referring first to fig1 a and 1b , there is shown in perspective view a first bone cutting assembly 70 of the present invention . this assembly is adapted for use in preparing a contoured cavity in a recipient spinal segment for transplantation of a combination bone / disc allograft harvested from a donor spinal segment . these views show that the first cutting assembly includes a cutting guide ( or jig ) 10 , which has a front side 12 , a rear side 14 , a generally planar bottom side 16 , an arcuate upper side 18 , and cutting slots 20 to guide the exact path of a cutting device , such as a saw blade or cutting burr . in a preferred embodiment of the invention , the cutting slots include an initial short vertical segment 22 which opens to and through the bottom side of the jig . this “ opening slot ” is followed by a longer centrally directed first horizontal segment 24 , followed by an oblique segment 26 directed away from center , and finally a centrally directed second horizontal segment 28 . in this way , a precise dovetail pattern is cut into both the donor and recipient vertebral bodies . two screw holes 30 are disposed on the superior aspect of the top side of the jig for passing screws 32 to secure the jig to the vertebral body during the preparation process . in the central portion 34 of the jig , a cylindrical hole 36 is provided for insertion of an indexing element of a disc measurement stylus , such as a cylindrical indexing peg . the disc measurement stylus 40 of the present invention . the stylus consists of two spaced apart and generally parallel horizontal blades 42 that slide into the annulus fibrosis of the diseased disc on the surface of the bone end plate and establish the depth of bone removal from the vertebral bodies such that the neural elements are protected posteriorly . the blades each include a leading edge 44 , an outer spine 46 , an inner edge 48 , an upper surface 50 , a lower surface 52 , a heel portion 54 , and a bolster 56 . the bolsters are connected with upwardly angling elements 58 of equal length which converge at a vertex to form a central cylindrical peg 60 , which fits within the cylindrical hole 36 of the cutting jig . fig1 b is a lower rear perspective view showing the cutting jig with the attached disc measurement stylus with its blades 42 and its central cylindrical peg 60 placed within the cylindrical indexing hole 36 of the cutting jig 10 . these two elements — the cutting jig and attached disc measurement stylus — comprise the apparatus adapted for performing the first phase of the osteochondral allograft procedure of the present invention , namely , preparation of the transplant site in the recipient patient spinal segment . for simplification these assembled bone and disc cutting elements are variously referred to herein as either the first cutting assembly or “ the recipient bone cutting assembly ” 70 . fig2 a , is a side view in elevation showing a recipient spinal segment rs with the cutting jig 10 and disc measurement stylus 40 of fig1 a - 1b poised for placement on the anterior aspect of the recipient spine . in this instance , the spinal segment is a portion of the lumbar spine . from this position the first of two recipient bone cutting processes will be carried out to define and create the space for placement of a donor osteochondral allograft . the cutting assembly is placed first at the superior vertebral body svbr and the diseased intervertebral disc segment idr . this view also shows the screws 32 positioned for insertion in the screw holes disposed on the superior portion of the top side of the cutting jig . the inferior vertebral body ivbr is not involved in the first cutting process . fig2 b is a side view in elevation showing the first ( recipient ) cutting assembly 70 affixed to the recipient spine rs superior vertebral body svbr with screws 32 threadably inserted into the superior end plate sepr of the vertebral body and the disc measurement stylus 40 with its horizontally disposed blades 42 placed within the annulus fibrosis of the recipient &# 39 ; s diseased disc in such a way as to protect the posterior neural elements . once the cutting jig is secured by screws , the disc measurement stylus may be removed ( see fig2 c ). a cutting device , such as a cutting burr or saw blade 62 , is then inserted into the cutting slots 20 . fig2 c shows how the disc measurement stylus 40 is removed from the annulus fibrosis when the cutting process commences . after passage of the cutting device using the cutting slots of the cutting jig , the screws are unscrewed and the jig is removed from the superior vertebral body . the cut portion of the superior end plate may be removed at this time . preferably , however , this removal may be deferred until completion of the second cutting process of the inferior vertebral body . the residual screw holes shr remain ( see fig3 a - 3b ), as does the new contoured cavity defined within the superior vertebral body that is in continuity with the diseased disc space . fig2 d shows the first cutting assembly 70 inverted from its upright orientation in fig2 a - 2c and positioned for placement on the recipient lower vertebral body immediately under the intervertebral disc . in placing the cutting assembly for the second cutting process , and to effect the proper cavity contour , the edges of the opening slot in the bottom side of the cutting jig are aligned with the corresponding cut edges on the superior vertebral body end plate . fig2 e - 2f show how the cutting process shown in fig2 a - 2c is repeated in a mirror fashion on the inferior vertebral body to complete the second cutting process . again , the cutting assembly is fixed to the inferior vertebral body with screws and the disc measurement stylus with its horizontally disposed blades are placed within the inferior annulus fibrosis of the diseased disc . after passage of the cutting device through the slots of the cutting jig , the screws and the cutting jig are removed . at this point the inferior end plate may be removed , as may the superior end plate , if not already removed . fig3 a - 3b show that when the cut portion bdr is removed after completion of the first and second ( upper and lower ) cutting process , the residual screw holes shr in the inferior vertebral body remain as does the new contoured cavity ccr placed within the superior and inferior vertebral bodies and the intervertebral disc . ( while the various bone tissues are not distinguished in the drawings , it should be understood that the tissue removed from the recipient may include compact bone , cancellous bone , and marrow .) furthermore , the bone bdr can be removed en bloc after the cutting or in a piecemeal fashion using instruments well known to those skilled in the art . in particular in the posterior aspect of the vertebral body , great care is required to avoid inadvertent injury to the dural sac and thus manual preparation of the posterior most segment of ccr is required using instruments such as kerrison rongeurs and pituitary rongeurs . at the end of this segment the ccr should extend all the way from the anterior to the posterior aspect of the vertebral body with the profile contoured to the cutting jig . fig4 and 5 show the second bone cutting assembly employed in the present invention , this assembly including an alignment guide 80 employed for mounting a cutting jig 10 b that matches the earlier described jig to create and harvest a combined bone / disc allograft from a donor which perfectly matches the contoured cavity of the recipient . the donor alignment guide includes an annulus 81 with a plurality of bosses 82 with screw holes 83 for affixing the guide to a donor spinal segment ds ( see fig6 a et seq .) with suitable screws 84 . a central cylindrical indexing peg 85 is disposed slightly above the upper surface 86 of the annulus so that a portion of the bottom side 16 b of the cutting jig can be placed flush with that upper surface 86 . preferably , the indexing peg 85 is supported by either a vertical support or two angled supports 87 , which generally match the supports 58 of the disc measurement stylus . as will be appreciated , the donor alignment guide is sized with an interior diameter 88 sufficiently large to permit placement over a donor spine segment ds after removal of both the spinous processes spd and transverse processes tpd . the assembly comprising the donor alignment guide and the cutting jig may be referred to variously as either “ the harvesting assembly ” or simply the second cutting assembly . as will be appreciated , in both the first and second cutting assemblies , the jig is described as including a hole or receptacle for insertion of an indexing element . however , the transposition of these elements will produce the same indexing function so as to ensure accurate placement of the jig on the stylus or on the alignment guide . accordingly , the disc measurement stylus of the first cutting assembly may include an indexing hole and the jig an indexing peg ; likewise , the donor alignment guide may include an indexing hole corresponding to an indexing peg disposed on the second cutting assembly jig body . fig6 a - 7b illustrate the process of creating and harvesting the combined bone / disc allograft from a donor spine segment using the harvesting assembly . these views show that the donor spine segment is prepared by removing the spine segment from the donor and then removing all or a portion of the spinous processes spd and transverse processes tpd from the superior vertebral body svbd and the inferior vertebral body ivbd , preferably with cuts through the pedicle close to the dorsal aspect of each of the vertebral bodies . the annulus of the donor alignment guide is then placed over the superior vertebral body using fluoroscopic or visual landmarks and is affixed with screws . a cutting device is then inserted through the cutting slots of the jig and employed to make cuts that defines an outer contour of the combined bone / disc allograft that corresponds precisely with the interior edges and walls of the contoured cavity of the recipient . when the first cutting process on the superior vertebral body is completed , the donor alignment guide is removed and inverted for placement on the inferior vertebral body , and the process is then repeated in mirror fashion on the inferior vertebral body . fig7 a - 7b show how the healthy combined bone / disc allograft bda is removed after the cutting processes are completed . the combined bone / disc allograft includes the cut portion of the superior vertebral body svbd ′, the intervening healthy intervertebral allograft disc idd , and the cut portion of the inferior vertebral body ivbd ′. fig8 a shows the prepared portions of the recipient spine segment rs . as noted previously , the residual screw holes shr and the contoured cavity ccr remain . fig8 b shows the recipient spinal segment after implantation of the allograft in the contoured cavities of the superior and inferior vertebral body of the recipient spine . the prepared portion of the superior vertebral body of the graft is placed in the contoured cavity in the recipient &# 39 ; s superior vertebral body ; the prepared portion of the inferior vertebral body of the graft is placed in the contoured cavity in the inferior vertebral body of the recipient ; the healthy allograft intervertebral disc remains attached to the bone of the superior and inferior allograft end plates throughout this process . as will be appreciated , the shape of this exemplary donor allograft and the contoured cavity of the recipient resemble the joining method employed by dovetail tails and pins in woodworking . the principles for cutting , sizing , and fitting the elements are essentially identical . fig9 a - 12b show four different matched pairs of cutting jigs , respectively 9 a - 9 b , 10 a - 10 b , 11 a - 11 b , and 12 a - 12 b . these show that several suitable slot patterns may be employed for preparing the contoured cavity and the allograft , including , without limitation , an angled z pattern , 9 a - 9 b ; a rectangular sled pattern 10 a - 10 b ; an l - shaped pattern 11 a - 11 b ; a rectangular / oval configuration 12 a - 12 b , an oblique / horizontal configuration 13 a - 13 b ; and an oval configuration 14 a - 14 b . as will be appreciated , such patterns may take a virtually unlimited number of practicable shapes , and all be used with both the disc measurement stylus and the allograft donor disc measurement ring to prepare the donor and recipient bone to matching size configurations for maximal contact and stability . as will be appreciated , in each pair of cutting jigs , the donor cutting jigs , 90 in fig9 a , 100 in fig1 a , 110 in fig1 a , 120 in fig1 a , 130 in fig1 a , and 140 in fig1 a , each have slots 92 , 102 , 112 , 122 , 132 , 142 , respectively , with an interior edge 94 , 104 , 114 , 124 , 134 , 144 , respectively , that trace or match the dimensions of the corresponding outer edge 96 , 106 , 116 , 126 , 136 , and 146 , respectively , of the cutting slot 98 , 108 , 118 , 128 , 138 , 148 , of the paired recipient cutting jig 90 ′, 100 ′, 110 ′, 120 ′, 130 ′, 140 ′. in this way , the edges , angles , corners , and overall shape of the allograft is sized to match the prepared contoured cavity in the recipient spine . while in general it is desirable that the slot patterns create both a contoured cavity and a matching allograft that are substantially bilaterally symmetrical along any medial line of symmetry ( i . e ., have reflection symmetry ), other geometries , perhaps less than perfectly regular or symmetrical , are possible . accordingly , the bilaterally symmetrical geometries described and shown herein shall not be considered as limiting . the above disclosure is sufficient to enable one of ordinary skill in the art to practice the invention . the description also provides the best mode of practicing the invention presently contemplated by the inventor . however , while there is provided herein a full and complete disclosure of the preferred embodiments of this invention , the written description and the drawings do not limit the invention to the exact construction , dimensional relationships , and operation shown and described . various modifications , alternative constructions , changes and equivalents will readily occur to those skilled in the art and may be employed , as suitable , without departing from the true spirit and scope of the invention . therefore , the above description and illustrations should not be construed as limiting the scope of the invention , which is defined instead by the appended claims .