A group of muscles located within or situated deeper in a structure, in contrast to extrinsic muscles located rather superficially
Based on the above definition, the intrinsic muscles refer to the muscles closest to the axial and appendicular skeleton. For example, the intrinsic muscles of the hand are those lying deeper in the hand, such as the interossei and lumbrical muscles.
In another view, the intrinsic muscles of the tongue pertain to the muscles within the tongue with their insertions and origins within the tongue as well. Intrinsic muscles of the tongue include the superior longitudinal muscle, the inferior longitudinal muscle, the transverse muscle, and the veticalis muscle.