Exhibit 10.3

                                     FORM OF

                          REGISTRATION RIGHTS AGREEMENT

            Registration Rights Agreement (this "Agreement"), made and entered
into as of May 24, 2006, by and among Osteologix, Inc., a Georgia corporation
(the "Company"), Castle & Morgan Holdings, Inc. ("MergerCo") and the purchasers
signatory hereto (each such purchaser, a "Purchaser" and collectively, the
"Purchasers").

            This Agreement is made pursuant to and in connection with (i) the
Subscription Agreements between the Company and each Purchaser dated as of the
date hereof (collectively, the "Purchase Agreements"), (ii) the Private
Placement Memorandum dated April 28, 2006 relating to the offering of securities
of the Company pursuant to which the Purchasers purchased the Registrable
Securities (the "Memorandum") and (iii) the proposed merger (the "Merger") of
MergerCo with the Company by share exchange.

            The Company MergerCo and the Purchasers hereby agree as follows:

      1. Definitions. Capitalized terms used and not otherwise defined herein
that are defined in the Purchase Agreement shall have the meanings given such
terms in the Purchase Agreement. As used in this Agreement, the following terms
shall have the following meanings:

            "Advice" shall have the meaning set forth in Section 6(d).

            "Business Day" means any day except Saturday, Sunday and any day
      which shall be a federal legal holiday or a day on which banking
      institutions in the State of New York are authorized or required by law or
      other governmental action to close.

            "Commission" shall mean the Securities and Exchange Commission.

            "Common Stock" shall mean shares of Common Stock of MergerCo.

            "Effectiveness Date" means, with respect to the Registration
      Statement required to be filed hereunder, the earlier of (a) the 150th
      calendar day following the effective date of the Merger, or 180 days
      following the effective date of the Merger if the Registration Statement
      is subject to review and comment from the Commission, provided that if
      such day is not a Business Day, then the next Business Day thereafter, and
      (b) the fifth Trading Day following the date on which the Company is
      notified by the Commission that the Registration Statement will not be
      reviewed or is no longer subject to further review and comments.

            "Effectiveness Period" shall have the meaning set forth in Section
      2(a).

            "Event" shall have the meaning set forth in Section 2(b).

            "Event Date" shall have the meaning set forth in Section 2(b).

            "Exchange Act" means the Securities Exchange Act of 1934, as
      amended.

            "Filing Date" means, with respect to the Registration Statement
      required to be filed hereunder, the 45th calendar day following the
      effective date of the Merger, provided that if such day is not a Business
      Day, then the Filing Date shall be the next Business Day thereafter.
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            "Holder" or "Holders" means the holder or holders, as the case may
      be, from time to time of Registrable Securities.

            "Indemnified Party" shall have the meaning set forth in Section
      5(c).

            "Indemnifying Party" shall have the meaning set forth in Section
      5(c).

            "Losses" shall have the meaning set forth in Section 5(a).

            "Plan of Distribution" shall have the meaning set forth in Section
      2(a).

            "Proceeding" means an action, claim, suit, investigation or
      proceeding (including, without limitation, an investigation or partial
      proceeding, such as a deposition), whether commenced or threatened.

            "Prospectus" means the prospectus included in the Registration
      Statement (including, without limitation, a prospectus that includes any
      information previously omitted from a prospectus filed as part of an
      effective registration statement in reliance upon Rule 430A promulgated
      under the Securities Act), as amended or supplemented by any prospectus
      supplement, with respect to the terms of the offering of any portion of
      the Registrable Securities covered by the Registration Statement, and all
      other amendments and supplements to the Prospectus, including
      post-effective amendments, and all material incorporated by reference or
      deemed to be incorporated by reference in such Prospectus.

            "Registrable Securities" means (i) the Shares, and (ii) together
      with any shares of Common Stock issued or issuable upon any stock split,
      dividend or other distribution, recapitalization or similar event with
      respect to the foregoing.

            "Registration Statement" means the registration statements required
      to be filed by MergerCo hereunder, including (in each case) the
      Prospectus, amendments and supplements to the registration statement or
      Prospectus, including pre- and post-effective amendments, all exhibits
      thereto, and all material incorporated by reference or deemed to be
      incorporated by reference in the registration statement.

            "Rule 415" means Rule 415 promulgated by the Commission pursuant to
      the Securities Act, as such Rule may be amended from time to time, or any
      similar rule or regulation hereafter adopted by the Commission having
      substantially the same purpose and effect as such Rule.

            "Rule 424" means Rule 424 promulgated by the Commission pursuant to
      the Securities Act, as such Rule may be amended from time to time, or any
      similar rule or regulation hereafter adopted by the Commission having
      substantially the same purpose and effect as such Rule.

            "Shares" means the shares of Common Stock issued or issuable to each
      Purchaser pursuant to the Merger.

            "Securities Act" means the Securities Act of 1933, as amended.

            "Trading Day" means (i) a day on which the Common Stock is traded on
      a Trading Market, or (ii) if the Common Stock is not listed on a Trading
      Market, a day on which the Common Stock is traded on the over-the-counter
      market, as reported by the OTC Bulletin Board, or (iii) if the Common
      Stock is not quoted on the OTC Bulletin Board, a day on which the Common
      Stock is quoted in the over-the-counter market as reported by Pink Sheets
      LLC (or any similar organization or agency succeeding to its functions of
      reporting prices); provided, that in the event that the Common Stock is
      not listed or quoted as set forth in (i), (ii) and (iii) hereof, then
      Trading Day shall mean a Business Day.


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<PAGE>

            "Trading Market" means the following markets or exchanges on which
      the Common Stock is listed or quoted for trading on the date in question:
      the American Stock Exchange, the New York Stock Exchange, the Nasdaq
      National Market, the Nasdaq SmallCap Market or the OTC Bulletin Board.

            "Transaction Documents" means this Agreement and the Purchase
      Agreement and any other documents or agreements executed in connection
      with the transactions contemplated hereunder and thereunder.

      2. Registration.

            (a) On or prior to the Filing Date, MergerCo shall prepare and file
      with the Commission the Registration Statement covering the resale of all
      of the Registrable Securities for an offering to be made on a continuous
      basis pursuant to Rule 415. The Registration Statement required hereunder
      shall be on Form SB-2 (or another appropriate form in accordance
      herewith). The Registration Statement required hereunder shall contain
      (except if otherwise directed by the Holders) substantially the "Plan of
      Distribution" attached hereto as Annex A. Subject to the terms of this
      Agreement, MergerCo shall use its best efforts to cause the Registration
      Statement to be declared effective under the Securities Act as promptly as
      possible after the filing thereof, but in any event not later than the
      Effectiveness Date, and shall use its best efforts to keep the
      Registration Statement continuously effective under the Securities Act
      until the date when all Registrable Securities covered by the Registration
      Statement have been sold or may be sold without volume restrictions
      pursuant to Rule 144(k) (the "Effectiveness Period").

            (b) If: (i) a Registration Statement is not filed on or prior to the
      Filing Date (if the Registration Statement is filed without affording the
      Holder the opportunity to review and comment on the same as required by
      Section 3(a), MergerCo shall not be deemed to have satisfied such filing
      requirement), or (ii) MergerCo to file with the Commission a request for
      acceleration in accordance with Rule 461 promulgated under the Securities
      Act, within five Trading Days of the date of notification (orally or in
      writing, whichever is earlier) by the Commission that a Registration
      Statement will not be "reviewed," or is not subject to further review, or
      (iii) prior to the date when such Registration Statement is first declared
      effective by the Commission, the Company fails to cause MergerCo to file a
      pre-effective amendment and otherwise respond in writing to comments made
      by the Commission in respect of such Registration Statement within 21
      calendar days after the receipt of comments by or notice from the
      Commission that such amendment is required in order for a Registration
      Statement to be declared effective (or within ten calendar days after
      MergerCo's accountants furnish the requisite financial statements, if
      later), or (iv) a Registration Statement filed or required to be filed
      hereunder is not declared effective by the Commission on or before the
      Effectiveness Date, or (v) after a Registration Statement is first
      declared effective by the Commission, it ceases for any reason to remain
      continuously effective as to all Registrable Securities for which it is
      required to be effective, or the Holders are not permitted to utilize the
      Prospectus therein to resell such Registrable Securities, for in any such
      case 15 calendar consecutive days but no more than an aggregate of 30
      Trading Days during any 12 month period (which need not be consecutive
      Trading Days)(any such failure or breach being referred to as an "Event,"
      and for purposes of clause (i) or (iv) the date on which such Event
      occurs, or for purposes of clause (ii) the date on which such five Trading
      Day period is exceeded, or for purposes of clause (iii) the date which
      such 21 calendar days is exceeded, or for purposes of clause (v) the date
      on which such 30 calendar day or 15 Trading Day period, as applicable, is
      exceeded being referred to as "Event Date"), then in addition to any other
      rights the Holders may have hereunder or under applicable law: (x) on each
      such Event Date the Company shall pay to each Holder an amount in cash, as
      partial liquidated damages and not as a penalty, equal to 2.0% of the
      aggregate purchase price paid by such Holder pursuant to the Purchase
      Agreement for any Registrable Securities then held by such Holder; and (y)
      on each monthly anniversary of each such Event Date (if the applicable
      Event shall not have been cured by such date) until the applicable Event
      is cured, MergerCo shall pay to each Holder an amount in cash, as partial
      liquidated damages and not as a penalty, 2.0% of the aggregate purchase
      price paid by such Holder pursuant to the Purchase Agreement for any
      Registrable Securities then held by such Holder. If MergerCo fails to pay
      any partial liquidated damages pursuant to this Section in full within
      seven days after the date payable, MergerCo will pay interest thereon at a
      rate of 18% per annum (or such lesser maximum amount that is permitted to
      be paid by applicable law) to the Holder, accruing daily from the date
      such partial liquidated damages are due until such amounts, plus all such
      interest thereon, are paid in full. The partial liquidated damages
      pursuant to the terms hereof shall apply on a daily pro-rata basis for any
      portion of a month prior to the cure of an Event.


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<PAGE>

      3. Registration Procedures.

            In connection with the registration obligations in Section 2 hereof,
      MergerCo shall:

            (a) Not less than five Trading Days prior to the filing of the
      Registration Statement or any related Prospectus or any amendment or
      supplement thereto (i) furnish to the Holders copies of all such documents
      proposed to be filed (including documents incorporated or deemed
      incorporated by reference to the extent requested by such Person) which
      documents will be subject to the review of such Holders and (ii) cause its
      officers, directors, counsel and independent certified public accountants
      to respond to such inquiries as shall be necessary, in the reasonable
      opinion of respective counsel, to conduct a reasonable investigation
      within the meaning of the Securities Act. MergerCo shall not file the
      Registration Statement or any such Prospectus or any amendments or
      supplements thereto to which the Holders of a majority of the Registrable
      Securities shall reasonably object in good faith, provided that the
      Company or MergerCo is notified of such objection in writing no later than
      three Trading Days after the Holders have been so furnished copies of such
      documents.

            (b) (i) Prepare and file with the Commission such amendments,
      including post-effective amendments, to the Registration Statement and the
      Prospectus used in connection therewith as may be necessary to keep the
      Registration Statement continuously effective as to the applicable
      Registrable Securities for the Effectiveness Period and prepare and file
      with the Commission such additional Registration Statements in order to
      register for resale under the Securities Act all of the Registrable
      Securities; (ii) cause the related Prospectus to be amended or
      supplemented by any required Prospectus supplement and, as so supplemented
      or amended, to be filed pursuant to Rule 424; (iii) respond as promptly as
      reasonably possible to any comments received from the Commission with
      respect to the Registration Statement or any amendment thereto and, as
      promptly as reasonably possible, upon request, provide the Holders true
      and complete copies of all correspondence from and to the Commission
      relating to the Registration Statement; and (iv) comply in all material
      respects with the provisions of the Securities Act and the Exchange Act
      with respect to the disposition of all Registrable Securities covered by
      the Registration Statement during the applicable period in accordance with
      the intended methods of disposition by the Holders thereof set forth in
      the Registration Statement as so amended or in such Prospectus as so
      supplemented.


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<PAGE>

            (c) Notify the Holders of Registrable Securities as promptly as
      reasonably possible and confirm such notice in writing promptly following
      the day (i)(A) when a Prospectus or any Prospectus supplement or
      post-effective amendment to the Registration Statement is proposed to be
      filed; (B) when the Commission notifies MergerCo whether there will be a
      "review" of the Registration Statement and whenever the Commission
      comments in writing on the Registration Statement (the Company shall cause
      MergerCo, upon request, to provide true and complete copies thereof and
      all written responses thereto to each of the Holders); and (C) with
      respect to the Registration Statement or any post-effective amendment,
      when the same has become effective; (ii) of any request by the Commission
      or any other Federal or state governmental authority during the period of
      effectiveness of the Registration Statement for amendments or supplements
      to the Registration Statement or Prospectus or for additional information;
      (iii) of the issuance by the Commission or any other federal or state
      governmental authority of any stop order suspending the effectiveness of
      the Registration Statement covering any or all of the Registrable
      Securities or the initiation of any Proceedings for that purpose; (iv) of
      the receipt by MergerCo of any notification with respect to the suspension
      of the qualification or exemption from qualification of any of the
      Registrable Securities for sale in any jurisdiction, or the initiation or
      threatening of any Proceeding for such purpose; and (v) of the occurrence
      of any event or passage of time that makes the financial statements
      included in the Registration Statement ineligible for inclusion therein or
      any statement made in the Registration Statement or Prospectus or any
      document incorporated or deemed to be incorporated therein by reference
      untrue in any material respect or that requires any revisions to the
      Registration Statement, Prospectus or other documents so that, in the case
      of the Registration Statement or the Prospectus, as the case may be, it
      will not contain any untrue statement of a material fact or omit to state
      any material fact required to be stated therein or necessary to make the
      statements therein, in light of the circumstances under which they were
      made, not misleading; (vi) the occurrence or existence of any pending
      corporate development with respect to MergerCo that the Company or
      MergerCo believes may be material and that, in the determination of the
      Company or MergerCo, makes it not in the best interest of MergerCo to
      allow continued availability of the Registration Statement or Prospectus;
      provided that any and all of such information shall remain confidential to
      each Holder until such information otherwise becomes public, unless
      disclosure by a Holder is required by law; provided, further,
      notwithstanding each Holder's agreement to keep such information
      confidential, the Holders make no acknowledgement that any such
      information is material, non-public information.

            (d) Use commercially reasonable efforts to avoid the issuance of,
      or, if issued, obtain the withdrawal of (i) any order suspending the
      effectiveness of the Registration Statement or (ii) any suspension of the
      qualification (or exemption from qualification) of any of the Registrable
      Securities for sale in any jurisdiction, at the earliest practicable
      moment.

            (e) Furnish to each Holder, without charge, at least one conformed
      copy of the Registration Statement and each amendment thereto, including
      financial statements and schedules, all documents incorporated or deemed
      to be incorporated therein by reference to the extent requested by such
      Holder, and all exhibits to the extent requested by such Holder (including
      those previously furnished or incorporated by reference) promptly after
      the filing of such documents with the Commission.

            (f) Promptly deliver to each Holder, without charge, as many copies
      of the Prospectus or Prospectuses (including each form of prospectus) and
      each amendment or supplement thereto as such Holder may reasonably request
      in connection their resales. Subject to the terms of this Agreement, the
      Company and MergerCo hereby consent to the use of such Prospectus and each
      amendment or supplement thereto by each of the selling Holders in
      connection with the offering and sale of the Registrable Securities
      covered by such Prospectus and any amendment or supplement thereto, except
      after the giving on any notice pursuant to Section 3(c).


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<PAGE>

            (g) Prior to any resale of Registrable Securities by a Holder, use
      its commercially reasonable efforts to register or qualify or cooperate
      with the selling Holders in connection with the registration or
      qualification (or exemption from such registration or qualification) of
      such Registrable Securities for the resale by the Holder under the
      securities or Blue Sky laws of such jurisdictions within the United States
      as any Holder reasonably requests in writing, to keep each such
      registration or qualification (or exemption therefrom) effective during
      the Effectiveness Period and to do any and all other acts or things
      reasonably necessary to enable the disposition in such jurisdictions of
      the Registrable Securities covered by the Registration Statement;
      provided, that neither Company nor MergerCo shall be required to qualify
      generally to do business in any jurisdiction where it is not then so
      qualified if qualification would subject the Company or MergerCo to any
      material tax in any such jurisdiction where it is not then qualified or
      subject it to file a general consent to service of process in any such
      jurisdiction.

            (h) If requested by the Holders, cooperate with the Holders to
      facilitate the timely preparation and delivery of certificates
      representing Registrable Securities to be delivered to a transferee
      pursuant to the Registration Statement, which certificates shall be free,
      to the extent permitted by the Purchase Agreement and applicable law, of
      all restrictive legends, and to enable such Registrable Securities to be
      in such denominations and registered in such names as any such Holders may
      request.

            (i) Upon the occurrence of any event contemplated by Section
      3(c)(v), as promptly as reasonably possible, prepare a supplement or
      amendment, including a post-effective amendment, to the Registration
      Statement or a supplement to the related Prospectus or any document
      incorporated or deemed to be incorporated therein by reference, and file
      any other required document so that, as thereafter delivered, neither the
      Registration Statement nor such Prospectus will contain an untrue
      statement of a material fact or omit to state a material fact required to
      be stated therein or necessary to make the statements therein, in light of
      the circumstances under which they were made, not misleading. If the
      Company or MergerCo notifies the Holders in accordance with clauses (ii)
      through (v) of Section 3(c) above to suspend the use of any Prospectus
      until the requisite changes to such Prospectus have been made, then the
      Holders shall suspend use of such Prospectus. The Company shall cause
      MergerCo to use its best efforts to ensure that the use of the Prospectus
      may be resumed as promptly as is practicable. The Company and MergerCo
      shall be entitled to exercise their right under this Section 3(i) to
      suspend the availability of a Registration Statement and Prospectus,
      subject to the payment of liquidated damages pursuant to Section 2(b), for
      a period not to exceed 60 days (which need not be consecutive days) in any
      12 month period.

            (j) Comply with all applicable rules and regulations of the
      Commission.

            (k) Use its best efforts to avoid the issuance of, or, if issued,
      obtain the withdrawal of (i) any order suspending the effectiveness of a
      Registration Statement, or (ii) any suspension of the qualification (or
      exemption from qualification) of any of the Registrable Securities for
      sale in any jurisdiction, at the earliest practicable moment.


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<PAGE>

            (l) MergerCo may require each Holder to furnish to MergerCo a
      certified statement as to (i) the number of shares of Common Stock
      beneficially owned by such Holder, (ii) if required by the Commission, the
      holder thereof or the person that has voting and dispositive control over
      such shares, (iii) any relationship between such Holder and MergerCo and
      (iv) such other information regarding such Holder as shall be required by
      the Commission or the National Association of Securities Dealers. If any
      such Holder fails to furnish such information within three Trading Days of
      MergerCo's request, MergerCo or the Company shall furnish written notice
      of such non-compliance to such Holder, the Placement Agent and the
      Placement Agent's counsel. If, for a period of two Trading Days after such
      notice is given, such Holder continues to fail to furnish such
      information, then (i) MergerCo shall no longer be obligated to include any
      of such Holder's Registrable Securities as part of the Registration
      Statement (provided, however, in the event such Holder provides such
      information to MergerCo prior to the time when MergerCo files a request
      for acceleration, the Company shall cause MergerCo to register such
      Holder's Registrable Securities as part of the Registration Statement) and
      (ii) the Company shall have no obligation to pay any liquidated damages to
      such Holder with respect to any Event. In the event that (i) the
      immediately preceding sentence applies, (ii) subsequent to the filing of
      the above-mentioned request for acceleration such Holder provides such
      information to MergerCo and (iii) thereafter MergerCo files another
      registration statement in which MergerCo may include such Holder's
      securities without significant cost to MergerCo and with the consent of
      any applicable underwriter, then MergerCo shall use its best efforts to
      include such Holder's Registrable Securities in such registration
      statement in accordance with customary arrangements applicable to
      piggyback registration rights.

            (m) Notwithstanding anything contained in this Agreement, the right
      of any Holder to request or demand inclusion in any registration hereunder
      shall terminate as to Shares of Registrable Securities held by such Holder
      that may be immediately sold under Rule 144(k).

      4. Registration Expenses. All fees and expenses incident to the
performance of or compliance with this Agreement by MergerCo shall be borne by
MergerCo whether or not any Registrable Securities are sold pursuant to the
Registration Statement. The fees and expenses referred to in the foregoing
sentence shall include, without limitation, (i) all registration and filing fees
(including, without limitation, fees and expenses (A) with respect to filings
required to be made with the Trading Market on which the Common Stock is then
listed for trading and (B) in compliance with applicable state securities or
Blue Sky laws), (ii) printing expenses (including, without limitation, expenses
of printing certificates for Registrable Securities and of printing prospectuses
if the printing of prospectuses is reasonably requested by the holders of a
majority of the Registrable Securities included in the Registration Statement),
(iii) messenger, telephone and delivery expenses, (iv) fees and disbursements of
counsel for MergerCo, (v) Securities Act liability insurance, if MergerCo so
desires such insurance, and (vi) fees and expenses of all other Persons retained
by MergerCo in connection with the consummation of the transactions contemplated
by this Agreement. In addition, MergerCo shall be responsible for all of its
internal expenses incurred in connection with the consummation of the
transactions contemplated by this Agreement (including, without limitation, all
salaries and expenses of its officers and employees performing legal or
accounting duties), the expense of any annual audit and the fees and expenses
incurred in connection with the listing of the Registrable Securities on any
securities exchange as required hereunder. In no event shall MergerCo be
responsible for any broker or similar commissions or, except to the extent
provided for in the Transaction Documents, any legal fees or other costs of the
Holders.

      5. Indemnification.


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            (a) Indemnification by the Company. MergerCo shall, notwithstanding
      any termination of this Agreement, indemnify and hold harmless each
      Holder, the officers, directors, agents and employees of each of them,
      each Person who controls any such Holder (within the meaning of Section 15
      of the Securities Act or Section 20 of the Exchange Act) and the officers,
      directors, agents and employees of each such controlling Person, to the
      fullest extent permitted by applicable law, from and against any and all
      losses, claims, damages, liabilities, costs (including, without
      limitation, reasonable attorneys' fees) and expenses (collectively,
      "Losses"), as incurred, arising out of or relating to any untrue or
      alleged untrue statement of a material fact contained in the Registration
      Statement, any Prospectus or any form of prospectus or in any amendment or
      supplement thereto or in any preliminary prospectus, or arising out of or
      relating to any omission or alleged omission of a material fact required
      to be stated therein or necessary to make the statements therein (in the
      case of any Prospectus or form of prospectus or supplement thereto, in
      light of the circumstances under which they were made) not misleading,
      except to the extent, but only to the extent, that (i) such untrue
      statements or omissions are based solely upon information regarding such
      Holder furnished in writing to the Company or MergerCo by such Holder
      expressly for use therein, or to the extent that such information relates
      to such Holder or such Holder's proposed method of distribution of
      Registrable Securities and was reviewed and expressly approved in writing
      by such Holder expressly for use in the Registration Statement, such
      Prospectus or such form of Prospectus or in any amendment or supplement
      thereto (it being understood that the Holder has approved Annex A hereto
      for this purpose) or (ii) in the case of an occurrence of an event of the
      type specified in Section 3(c)(ii)-(vi), the use by such Holder of an
      outdated or defective Prospectus after the Company has notified such
      Holder in writing that the Prospectus is outdated or defective and prior
      to the receipt by such Holder of the Advice contemplated in Section 6(d).
      The Company shall notify the Holders promptly of the institution, threat
      or assertion of any Proceeding of which the Company is aware in connection
      with the transactions contemplated by this Agreement.

            (b) Indemnification by Holders. Each Holder shall, severally and not
      jointly, indemnify and hold harmless MergerCo, its directors, officers,
      agents and employees, each Person who controls MergerCo (within the
      meaning of Section 15 of the Securities Act and Section 20 of the Exchange
      Act), and the directors, officers, agents or employees of such controlling
      Persons, to the fullest extent permitted by applicable law, from and
      against all Losses, as incurred, to the extent arising out of or based
      solely upon: (x) such Holder's failure to comply with the prospectus
      delivery requirements of the Securities Act or (y) any untrue or alleged
      untrue statement of a material fact contained in any Registration
      Statement, any Prospectus, or any form of prospectus, or in any amendment
      or supplement thereto or in any preliminary prospectus, or arising out of
      or relating to any omission or alleged omission of a material fact
      required to be stated therein or necessary to make the statements therein
      not misleading (i) to the extent, but only to the extent, that such untrue
      statement or omission is contained in any information so furnished in
      writing by such Holder to MergerCo specifically for inclusion in the
      Registration Statement or such Prospectus or (ii) to the extent that (1)
      such untrue statements or omissions are based solely upon information
      regarding such Holder furnished in writing to MergerCo by such Holder
      expressly for use therein, or to the extent that such information relates
      to such Holder or such Holder's proposed method of distribution of
      Registrable Securities and was reviewed and expressly approved in writing
      by such Holder expressly for use in the Registration Statement (it being
      understood that the Holder has approved Annex A hereto for this purpose),
      such Prospectus or such form of Prospectus or in any amendment or
      supplement thereto or (2) in the case of an occurrence of an event of the
      type specified in Section 3(c)(ii)-(vi), the use by such Holder of an
      outdated or defective Prospectus after the Company has notified such
      Holder in writing that the Prospectus is outdated or defective and prior
      to the receipt by such Holder of the Advice contemplated in Section 6(d).
      In no event shall the liability of any selling Holder hereunder be greater
      in amount than the dollar amount of the net proceeds received by such
      Holder upon the sale of the Registrable Securities giving rise to such
      indemnification obligation.


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<PAGE>

            (c) Conduct of Indemnification Proceedings. (i) If any Proceeding
      shall be brought or asserted against any Person entitled to indemnity
      hereunder (an "Indemnified Party"), such Indemnified Party shall promptly
      notify the Person from whom indemnity is sought (the "Indemnifying Party")
      in writing, and the Indemnifying Party shall have the right to assume the
      defense thereof, including the employment of counsel reasonably
      satisfactory to the Indemnified Party and the payment of all fees and
      expenses incurred in connection with defense thereof; provided, that the
      failure of any Indemnified Party to give such notice shall not relieve the
      Indemnifying Party of its obligations or liabilities pursuant to this
      Agreement, except (and only) to the extent that it shall be finally
      determined by a court of competent jurisdiction (which determination is
      not subject to appeal or further review) that such failure shall have
      prejudiced the Indemnifying Party.

            (ii) An Indemnified Party shall have the right to employ separate
      counsel in any such Proceeding and to participate in the defense thereof,
      but the fees and expenses of such counsel shall be at the expense of such
      Indemnified Party or Parties unless: (1) the Indemnifying Party has agreed
      in writing to pay such fees and expenses; (2) the Indemnifying Party shall
      have failed promptly to assume the defense of such Proceeding and to
      employ counsel reasonably satisfactory to such Indemnified Party in any
      such Proceeding; or (3) the named parties to any such Proceeding
      (including any impleaded parties) include both such Indemnified Party and
      the Indemnifying Party, and such Indemnified Party shall reasonably
      believe that a material conflict of interest is likely to exist if the
      same counsel were to represent such Indemnified Party and the Indemnifying
      Party (in which case, if such Indemnified Party notifies the Indemnifying
      Party in writing that it elects to employ separate counsel at the expense
      of the Indemnifying Party, the Indemnifying Party shall not have the right
      to assume the defense thereof and the reasonable fees and expenses of one
      separate counsel shall be at the expense of the Indemnifying Party). The
      Indemnifying Party shall not be liable for any settlement of any such
      Proceeding effected without its written consent, which consent shall not
      be unreasonably withheld. No Indemnifying Party shall, without the prior
      written consent of the Indemnified Party, effect any settlement of any
      pending Proceeding in respect of which any Indemnified Party is a party,
      unless such settlement includes an unconditional release of such
      Indemnified Party from all liability on claims that are the subject matter
      of such Proceeding.

            (iii) Subject to the terms of this Agreement, all reasonable fees
      and expenses of the Indemnified Party (including reasonable fees and
      expenses to the extent incurred in connection with investigating or
      preparing to defend such Proceeding in a manner not inconsistent with this
      Section) shall be paid to the Indemnified Party, as incurred, within ten
      Trading Days of written notice thereof to the Indemnifying Party;
      provided, that the Indemnified Party shall promptly reimburse the
      Indemnifying Party for that portion of such fees and expenses applicable
      to such actions for which such Indemnified Party is not entitled to
      indemnification hereunder, determined based upon the relative faults of
      the parties.

            (d) Contribution. (i) If a claim for indemnification under Section
      5(a) or 5(b) is unavailable to an Indemnified Party (by reason of public
      policy or otherwise), then each Indemnifying Party, in lieu of
      indemnifying such Indemnified Party, shall contribute to the amount paid
      or payable by such Indemnified Party as a result of such Losses, in such
      proportion as is appropriate to reflect the relative fault of the
      Indemnifying Party and Indemnified Party in connection with the actions,
      statements or omissions that resulted in such Losses as well as any other
      relevant equitable considerations. The relative fault of such Indemnifying
      Party and Indemnified Party shall be determined by reference to, among
      other things, whether any action in question, including any untrue or
      alleged untrue statement of a material fact or omission or alleged
      omission of a material fact, has been taken or made by, or relates to
      information supplied by, such Indemnifying Party or Indemnified Party, and
      the parties' relative intent, knowledge, access to information and
      opportunity to correct or prevent such action, statement or omission. The
      amount paid or payable by a party as a result of any Losses shall be
      deemed to include, subject to the limitations set forth in this Agreement,
      any reasonable attorneys' or other reasonable fees or expenses incurred by
      such party in connection with any Proceeding to the extent such party
      would have been indemnified for such fees or expenses if the
      indemnification provided for in this section was available to such party
      in accordance with its terms.


                                       9
<PAGE>

            (ii) The parties hereto agree that it would not be just and
      equitable if contribution pursuant to this Section 5(d) were determined by
      pro rata allocation or by any other method of allocation that does not
      take into account the equitable considerations referred to in the
      immediately preceding paragraph. Notwithstanding the provisions of this
      Section 5(d), no Holder shall be required to contribute, in the aggregate,
      any amount in excess of the amount by which the proceeds actually received
      by such Holder from the sale of the Registrable Securities subject to the
      Proceeding exceeds the amount of any damages that such Holder has
      otherwise been required to pay by reason of such untrue or alleged untrue
      statement or omission or alleged omission, except in the case of fraud by
      such Holder.

            (iii) The indemnity and contribution agreements contained in this
      Section are in addition to any liability that the Indemnifying Parties may
      have to the Indemnified Parties.

      6. Miscellaneous

            (a) Remedies. In the event of a breach by the Company or MergerCo,
      on one hand, or by a Holder, on the other hand, of any of their respective
      obligations under this Agreement, each Holder or the Company and MergerCo,
      as the case may be, in addition to being entitled to exercise all rights
      granted by law and under this Agreement, including recovery of damages,
      will be entitled to specific performance of its rights under this
      Agreement. The Company, MergerCo and each Holder each agrees that monetary
      damages would not provide adequate compensation for any losses incurred by
      reason of a breach by it of any of the provisions of this Agreement and
      hereby further agrees that, in the event of any action for specific
      performance in respect of such breach, it shall waive the defense that a
      remedy at law would be adequate.

            (b) No Piggyback on Registrations. Except as set forth on Schedule
      6(b) attached hereto, neither the Company nor any of its security holders
      (other than the Holders in such capacity pursuant hereto) may include
      securities of the Company or MergerCo in a Registration Statement other
      than the Registrable Securities and no Person has any right to cause the
      Company to effect the registration under the Securities Act of any
      securities of the Company. MergerCo shall not file any other registration
      statement (other than on Form S-8) until after the Effective Date.

            (c) Compliance. Each Holder covenants and agrees that it will comply
      with the Prospectus delivery requirements of the Securities Act as
      applicable to it in connection with offers and sales of Registrable
      Securities pursuant to the Registration Statement.

            (d) Discontinued Disposition. Each Holder agrees by its acquisition
      of such Registrable Securities that, upon receipt of a notice from the
      Company or MergerCo of the occurrence of any event of the kind described
      in Section 3(c), such Holder will forthwith discontinue disposition of
      such Registrable Securities under the Registration Statement until such
      Holder's receipt of the copies of the supplemented Prospectus and/or
      amended Registration Statement or until it is advised in writing (the
      "Advice") by the Company or MergerCo that the use of the applicable
      Prospectus may be resumed, and, in either case, has received copies of any
      additional or supplemental filings that are incorporated or deemed to be
      incorporated by reference in such Prospectus or Registration Statement.
      MergerCo will use its best efforts to ensure that the use of the
      Prospectus may be resumed as promptly as is practicable. MergerCo agrees
      and acknowledges that any periods during which the Holder is required to
      discontinue the disposition of the Registrable Securities hereunder shall
      be subject to the provisions of Section 2(b).


                                       10
<PAGE>

            (e) Piggy-Back Registrations. If at any time during the
      Effectiveness Period there is not an effective Registration Statement
      covering all of the Registrable Securities and MergerCo shall determine to
      prepare and file with the Commission a registration statement relating to
      an offering for its own account or the account of others under the
      Securities Act of any of its equity securities, other than on Form S-4 or
      Form S-8 (each as promulgated under the Securities Act) or their then
      equivalents relating to equity securities to be issued solely in
      connection with any acquisition of any entity or business or equity
      securities issuable in connection with the stock option or other employee
      benefit plans, then MergerCo shall send to each Holder a written notice of
      such determination and, if within fifteen days after the date of such
      notice, any such Holder shall so request in writing, MergerCo shall
      include in such registration statement all or any part of such Registrable
      Securities such Holder requests to be registered, subject to customary
      underwriter cutbacks applicable to all holders of registration rights.

            (f) Amendments and Waivers. The provisions of this Agreement,
      including the provisions of this sentence, may not be amended, modified or
      supplemented, and waivers or consents to departures from the provisions
      hereof may not be given, unless the same shall be in writing and signed by
      the Company and Holders of not less than two-thirds (2/3) of the then
      outstanding Registrable Securities.

            (g) Notices. Any and all notices or other communications or
      deliveries required or permitted to be provided hereunder shall be made in
      accordance with the provisions of the Purchase Agreement.

            (h) Successors and Assigns. This Agreement shall inure to the
      benefit of and be binding upon the successors and permitted assigns of
      each of the parties and shall inure to the benefit of each Holder. Each
      Holder may assign their respective rights hereunder only in the manner and
      to the Persons as permitted under the Purchase Agreement.

            (i) Execution and Counterparts. This Agreement may be executed in
      any number of counterparts, each of which when so executed shall be deemed
      to be an original and, all of which taken together shall constitute one
      and the same Agreement. In the event that any signature is delivered by
      facsimile transmission, such signature shall create a valid binding
      obligation of the party executing (or on whose behalf such signature is
      executed) the same with the same force and effect as if such facsimile
      signature were the original thereof.

            (j) Governing Law. All questions concerning the construction,
      validity, enforcement and interpretation of this Agreement shall be
      governed by and construed in accordance with the internal laws of the
      State of New York, without regard to the principles of conflicts of law
      thereof.

            (k) Cumulative Remedies. The remedies provided herein are cumulative
      and not exclusive of any remedies provided by law.


                                       11
<PAGE>

            (l) Severability. If any term, provision, covenant or restriction of
      this Agreement is held by a court of competent jurisdiction to be invalid,
      illegal, void or unenforceable, the remainder of the terms, provisions,
      covenants and restrictions set forth herein shall remain in full force and
      effect and shall in no way be affected, impaired or invalidated, and the
      parties hereto shall use their commercially reasonable efforts to find and
      employ an alternative means to achieve the same or substantially the same
      result as that contemplated by such term, provision, covenant or
      restriction. It is hereby stipulated and declared to be the intention of
      the parties that they would have executed the remaining terms, provisions,
      covenants and restrictions without including any of such that may be
      hereafter declared invalid, illegal, void or unenforceable.

            (m) Headings. The headings in this Agreement are for convenience of
      reference only and shall not limit or otherwise affect the meaning hereof.

            (n) Independent Nature of Purchasers' Obligations and Rights. The
      obligations of each Holder hereunder are several and not joint with the
      obligations of any other Holder hereunder, and no Holder shall be
      responsible in any way for the performance of the obligations of any other
      Holder hereunder. Nothing contained herein or in any other agreement or
      document delivered at any closing, and no action taken by any Holder
      pursuant hereto or thereto, shall be deemed to constitute the Holders as a
      partnership, an association, a joint venture or any other kind of entity,
      or create a presumption that the Holders are in any way acting in concert
      with respect to such obligations or the transactions contemplated by this
      Agreement. Each Holder shall be entitled to protect and enforce its
      rights, including without limitation the rights arising out of this
      Agreement, and it shall not be necessary for any other Holder to be joined
      as an additional party in any proceeding for such purpose.

                [Remainder of this page intentionally left blank]



                                       12
<PAGE>

            IN WITNESS WHEREOF, the parties have executed this Registration
Rights Agreement as of the date first written above.

                                        OSTEOLOGIX, INC.

                                        By:
                                            ------------------------------------
                                            Name:  Charles J. Casamento
                                            Title: Chief Executive Officer

                                        CASTLE & MORGAN HOLDINGS, INC.

                                        By:
                                            ------------------------------------
                                            Name:  Geoffrey Alison
                                            Title: Chief Executive Officer
<PAGE>

           PURCHASER'S SIGNATURE PAGE TO REGISTRATION RIGHTS AGREEMENT

Name of Investing Entity: __________________________
Signature of Authorized Signatory of Investing Entity: _________________________
Name of Authorized Signatory: _________________________
Title of Authorized Signatory: __________________________
<PAGE>

                                     ANNEX A

                              Plan of Distribution

The Selling Stockholders (the "Selling Stockholders") of the common stock
("Common Stock") of Osteologix, Inc. (the "Company") and any of their pledgees,
assignees and successors-in-interest may, from time to time, sell any or all of
their shares of Common Stock on any stock exchange, market or trading facility
on which the shares are traded or in private transactions. These sales may be at
fixed or negotiated prices. The Selling Stockholders may use any one or more of
the following methods when selling shares:

      o     ordinary brokerage transactions and transactions in which the
            broker-dealer solicits purchasers;

      o     block trades in which the broker-dealer will attempt to sell the
            shares as agent but may position and resell a portion of the block
            as principal to facilitate the transaction;

      o     purchases by a broker-dealer as principal and resale by the
            broker-dealer for its account;

      o     an exchange distribution in accordance with the rules of the
            applicable exchange;

      o     privately negotiated transactions;

      o     settlement of short sales entered into after the date of this
            prospectus;

      o     broker-dealers may agree with the Selling Stockholders to sell a
            specified number of such shares at a stipulated price per share;

      o     a combination of any such methods of sale;

      o     through the writing or settlement of options or other hedging
            transactions, whether through an options exchange or otherwise; or

      o     any other method permitted pursuant to applicable law.

      The Selling Stockholders may also sell shares under Rule 144 under the
Securities Act of 1933, as amended (the "Securities Act"), if available, rather
than under this prospectus.

      Broker-dealers engaged by the Selling Stockholders may arrange for other
brokers-dealers to participate in sales. Broker-dealers may receive commissions
or discounts from the Selling Stockholders (or, if any broker-dealer acts as
agent for the purchaser of shares, from the purchaser) in amounts to be
negotiated. Each Selling Stockholder does not expect these commissions and
discounts relating to its sales of shares to exceed what is customary in the
types of transactions involved.

      In connection with the sale of our common stock or interests therein, the
Selling Stockholders may enter into hedging transactions with broker-dealers or
other financial institutions, which may in turn engage in short sales of the
common stock in the course of hedging the positions they assume. The Selling
Stockholders may also sell shares of our common stock short and deliver these
securities to close out their short positions, or loan or pledge the common
stock to broker-dealers that in turn may sell these securities. The Selling
Stockholders may also enter into option or other transactions with
broker-dealers or other financial institutions or the creation of one or more
derivative securities which require the delivery to such broker-dealer or other
financial institution of shares offered by this prospectus, which shares such
broker-dealer or other financial institution may resell pursuant to this
prospectus (as supplemented or amended to reflect such transaction).
<PAGE>

      The Selling Stockholders and any broker-dealers or agents that are
involved in selling the shares may be deemed to be "underwriters" within the
meaning of the Securities Act in connection with such sales. In such event, any
commissions received by such broker-dealers or agents and any profit on the
resale of the shares purchased by them may be deemed to be underwriting
commissions or discounts under the Securities Act. Each Selling Stockholder has
informed the Company that it does not have any agreement or understanding,
directly or indirectly, with any person to distribute the Common Stock.

      The Company is required to pay certain fees and expenses incurred by the
Company incident to the registration of the shares. The Company has agreed to
indemnify the Selling Stockholders against certain losses, claims, damages and
liabilities, including liabilities under the Securities Act.

      Because Selling Stockholders may be deemed to be "underwriters" within the
meaning of the Securities Act, they will be subject to the prospectus delivery
requirements of the Securities Act. In addition, any securities covered by this
prospectus which qualify for sale pursuant to Rule 144 under the Securities Act
may be sold under Rule 144 rather than under this prospectus. Each Selling
Stockholder has advised us that they have not entered into any agreements,
understandings or arrangements with any underwriter or broker-dealer regarding
the sale of the resale shares. There is no underwriter or coordinating broker
acting in connection with the proposed sale of the resale shares by the Selling
Stockholders.

      We agreed to keep this prospectus effective until the earlier of (i) the
date on which the shares may be resold by the Selling Stockholders without
registration and without regard to any volume limitations by reason of Rule
144(e) under the Securities Act or any other rule of similar effect or (ii) all
of the shares have been sold pursuant to the prospectus or Rule 144 under the
Securities Act or any other rule of similar effect. The resale shares will be
sold only through registered or licensed brokers or dealers if required under
applicable state securities laws. In addition, in certain states, the resale
shares may not be sold unless they have been registered or qualified for sale in
the applicable state or an exemption from the registration or qualification
requirement is available and is complied with.

      Under applicable rules and regulations under the Securities Exchange Act
of 1934, as amended, any person engaged in the distribution of the resale shares
may not simultaneously engage in market making activities with respect to our
common stock for a period of two business days prior to the commencement of the
distribution. In addition, the Selling Stockholders will be subject to
applicable provisions of the Exchange Act and the rules and regulations
thereunder, including Regulation M, which may limit the timing of purchases and
sales of shares of our common stock by the Selling Stockholders or any other
person. We will make copies of this prospectus available to the Selling
Stockholders and have informed them of the need to deliver a copy of this
prospectus to each purchaser at or prior to the time of the sale.
<PAGE>

                                  Schedule 6(b)
                             Piggyback Registrations

         Registration Rights Agreement with holders of shares of Common Stock of
MergerCo prior to the Merger relating to the registration of an aggregate of
2,715,634 shares.