tops and closed bottoms, but with the closed bottoms having a through hole centrally located therein. The through-holes in the cup-shaped segments  158  serve dual functions by letting water flow through the treads  102 ,  104 ,  106 ,  108 , and by allowing attachment of components to the treads  102 ,  104 ,  106 ,  108 . Specifically, as shown in  FIG. 11 , anti skid buttons  160  are attached to the underside of the top step  102 , by means of the through holes in the cup-shaped segments  158 , to provide stability for the upper end of the staircase  100  when it is resting on an elevated surface.  
         [0060]     As further shown in  FIGS. 1, 10  and  11 , the front and rear edges of the treads  102 ,  104 ,  106 ,  108  also include integrally formed hand-holds  162  to facilitate pivoting the treads  102 ,  104 ,  106 ,  108  between the stowed and extended positions.  
         [0061]      FIGS. 6, 7  and  8 A- 8 B, show a second exemplary embodiment of the invention in the form of a foldable staircase  200  having 5 treads, rather than 4 treads, but otherwise identical to the first exemplary embodiment of a foldable staircase  100  described above. Specifically, the second exemplary embodiment of a foldable staircase  200 , according to the invention, includes a top tread  202 , a bottom tread  204 , an upper intermediate tread  206 , a lower intermediate tread  210 , and a middle intermediate tread  209 , operatively connected by on opposite sides (only the right side being shown in the drawings) by pairs of long articulating links  210  and short articulating links  212 , and having a pair of latches  240 , with the construction and operative connection of components of the second exemplary embodiment of a foldable staircase  200  being the same manner as described above in relation to the first exemplary embodiment.  
         [0062]      FIG. 16  shows a first alternate embodiment of a latch apparatus  163 , according to the invention, for locking the treads of a foldable according to the invention, into a desired stowed or extended position. The latch apparatus  163  includes a tie bolt  164  and lever-nut  166 , which replace the shoulder bolts  134  and nuts  136 , etc., along the opposite sides of at least one of the treads, at one of the tread attachment points. By tightening the lever-nut  166 , the articulating links are compressed against the tread at the tread attachment point to lock the treads in a given position. The treads may be pivoted to a different position by loosening the lever-nut  166 .  
         [0063]     Those having skill in the art will recognize that, in practicing the invention, many other types of latches can also be used in combination with the other elements of the invention. For example,  FIG. 17  shows a second alternate embodiment of a latch apparatus  170 , operatively attached between intermediate long-link connection points  172  of two adjacent long-links  174 , operatively connecting two intermediate treads  176 ,  178  of a foldable staircase  180 , in accordance with the invention. The foldable staircase  180  includes a pair of the second alternate embodiments of the latch apparatus  170 , with the latches  170  being attached to opposite sides of the staircase  180 . It will be further noted, that in the embodiment of the foldable staircase  180 , shown in  FIG. 17 , the treads  176 ,  178 ,  182 ,  184 ,  186  are fabricated from aluminum sheet metal, operatively joined by long and short links of a plastic or composite material, similar to those described above in relation to the exemplary embodiment of the foldable pet staircase  100 .  
         [0064]      FIGS. 18 and 19  respectively show enlarged views of a portion of the second alternate embodiment of the latch apparatus  170  in a disengaged and an engaged position, respectively. The latch  170  includes first and second articulating arms  171 ,  173  and a locking knob  175 . The first articulating arm  171  of the latch  170  includes an elongated slot  177  therein, configured for sliding passage therethrough of a threaded fastener (not shown) extending outward from the second articulating arm  173  for threaded engagement with the locking knob  175 . The slot  177  allows the first and second articulating arms  171 ,  173 , of the latch  170 , to be aligned with one another at various extended positions of the staircase  180 , and locked together by tightening the knob  175  to clamp the articulating arms  171 ,  173  securely against one another. The second articulating arm  173  further includes a pair of anti-pivot locking ribs  179 ,  181 , disposed along opposite edges of the second articulating arm  173 , to thereby form a channel  183  configured for receiving the distal end of the first articulating arm  171 , and providing additional support for maintaining the latch  170  in the engaged position shown in  FIG. 19 .  
         [0065]      FIGS. 20 and 22  show a variation of the second embodiment of the latch apparatus  170 , in which the second articulating arm  173  includes an anti-pivot locking rib  181  on only one edge of the second articulating arm  173 .  
         [0066]      FIG. 22  shows a third exemplary embodiment of the invention in the form of a a foldable staircase apparatus  300 , including a foldable staircase  302 , as described above, and a staircase holder  304  adapted for receiving the staircase  302  in the stowed position. The holder  304  includes mounting holes  306  adapted for attaching the holder  304  to a surface, such as the tailgate of a truck or a sport utility vehicle, or a trunk lid of a vehicle.  
         [0067]      FIG. 23  shows a fourth exemplary embodiment of the invention, in the form of a foldable staircase apparatus  400 , including a foldable staircase  402 , as described above, and a mounting bracket  404  for pivotably attaching the staircase  402  to support structure, such as, but not limited to, a vehicle, a watercraft, or a table, so that the staircase  402  may be pivoted about the mounting bracket  404  in the stowed position of the staircase  404 . In other embodiments, the mounting bracket  404  and staircase  402  may be configured so that the staircase  402  may be pivoted about the mounting bracket  404  in only an extended position. In yet other embodiments the mounting bracket  404  and staircase  402  may be configured so that the staircase  402  may be pivoted about the mounting bracket  404  in either the stowed or an extended position. An apparatus  400  including a foldable staircase  402 , as described above, and a mounting bracket  404  may alternatively be configured so that the upper tread of the staircase  402  is releasable attachable to the mounting bracket  404 , before or after extension, to provide stability in use, rather than being permanently pivotably attached.  
         [0068]      FIG. 24  shows a fifth exemplary embodiment  500 , according to the invention, having a foldable staircase  502  pivotably attached by a mounting bracket  504  to a watercraft  506 . As shown in  FIG. 24 , the fifth exemplary embodiment of the invention  500  allows the foldable staircase  502  to be conveniently stowed on the deck  508  of the watercraft  506 , in the manner illustrated in dashed lines in  FIG. 24 , for convenience deployment to aid a pet, such as a dog retrieving water fowl, in disembarking from and re-entering the watercraft  506 . A rotation limiting device, such as the channel shaped bracket  510  shown in  FIG. 24 , a compliant block, or a strut, may be operatively attached to either the watercraft  506 , or the staircase  502 , to provide rotational positioning of the staircase  502  with respect to the watercraft  506 .  
         [0069]      FIG. 25  also illustrates an embodiment  600  of the invention, having a foldable staircase  602  mounted to a ladder  604 , of the type which might extend over the side of a boat or into a swimming pool. The foldable staircase  602  is attached to the ladder  604  by a mounting apparatus  606  having a pair of arms  608  adapted for clamped attachment to rails  610  of the ladder  604 , and a support strut  612  adapted for engaging one of the steps  614  of the ladder  604 .  
         [0070]     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any element not expressly described herein as being essential to the practice of the invention. For example, the use of the term “element” in context with describing certain preferred embodiments of the invention is not intended to limit the invention to structures constructed by welding, or to structures formed from multiple components.  
         [0071]     Preferred embodiments of this invention are described herein, including the best mode known to the inventor for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventor intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited or suggested herein as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.  
         [0072]     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

Summary:
A method and apparatus are provided, for allowing pets to ascend to and descend thereupon, through use of a foldable staircase having a plurality of stair treads operatively connected by articulating links in such a manner that the treads can be pivoted in unison from a stowed position of the staircase, in which the treads are substantially stacked upon one another, to a plurality of extended positions, in which the links position the treads in a spaced and parallel relationship to one another. A latch selectively secures the staircase in a selected one of the extended positions. The latch is configured for preventing further pivoting of the treads in either direction between the stowed and extended positions of the staircase, when the latch is engaged.