A head portion of a surgical instrument, the head portion comprising: a shell assembly including a non-planar tissue-contacting surface and an anvil assembly having a non-planar tissue-contacting surface, the non-planar tissue-contacting surface of the anvil assembly divided into at most two curvilinear segments, each curvilinear segment including at most one concave portion and at most one convex portion, wherein the tissue-contacting surface of the anvil assembly is configured to align with the tissue-contacting surface of the shell assembly when the anvil assembly and the shell assembly are in an approximated position.
