code: def _get_subject_sphere_tris(subject, subjects_dir):
      spheres = [
          subjects_dir / subject / "surf" / (xh + ".sphere.reg")
          for xh in ["lh", "rh"]
      ]
      tris = [read_surface(s)[1] for s in spheres]
      return tris
  
imports: import copy
  import os.path
  import warnings
  import numpy
  from scipy import sparse
  from .fixes import _get_img_fdata
  from .morph_map import read_morph_map
  from .parallel import parallel_func
  from .source_estimate import _BaseSourceEstimate, _BaseSurfaceSourceEstimate, _BaseVolSourceEstimate, _get_ico_tris
  from .source_space._source_space import SourceSpaces, _ensure_src, _grid_interp
  from .surface import _compute_nearest, mesh_edges, read_surface
  from .utils import BunchConst, ProgressBar, _check_fname, _check_option, _custom_lru_cache, _ensure_int, _import_h5io_funcs, _import_nibabel, _validate_type, check_version, fill_doc, get_subjects_dir, logger, use_log_level, verbose, warn
  from .utils import warn
label_desc: Use image node_id 21 for calling a global function with example usage: _get_subject_sphere_tris(subject, subjects_dir) and returns: tris