Abstract:
A field dressing knife suitable for all aspects of field dressing small and large game is disclosed. Various novel aspects of the knife include: a large butt-end of the handle and a groove near the butt-end of the handle, both to spread the normal stress over a larger surface area when striking the butt-end of the handle with a free hand for splitting pelvis and brisket bones; and a configurable handle, permitting the double-edged field dressing knife to be used in knife mode or in a hatchet mode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   None 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   REFERENCE TO MICROFICHE APPENDIX 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a knife. More specifically, the present invention relates to a field dressing knife for complete field dressing of small and large game and having special application to the severing of the pelvis and brisket bones of small and large game. 
   2. Background Art 
   Soon after a game animal is killed, field dressing is required to inhibit the growth of bacteria, thereby preventing premature spoilage of meat. Field dressing refers to the process of preparing the carcass of a game animal, often at the approximate location the animal was killed, to minimize spoilage and preserve the meat for later consumption. Once all life functions have ceased, the carcass begins to decay. Unchecked bacterial growth of the internal organs (viscera) and body fluids spreads quickly through the carcass causing the meat to be unfit for human consumption in a matter of hours, depending on the ambient temperature. To prevent this, the process of gutting, or evisceration, is performed. Gutting involves removing all viscera inside the abdomen and thorax. Removing viscera prevents bacterial growth in the viscera from spreading to the meat, aids in cooling the meat, and prevents unpleasant visceral body fluids from spreading to the meat. Heat and moisture further increase the spread of bacteria. The process of gutting necessarily includes severing the brisket and pelvis bones of the game animal carcass in order to remove all the viscera contained under these bones and to open these areas up for better air drying and cooling. 
   Several devices have been used over the years by hunters for field dressing large game, especially for severing of the pelvis and brisket bones. One such tool is a handsaw  100  as illustrated in  FIGS. 1 and 2 . Handsaws  100  tend to be large and awkward to carry in the field while hunting. They work better on the brisket, where a full pass of the saw blade is possible, than on the pelvis bone. For splitting the pelvis bone, it is natural to attempt to saw from one end to the other as shown in  FIG. 1 . However, a full pass of the saw blade cannot be made because the area between the pelvis bone and the spine is insufficiently deep. This region also contains both the urethra  110  and colon  120 . Sawing the pelvis with vertical strokes, while the carcass is on its back, results in puncturing these waste tubes and contamination of the meat. 
   Placing the handsaw blade across the exposed pelvis bone, parallel to the spine as shown in  FIG. 2  is more difficult. In this position, the saw teeth engage a minimum of six inches of bone in a large animal such as an elk. Additionally, sawing from the back end of the elk places the tip of the handsaw  100  directly in line with both the colon  120  and the urine bladder  210 . There is, again, danger of meat contamination. 
   Saw blades used for field dressing large game tend to be difficult to clean. As well, bone rapidly dulls the saw  100  which is difficult to sharpen, especially in the field. For complete field dressing of large game, when using a handsaw  100  for severing the pelvis and brisket bones, both the handsaw  100  and a knife must be carried while hunting. 
   Another tool used for splitting the pelvis and brisket bones of large game is a hatchet. A hatchet is heavy for hunters to carry all day. The most convenient way to carry a hatchet is to secure it in a scabbard attached to a belt. The hatchet handle, dangling down below the waist, tends to interfere with tall grass, brush, and trees as the hunter moves through the field or woods. Like the handsaw  100 , a hatchet works better on the brisket bone than on the pelvis bone. Caution must be taken when chopping through the pelvis bone because of the proximity of the urethra  110 , bladder  210 , and colon  120 , as mentioned in conjunction with the handsaw  100 . Unpleasant results due to using a hatchet for splitting the brisket include jagged and sharp bone splinters left protruding from the split brisket. During the removal of the windpipe and lungs, the hunter&#39;s arm, with a knife in hand, must pass through the chopped brisket opening in order to cut tendons. As with the handsaw  100 , two tools—a hatchet and a knife—must be carried while hunting in order to fully field dress game including splitting the pelvis and brisket using the hatchet. 
   Another tool available to hunters for field dressing is a wire saw. Wire saws are compact and light for carrying in the field. However, in use, the end of the wire is difficult to thread under the pelvis bone of a large game carcass to extend out on both ends of the pelvis. A goal is to avoid puncturing the bladder  210  or colon  120 . Once threaded, the wire saw ends can be pulled back and forth to cut the pelvis. One drawback of the wire saw is that it kinks with use and becomes unfit for reuse. The wire saw is typically only used for the pelvis bone since the pelvis bone is sufficiently small for the saw to pass completely under it and pulled from the top. The brisket is typically too large for this. The hunter must then carry a knife, wire saw, and another device for splitting the brisket. 
   Knives with saw blades represent another class of tool used for field dressing. These knives are easy to carry but difficult to use to saw through the pelvis and brisket bones of large game animals. The saw blade included in a knife typically does not have sufficient length to be used horizontally across the pelvis bone. Thus, the saw blade is typically oriented vertically to saw through the pelvis bone from one end to the other, aiming the end of the saw blade toward the spine. Again, the urethra  110  and colon  120  are likely to be punctured and the meat contaminated. Knife saw blades tend to have very pointed teeth that dull rapidly. These teeth are difficult to sharpen. Saw blades included with knives, and particularly those having aggressive saw teeth, are difficult to clean. Bone chips, flesh, and fat lodge in-between the teeth, requiring rubbing and/or brushing for removal. An advantage to the use of a knife saw blade is: only one device needs to be carried while hunting. 
   Present day hunting knives typically have a blade that is too long for the purpose of splitting the pelvis or brisket bones of large game. When impacting such a knife with a stone or stick, as is sometimes done, a misalignment can easily break the knife blade. Additionally, a single-edged blade cannot be effectively worked back and forth in the bone to elongate a groove. As shown in  FIG. 3 , such an attempt will only elongate the groove  310  in the direction of the sharp edge of the blade  300 . 
   A skinning and gutting knife was disclosed by Bloch in U.S. Pat. No. 5,033,987. The longitudinal axis of the handle of this knife is not parallel with the longitudinal axis of the blade. The disclosed method for applying a large impact force is to strike the back of the blade (opposite the edge) with a foreign object encountered in the field, such as a rock or piece of wood. Such application has the potential to damage a knife by applying a force that is not parallel to the plane of the blade. Furthermore, there is no guarantee a foreign object such as a rock or piece of wood will be handy to a hunter, especially in conditions of deep snow. 
   A gutting knife is disclosed in U.S. Pat. No. 6,578,271 by Macek. This knife has two forward extensions with a slot between them. In that slot are saw teeth. A method for severing bone is described as applying the slot to the bone and working the handle up and down to apply the saw teeth to the bone. Because the knife blade extends into the abdominal cavity of the carcass, when applying this knife to the severing of a pelvis bone of a large game animal, the probability of cutting or tearing the urethra  110  or the colon  120  is very high. Bone severed by impact of the knife is not disclosed. 
   There is, therefore a need for a single tool by which small and large game may be field dressed, including the expedient and safe severing of the pelvis and brisket bones. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a single tool by which small and large game may be field dressed, including the severing of the pelvis and brisket bones. An additional object is for a tool that is sufficiently light and compact to be carried by a hunter in the field or woods for extended periods. Further, it is an object of this invention to provide a method for conveniently and efficiently splitting the pelvis and brisket bones of small and large game with the same tool used for other field dressing steps. 
   To effect the above objects, a novel field dressing knife is disclosed. Various embodiments of the field dressing knife include the following design aspects:
         a large surface area at the butt-end of the knife handle,   a circumferential groove near the butt-end of the knife handle for engaging the index finger and thumb of the user, further increasing the effective surface area of the butt-end of the handle,   a double-edged blade, and   a conversion to a hatchet-like device for chopping.       

   The field dressing knife handle butt-end will preferably have a surface area between 1.35 and 10 square inches. 
   In use for splitting the pelvis and brisket bones of large game, the field dressing knife may be held with a gripping hand and the butt-end of the knife handle struck with the user&#39;s free hand to penetrate the cartilage and bone. The great surface area of the butt-end of the field dressing knife, and the additional area provided by the user&#39;s gripping hand, are needed for impacting the butt-end of the knife handle with a hand with sufficient force to sever bone but not so much as to cause a hand injury. 
   After gaining some entrance into the pelvis or brisket bone with the field dressing knife blade, the knife may be worked back and forth to extend the groove made by the knife. Therefore, the blade of the knife is preferably sharp on both edges, so it will cut when worked in both directions. 
   Some hunters have grown accustomed to using a hatchet for splitting the pelvis and brisket bones of their large game. To provide a single tool for both hatchet and knife field dressing operations, the handle of the instant invention may be configured as a knife handle or as a hatchet handle. The handle, when configured for hatchet use, may be angled relative to the blade in a plurality of angles. This feature increases the versatility of the field dressing knife, and permits the user to select the best angle for the instant need. 
   The field dressing knife of the present invention may include a gut hook and a blade suitable for field dressing operations other than splitting bone and severing cartilage. Hence, a single, compact tool may be carried in the field to perform all operations of field dressing. 
   Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a detail view showing a handsaw being used in a vertical orientation for splitting the pelvis bone of a large game carcass; 
       FIG. 2  is a detail view showing a handsaw being used in a horizontal orientation for splitting the pelvis bone of a large game carcass; 
       FIG. 3  is a detail view of a single-edged knife being used for splitting bone; 
       FIG. 4  is a side elevation view of a field dressing knife of the present invention; 
       FIG. 5  is a detail of the field dressing knife showing the handle butt-end groove; 
       FIG. 6  is a plan view showing the field dressing knife being held ready to be struck with a free hand; 
       FIG. 7  is a perspective view of the field dressing knife held in a hand for skinning and cutting; 
       FIG. 8  is a perspective view of the field dressing knife held in position for severing bone by striking with a free hand; 
       FIG. 9  is a side elevation view of a field dressing knife blade, a thumb-push ridge, and finger guard; 
       FIG. 10  is a detail view of a double-edged knife being used for splitting bone; 
       FIG. 11  is a detail of a large animal carcass showing the brisket bone; 
       FIG. 12  is a perspective view of the field dressing knife being used to split the brisket bone of a large animal carcass; 
       FIG. 13  is a side elevation view of a field dressing knife with a handle contracted; 
       FIG. 14  is a side elevation view of a field dressing knife with a handle extended, longitudinal axes of the handle and a blade being parallel; 
       FIG. 15  is a side elevation view of a field dressing knife with a handle extended, longitudinal axes of the handle and a blade being approximately perpendicular; 
       FIG. 16  is a perspective view of a field dressing knife with the handle contracted and held for severing bone; 
       FIG. 17  is a perspective view of a field dressing knife with the handle extended and held for severing bone; 
       FIG. 18  is a perspective view of a field dressing knife with the handle extended and the handle rotated to be used as a hatchet; 
       FIG. 19   a  is a detail view of an additional embodiment of the field dressing knife having a telescopic handle, the handle being in a short mode; 
       FIG. 19   b  is a detail of a latch for the telescopic handle of the additional embodiment; 
       FIG. 19   c  is a cross-sectional shape of the field dressing knife of the additional embodiment; 
       FIG. 20  is a plan view of the additional embodiment of the field dressing knife having a telescopic handle; 
       FIG. 21  is a detail view of an additional embodiment of the field dressing knife having a telescopic handle, the handle being in a long mode; 
       FIG. 22  is an exploded view of a star gear assembly; 
       FIG. 23   a  is a perspective view of a first embodiment of a field dressing knife handle attachment; 
       FIG. 23   b  is a cutaway view of the first embodiment of the field dressing knife handle attachment; 
       FIG. 24   a  is a perspective view of a second embodiment of a field dressing knife handle attachment; 
       FIG. 24   b  is a cutaway view of the second embodiment of the field dressing knife handle attachment; 
       FIG. 25  is a side elevation view of the field dressing knife and separate handle for converting the field dressing knife to a hatchet; 
       FIG. 26  is a side elevation view of the field dressing knife and separate handle configured for use as a hatchet; 
       FIG. 27  is a side elevation view of a folding field dressing knife with the blade out for use; 
       FIG. 28  is a side elevation view of a folding field dressing knife with the blade folded in for storage, transport, and safety; 
       FIG. 29   a  is a side elevation view of the field dressing knife blade with the star gear; 
       FIG. 29   b  is an end view of the field dressing knife blade with the star gear; 
       FIG. 29   c  is a plan view of the field dressing knife blade with the star gear; 
       FIG. 30  is a plan view of the field dressing knife with the handle in its contracted mode; 
       FIG. 31  is a side elevation view of the field dressing knife with the handle in its contracted mode; 
       FIG. 32  is a side elevation view of the field dressing knife with the handle in its extended mode; 
       FIG. 33  is a plan view of the field dressing knife with the handle in its extended mode; 
       FIG. 34  is a first side elevation view of the field dressing knife with the handle in its extended mode and its blade in its hatchet mode; 
       FIG. 35  is a first plan view of the field dressing knife with the handle in its extended mode and its blade in its hatchet mode; 
       FIG. 36  is a second side elevation view of the field dressing knife with the handle in its extended mode and its blade in its hatchet mode; 
       FIG. 37  is a second plan view of the field dressing knife with the handle in its extended mode and its blade in its hatchet mode; 
       FIG. 38  is an exploded view of one embodiment of the extensible field dressing knife handle; 
       FIG. 39  is a perspective view of a broad-headed bolt; and 
       FIG. 40  is an exploded view of an expandable field dressing knife handle. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A longitudinal axis of a handle  410  of a field dressing knife  400  is defined as passing through the handle  410  from the butt end  430  of the handle  410  to the guard end  440  of the handle  410  as shown in  FIG. 4 . The longitudinal axis of the blade  420  is also shown passing from the guard end  440  of the blade to the tip  460  of the blade  420 . These axes are substantially parallel in  FIGS. 4 ,  7 ,  8 ,  13 ,  14 ,  16 ,  17 ,  19   a ,  20 ,  30 - 33 , and  36 . The knife blade  420  will preferably include a gut hook  470 , a blade guard  480 , and a double edge  490 . 
   In one embodiment, near the butt-end  430  of the handle  410 , a groove  510 , detailed in  FIG. 5 , is provided into which to engage a user&#39;s thumb  610  and forefinger  620  as shown in  FIG. 6  for the purpose of severing a pelvis or brisket bone of a small or large animal carcass  1110  (see  FIG. 11 ). A result of the grip arrangement shown in  FIG. 6  is a larger effective surface area on which to strike with a free hand  810  (see  FIG. 8 ) to provide the force to cause the knife blade  420  to enter the bone or cartilage. 
   In  FIG. 7 , a user is shown holding the field dressing knife  400  in a position for cutting, slicing, skinning, etc. 
   Another use, already mentioned, for the field dressing knife  400  is that of bone severing. To effect this process, the field dressing knife  400  is turned to an approximately vertical orientation with the blade tip  460  downward in contact with the bone or cartilage  1010  as illustrated in  FIGS. 8 and 10 . The butt end  430  of the field dressing knife handle  410  is then struck with the user&#39;s free hand  810  to provide the force needed to cause the knife blade tip  460  to enter the bone or cartilage  1010 . Once the knife blade tip  460  has entered the bone or cartilage  1010 , the field dressing knife  400  is worked back and forth according to the arrows  1020  in  FIG. 10 . In this way, the slot caused by the knife blade tip  460  is elongated, furthering the bone or cartilage severing process. 
   An example of a knife blade  420  without the knife handle  410  is shown in  FIG. 9 . In this figure, the blade guard  480  and thumb-push  1320  are shown integral with the knife blade  420 . The present invention is not limited to a guard  480  or a thumb-push  1320  integral with the blade  420 . Note that the blade guard  480  and the thumb-push  1320  may be made integral with the handle  410  instead of the blade  420  as shown in  FIGS. 36 and 37 . 
   A large animal carcass  1110  is shown in  FIGS. 11 and 12 . Preferably, during field dressing, the brisket bone  1120  and the pelvis bone (see  FIGS. 1 and 2 ) should be severed to assist in removing viscera and enhance blood drainage and cooling of the carcass. In  FIG. 12 , the process of severing the brisket bone  1120  is illustrated. The field dressing knife  400  is also shown in operation. 
   A preferred method of splitting the brisket bone  1120  is to drive the field dressing knife  400  off center of the brisket bone  1120  approximately one fourth to one and a half inches. Here, the ribs are softer and connected to the brisket bone  1120  with cartilage, making severing easier. A preferred method of splitting the pelvis bone comprises orienting the knife blade  420  parallel to a center ridge of the carcass pelvis bone and driving the field dressing knife blade tip  460  into the center ridge with the user&#39;s free hand. 
   A novel handle assembly  1310  for the field dressing knife is shown in  FIGS. 13-18 . The handle assembly  1310  may be used in a contracted position as shown in  FIG. 13 , or extended as shown in  FIGS. 14 and 15 . In the extended position, the field dressing knife  400  may be used as a hatchet in which a blade edge  1410  or a tip  460  may be used to strike a bone  1010  for the purpose of severing bone or cartilage  1010 . 
   Another aspect of the embodiment of the field dressing knife  400  shown in  FIGS. 13-15 ,  25 ,  26 ,  29   a ,  31 ,  32 ,  34 ,  36 , and  37  is a thumb-push ridge  1320 . The location and configuration of this thumb-push ridge  1320  is such that a user&#39;s thumb rests against the thumb-push ridge  1320  during some modes of usage, and provides stability, control, and comfort. 
   In the embodiment shown in  FIGS. 13-18 , the handle assembly  1310  may engage the blade  420  in either of two positions. In the position shown in  FIGS. 13-14  and  16 - 17 , the longitudinal axis of the handle  410  is substantially parallel to the longitudinal axis of the blade  420 . In this configuration, the field dressing knife  400  may be used to split bone or cartilage, slice, cut, and skin. In the configuration of  FIG. 14 , the field dressing knife  400  may also be used to chop bone  1010  wherein the edge  1410  is used to strike the bone  1010  and sever bone when gripped as seen in  FIGS. 7 and 14 . 
   When the field dressing knife  400  is configured as shown in  FIGS. 15 ,  18 ,  34 ,  35 , and  37 , it is typically used as a hatchet wherein the knife blade tip  460  strikes the bone or cartilage  1010 . In this configuration, the longitudinal axes of the knife blade  420  and the handle  410  are not substantially parallel, but rather, substantially perpendicular. 
   Preferably, the handle assembly  1310  will extend, giving an overall length of about nine inches for use as a hatchet. The handle assembly  1310  of the present embodiment comprises three sections: the handle  410  and two inner sections  1420  that fit inside the handle  410  section. The inner sections  1420  includes threads  1430  for engaging a knife blade block  1440 , being defined for the purposes of this document as the portion between the blade guard  480  and the handle, and is integral with the knife blade  420 . The knife blade block  1440  includes two apertures with female threads into which the threads  1430  of the inner sections  1420  are alternately engaged. 
     FIGS. 16-18  show the field dressing knife  400  in various modes of use. The versatility of the field dressing knife  400  is evident in these figures. Extending the handle assembly  1310  for striking the butt end  430  of the handle  410  with the user&#39;s free hand  810  may provide a better working position or angle for accomplishing the requisite bone or cartilage severing process. 
   An additional embodiment of the field dressing knife  400  is shown in  FIGS. 19   a - 21 . In this embodiment, the included angle, θ 2110 , between the longitudinal axis of the blade  420  and the longitudinal axis of the handle  410  is varied by mating two halves of a star gear  1910  in various configurations. The included angle, θ 2110 , may take on values from approximately 45 degrees to 315 degrees. 
   A star gear  1910  is defined herein as a construct as detailed in  FIG. 22  having two symmetrical, mating halves  2210 ,  2220 . Because of their symmetry, said mating halves  2210 ,  2220  may be engaged one to another in a plurality of configurations all having a common axis. In order to change the mating configuration, the two halves  2210 ,  2220  are rotated relative to one another on the common axis of rotation  2230 . The shape needs only be symmetric, a multi-pointed star shape is not necessary to this definition. The above definition is used herein, including in the claims. 
   The two symmetric, mating halves  2210 ,  2220  of the star gear  1910  are held together with a special, T-headed bolt  2240  while the field dressing knife  400  is in use. In the preferred embodiment, the T-headed bolt  2240  is held engaged in the female half  2210  of the star gear  1910  by engaging a snap ring  2250  to a groove  2280  in the T-headed bolt  2240  after inserting the T-headed bolt  2240  through an aperture  2260  in the female half  2210  of the star gear  1910 . Said snap ring  2250  has an outer diameter or dimension greater than that of the aperture  2260 . 
   The threaded end of the T-headed bolt  2240  is threaded into female threads in an aperture  2270  of the male half  2220  of the star gear  1910 . Unthreading the T-headed bolt  2240  draws the female half  2210  of the star gear  1910  away from the male half  2220  because the snap ring  2250  engages an inside surface of the female half  2210  around the aperture  2260 . When the T-headed bolt  2240  is tightened down, the mating halves  2210 ,  2220  of the star gear  1910  are held firmly together so that the field dressing knife  400  may be used for slicing, chopping, piercing, etc. without fear that the included angle, θ 2110 , of the longitudinal axis of the blade  420  to that of the handle  410  will change under force. 
   Details of the handle  410  assembly are also shown in  FIGS. 19   a - 21 . The handle of this embodiment comprises two sections  1920 ,  1930 . At least one inner section  1930  fits slidably inside the outer section  1920  so that the two sections  1920 ,  1930  may telescope to produce a longer and a shorter handle  410 . The cross sectional shape of the sections  1920 ,  1930  is preferably non-circular such as the oval or ellipse shown in  FIG. 19   c . Other non-circular shapes are viable such as polygons. Because of the non-circular cross section, the sections  1920 ,  1930  do not rotate relative to one another. 
   The two sections  1920 ,  1930  are held in the shorter arrangement shown in  FIGS. 19   a  and  20 , and secured in the longer arrangement shown in  FIG. 21  by a spring lock assembly  1940 . The spring lock assembly  1940  comprises a button  1950  (see also  FIG. 19   b ) which engages an aperture in the inner handle section  1930  and engages the outer handle section  1920  in two ways to cause the two sections  1920 ,  1930  to maintain a given configuration with respect to one another. When the handle  410  is in its short mode, the button  1950  engages an aperture toward the butt-end of the outer section  1920 . When the handle  410  is in its long mode, the button  1950  engages an edge of the outer section  1920  nearest the blade as shown in  FIG. 21 . In the long mode, the handle sections  1920 ,  1930  are held strongly in their respective positions by the matching tapered regions  2120 ,  2130  engaged to one another. The button  1950 , in this case, represents added security. 
   The button  1950  is forced outward by a spring  1960 . The spring  1960  may be a coil spring or an elastic material such as rubber. 
   A Z-clip  1970  is made to engage a notch  1980  in the button  1950  when the button  1950  is sufficiently depressed. The thickness of the outer section  1920  wall is sufficiently great in the vicinity of the butt-end aperture to disallow the button  1950  from being adequately depressed to engage the Z-clip  1970 . In use, the button  1950  is depressed when the field dressing knife handle  410  is in its short mode as shown in  FIGS. 19   a  and  20  in order to extend the handle  410  to its long mode as shown in  FIG. 21 . In this instance, the Z-clip  1970  does not engage in the button notch  1980 , but as the outer handle section  1920  is pulled away from the blade  420 , the button  1950  slips under the outer section  1920  housing and is thereby disallowed from being forced further outward by the spring  1960 . The outer section  1920  of the handle  410  is slid further away from the knife blade  420  until the button  1950  is able to slide through the aperture in the inner section  1930  past the edge of the outer section  1920  closest to the blade  420 . At this point, the spring  1960  forces the button  1950  outward to secure the two handle sections  1920 ,  1930  stationary with respect to one another. 
   To return the handle  410  to its short mode, the button  1950  is again depressed by the operator, this time until the Z-clip engages the notch  1980  in the button  1950 . The button  1950  is thereby held in its depressed state while the user uses both hands to return the outer section  1920  of the handle  410  back toward the field dressing knife blade  420  to the short mode. A finger  1990  engages the butt-end of the outer section  1920  when the outer section  1920  has been adequately forced toward the blade  420 . The finger  1990  in turn engages an appendage  1995  ( FIG. 19   b ) of the Z-clip  1970 , forcing the Z-clip  1970  to disengage from the button notch  1980  and permitting the button  1950  to engage into the aperture of the outer section  1920  nearest the butt-end of the handle  410 . 
   The mating tapered regions  2120 ,  2130  in the handle sections  1920 ,  1930  are machined or formed accurately to provide firm, rigid engagement of the two sections  1920 ,  1930  when the handle  410  is in the long mode. The handle  410  is transformed from the short mode to the long mode by depressing the button  1950  while holding the outer section  1920  in a vertical position with the blade  420  downward. When the button is depressed, the handle  410  is raised as the handle  410  extends due to gravity and snaps into place. Due to a small amount of elasticity and the friction between the two handle sections  1920 ,  1930 , the two handle sections  1920 ,  1930  wedge tightly and rigidly. At this point, the button  1950  returns to its outward position under the force of the spring  1960 , to help secure the two handle sections  1920 ,  1930  in their positions relative to one another. 
   Due to the firm engagement of the two handle sections  1920 ,  1930 , a relatively large, sharp force must be applied to return the handle  410  to its short mode. Therefore, the button  1950  is made to lock down with the engagement of the Z-clip  1970  in the button notch  1980  when the button  1950  is sufficiently depressed. When the button  1950  is in its locked-down position, the user is free to use both hands to apply the large force required to free the tapered regions  2120 ,  2130  in the two handle sections  1920 ,  1930  from one another. To apply an adequate force, the blade  420  of the field dressing knife  400  is placed in a sheath or scabbard (not shown). The sheath is firmly gripped and the knife  400  swung by the user&#39;s arm with the handle butt-end  430  downward to strike a safe object such as the ground. With the button  1950  depressed, the outer section  1920  is free to return over the inner section  1930 . In this process, it is very helpful that the button  1950  not require continual depressing. 
   An optional aspect of the present invention is shown in  FIGS. 19   a  and  21 . Gage lines  2140  are shown to provide guidance to the user regarding the depth in which the blade  420  has been driven into bone or cartilage in the process of splitting the pelvic bone or the brisket bone of a small or large animal carcass. The gage lines  2140  may be forged, machined, or etched into the blade  420 . Any other suitable approach, providing permanent, robust gage lines  2140  may be used. The present invention is not limited to a specific process of providing these gage lines  2140 . 
   An additional advantage of the present embodiment over the prior art, as shown in  FIG. 4 , is the tapering or monotonic increase of the cross sectional area of the field dressing knife handle  410  from the blade  420  to the butt-end. This construction greatly enhances a user&#39;s ability to grip the knife  400  when the knife  400  is in use. 
   Three additional embodiments of the field dressing knife  400  are shown in  FIGS. 23   a ,  23   b ,  24   a , and  24   b . In these embodiments, an existing knife may be enhanced by the addition of a broadened end cap  2310 ,  2410 . In the first embodiment shown in FIGS.  23   a  and  23   b , an insert  2320  of the broadened end cap  2310  is inserted into a socket in the end of the knife. The broadened end cap has a butt-end  430  having a large surface area, and a groove  510  for receiving a user&#39;s index finger and thumb, both as discussed for the other embodiments of the field dressing knife  400 . 
   In the second embodiment, also shown in  FIGS. 23   a  and  23   b , the broadened end cap  2310  is made of an elastic material and the narrow section  2320  is stretched over the butt end of the handle of an existing knife. The broadened end cap  2310  is held tightly by the elasticity. 
   The third embodiment of the broadened end cap  2410  is shown in  FIGS. 24   a  and  24   b . In this embodiment, the broadened end cap  2410  slides over the existing handle of the knife, and is held tight by snugly wrapping a strap  2420  about a base of the broadened end cap  2410 . The strap is fitted with hook and loop fasteners. A slot  2430  provides sufficient flexure so the broadened end cap  2410  may be tightened down over the knife handle. The broadened end cap  2410  has a mushroom shape, providing a gripping place  2440  for the user&#39;s index finger and thumb as before. 
   Another valid securing method for the broadened end cap  2310  is threading. Male threads provided on the insert  2320  with corresponding female threads in the handle, or female threads on the first embodiment broadened end cap  2410  with corresponding male threads on the knife handle would be provided. The use of the broadened end caps  2310 ,  2410  would provide to an existing knife some of the advantages described herein for the field dressing knife  400 . 
   It should be noted a separate hatchet handle  2510  for configuring the field dressing knife  400  may be used as clearly shown in  FIGS. 25 and 26 . In this case, the hatchet handle  2510  is carried by the hunter, in addition to the field dressing knife  400 . The hatchet handle  2510  may be extensible, or of fixed length and may be attached at included angles less than or greater than 90 degrees. The field dressing knife  400  and hatchet handle  2510  may attach in a variety of ways, including the threads  2520 , shown, wedging, pinning, clipping, etc. The present invention is not limited to a particular attachment method. 
   An additional embodiment of the field dressing knife  400  is illustrated in  FIGS. 27 and 28 . In this embodiment, the blade  420  of the field dressing knife  400  is foldable into the handle  410  for safety, transport, convenience, portability, etc. A spring clip  2710  provides the security to hold the knife blade  420  in place, both in use and in the folded position as shown in  FIG. 28 . To release the blade  420 , the spring clip  2710  is pressed with a user&#39;s digit at a depression  2720  in the handle against the force of a spring  2730 . The spring clip  2710  rotates about a pivot  2740  which lifts the blade-end of the spring clip  2710  to release the blade  420 . 
   The handle of the folding field dressing knife  400  has the same broadened butt-end  430  and groove  510  as discussed above. 
     FIGS. 29   a - c  show the field dressing knife blade  420  with the star gear  1910 , both separated from the remainder of the field dressing knife. 
   Still another embodiment of the extending field dressing knife is shown in  FIGS. 30-38 . A bolt  3010  with a broad head  3020  and a special circumferential groove  3910  on the shank  3040  side of the broad head  3020  is shown in  FIG. 39 . The diameter of the shank  3040  of the bolt  3010  is no larger than the minor diameter of the threaded region  3920  for a reason that will become apparent following. 
   The bolt  3010  is inserted into the handle  410  as shown in  FIGS. 30-32  so the broad head  3020  of the bolt  3010  makes up the butt-end  430  of the handle  410 . The male threaded region  3920  of the bolt  3010  engages either of two female threaded regions  3810 ,  3820  within the inner section  3030  of the handle depending on whether the handle is in its extended mode ( FIGS. 32-37 ) or its contracted mode ( FIGS. 30-31 ). The bolt  3010  is retained in the field dressing knife handle  410  by, preferably, three or four retaining screws  3050  engaging the special circumferential groove  3910  but generally fitting loosely in the groove  3910  so the bolt  3010  is free to turn. The retaining screws  3050  are preferably threaded into the outer section  3840  of the field dressing knife handle  410 . 
   When the handle  410  is in its contracted position, as shown in  FIGS. 30-31 , the male threads  3920  of the bolt  3010  are engaged in the female threads  3810  of the inner handle section  3830  closest to the knife blade  420 . The groove  3910  of the broad bolt head  3020  firmly engages the retaining screws  3050  to hold the two knife handle sections  3830 ,  3840  together. 
   To extend the field dressing knife handle  410 , the broad-headed bolt  3010  is turned by its broad head  3020  by the user to disengage the bolt threads  3920  from the handle threads  3810  closest to the knife blade  420 . The outer section  3840  of the knife handle  410  is pulled in a direction away from the knife blade  420  until the bolt threads  3920  can engage the handle threads  3820  nearest the butt-end of the knife handle  410 . Therefore, the shank  3040  of the broad-headed bolt  3010  must be able to slide through the handle threads  3820  nearest the butt-end of the knife handle  410 . Thus, the shank  3040  must have a diameter no greater than the minor diameter of its threads. The bolt  3010  is turned again in the same direction as before to fully engage the handle threads  3820  nearest the butt-end of the knife handle  410  as shown in  FIGS. 32-37 . Again, with the retaining screws  3050  engaged in the groove  3910  of the broad bolt head  3020  and the bolt threads  3920  from the handle threads  3820  nearest the butt-end of the knife handle  410 , the two knife handle sections  3830 ,  3840  are rigidly positioned relative to one another. 
   The cross-sectional shape of the two knife handle sections  3830 ,  3840  is preferably round, however, the present invention is not limited thereto. 
   Comparing  FIGS. 32 and 36 , it can be seen that the thumb-push  1320  and finger guard  3510  may be part of the knife blade  420  or the knife handle  410 . 
   In all of  FIGS. 30-38 , the cross section of the field dressing knife handle  410  is preferably circular. 
   A structure for securing the two sections  3830 ,  3840  is clarified in  FIG. 40 . Again, tapers  4010 ,  4020  are mated and the slight elasticity and friction between the inner handle section  3830  and the outer handle section  3840  provides a very rigid coupling of the two sections  3830 ,  3840 . The broad-headed bolt  3010  is used to both disengage the tapers  4010 ,  4020  and also engage the tapers  4010 ,  4020  by the force the bolt applies via its threads  3920 . 
   The above embodiments are the preferred embodiments, but this invention is not limited thereto. It is, therefore, apparent that many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 
   In the following claims, the word “bone” is herein defined as either bone or cartilage.