37 C.F.R. § 41.39 : Patents, Trademarks, and Copyrights — UNITED STATES PATENT AND TRADEMARK OFFICE, DEPARTMENT OF COMMERCE — GENERAL PATENTS — PRACTICE BEFORE THE PATENT TRIAL AND APPEAL BOARD — APPEALS — Examiner's answer

(a) Content of examiner's answer. The primary examiner may, within such time as may be directed by the Director, furnish a written answer to the appeal brief.
(1) An examiner's answer is deemed to incorporate all of the grounds of rejection set forth in the Office action from which the appeal is taken (as modified by any advisory action and pre-appeal brief conference decision), unless the examiner's answer expressly indicates that a ground of rejection has been withdrawn.
(2) An examiner's answer may include a new ground of rejection. For purposes of the examiner's answer, any rejection that relies upon any Evidence not relied upon in the Office action from which the appeal is taken (as modified by any advisory action) shall be designated by the primary examiner as a new ground of rejection. The examiner must obtain the approval of the Director to furnish an answer that includes a new ground of rejection.
(b) Appellant's response to new ground of rejection. If an examiner's answer contains a rejection designated as a new ground of rejection, appellant must within two months from the date of the examiner's answer exercise one of the following two options to avoid sua sponte dismissal of the appeal as to the claims subject to the new ground of rejection:
(1) Reopen prosecution . Request that prosecution be reopened before the primary examiner by filing a reply under §1.111 of this title with or without amendment or submission of affidavits (§§1.130, 1.131 or 1.132 of this of this title) or other Evidence. Any amendment or submission of affidavits or other Evidence must be relevant to the new ground of rejection. A request that complies with this paragraph will be entered and the application or the patent under ex parte reexamination will be reconsidered by the examiner under the provisions of §1.112 of this title. Any request that prosecution be reopened under this paragraph will be treated as a request to withdraw the appeal.
(2) Maintain appeal . Request that the appeal be maintained by filing a reply brief as set forth in §41.41. Such a reply brief must address as set forth in §41.37(c)(1)(iv) each new ground of rejection and should follow the other requirements of a brief as set forth in §41.37(c). A reply brief may not be accompanied by any amendment, affidavit (§§1.130, 1.131 or 1.132 of this of this title) or other Evidence. If a reply brief filed pursuant to this section is accompanied by any amendment, affidavit or other Evidence, it shall be treated as a request that prosecution be reopened before the primary examiner under paragraph (b)(1) of this section.
(c) Extensions of time. Extensions of time under §1.136(a) of this title for patent applications are not applicable to the time period set forth in this section. See §1.136(b) of this title for extensions of time to reply for patent applications and §1.550(c) of this title for extensions of time to reply for ex parte reexamination proceedings.

37 C.F.R. §41.39

69 FR 50003, 8/12/2004, as amended at 76 FR 72298, 11/22/2011